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Posted to dev@flink.apache.org by Becket Qin <be...@gmail.com> on 2022/01/04 05:40:35 UTC
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Hi David,
Thanks for sharing your thoughts. Some quick reply to your comments:
We're still talking about the "web server based"
> pattern_processor_discoverer, but what about other use cases? One of my big
> concerns is that user's can not really reuse any part of the Flink
> ecosystem to implement the discovery logic. For example if they want to
> read patterns from Kafka topic, they need to roll their own discoverer
> based on the vanilla Kafka client. If we're talking about extensibility,
> should we also make sure that the existing primitives can be reused?
KafkaSource is actually more complicated than vanilla KafkaConsumer from
the perspective of consuming Kafka messages. The KafkaSource just helps
make it easier for Flink jobs to process these messages. In fact,
KafkaConsumer is more powerful than KafkaSource in terms of talking to
Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator] and
[KafkaSource + side-input], not [KafkaConsumer + side-input].
This can be done for the side-input as well by filtering invalid patterns
> before the broadcast. You can also send the invalid patterns to any side
> output you want. I have a feeling that we're way too attached to the REST
> server use case in this discussion. I agree that for that case, this
> solution is the most straightforward one.
Depending on whether the invalidity is discovered in pattern definition
time or data processing time. e.g. A valid pattern with invalid data which
fails to process can only be detected in data processing time. So the
pattern won't be filtered out before the broadcast.
I agree that 2-way communication in the "data-flow like" API is tricky,
> because it requires cycles / iterations, which are still not really solved
> (for a good reason, it's really tough nut to crack). This makes me think
> that the OC may be bit of a "incomplete" workaround for not having fully
> working support for iterations.
For example I'm not really confident that the checkpointing of the OC works
> correctly right now, because it doesn't seem to require checkpoint barrier
> alignment as the regular stream inputs. We also don't have a proper support
> for watermarking (this is again tricky, because of the cycle).
If we decide to go down this road, should we first address some of these
> limitations?
I agree. OC is proven to be useful and we should think about how to enhance
it instead of not using it.
If I understand that correctly, this means only the LATEST state of the
> patterns (in other words - patterns that are currently in use). Is this
> really sufficient for historical re-processing? Can someone for example
> want re-process the data in more of a "temporal join" fashion? Also AFAIK
> historical processing in combination with "coordinator checkpoints" is not
> really something that we currently support of the box, are there any plans
> on tackling this (my other concern is that this should not go against the
> "unified batch & stream processing" efforts)?
I think in this case, the state would contain the entire pattern update
history. Not the final state, but the change log. In fact, it is not
possible to guarantee the correct result unless you have the entire change
log. Even with side-input, there still could be late arrivals in the
pattern update stream, and the only way to correct it is to either have all
the data reprocessed (with all the pattern change log loaded upfront) or
having retraction support.
I can imagine that if this should be a concern, we could move the execution
> of the OC to the task managers. This also makes me thing, that we shouldn't
> make any strong assumptions that the OC will always run in the JobManager
> (this is especially relevant for the embedded web-server use case).
This is a very good point. I think we should do this. The reason OC is in
JM is based on the assumption that control plane usually have little
traffic. But if that is not the case, we should move the OC out of JM,
maybe to TM.
I think the key topic we are discussing is what the Flink control plane
should look like, and CEP is just an example use case. There are basically
two options:
1. Using the side-input / broadcast stream
2. Using the OperatorCoordinator.
Although we are having this discussion under the context of supporting CEP
dynamic pattern update, it would be really helpful to reach agreement on
the design principle in general of how Flink should handle similar external
control demands, a.k.a how to provide a decent control plane in Flink to
the users.
Here is my take on these two options, based on the requirements of a
control plane.
*Communication Requirements*
Flink has two kinds of control planes - in-band and out-of-band.
In-band control plane is like watermark and checkpoint marker. It requires
the entire DAG to be in a consistent state, so the control messages flow
with the data in one direction. This is a one-way control flow.
Examples of out-of-band control plane is OC and JM/TM communication. They
do not require a global consistency or awareness across the entire DAG.
Before OC, neither of these two kinds of control plain was exposed to the
users. OC allows the users to leverage the out-of-band control plane so
they can coordinate across subtasks. This is a more widely used control
flow from user defined operator perspective which requires 2-way
communication.
- side-input stream is one-way communication. Moreover, I don't think
iteration is the right way to address this. Unlike the abstraction of data
processing which is a DAG, the control plane may require communication
between arbitrary two operators in different orders. Using iterations may
end up with an explosion of feedback edges that are not only complicated to
express, but also hard to debug and maintain.
- OC provides a decent 2-way communication mechanism.
*Cost for low traffic use case*
An important difference between data channel and control channel is traffic
pattern. Unlike data plane, the control plane is usually idle for the vast
majority of the time with occasional control messages.
- One argument to use the side-input / broadcast stream was that users
can reuse the existing connectors. However, most Flink sources are designed
to handle large throughput of traffic that maintains all the threads,
network connections, etc. Not to say the external resources such as Kafka
topics to store the commands.
- OC can have a much lower constant cost.
*Easy to use*
Personally speaking, I think the most simple and user-friendly interface is
a REST API that accepts control commands.
- One proposal at this point is to have a separate web server
independent of the Flink job. In that case, should users implement that web
server? In order to pass the command to the Flink job, does that mean users
should implement a Flink source that can read the commands from the web
server? Or the web server would send the command to something like Kafka
and let the Flink side-input read from there. There seems to be a lot for
the users to do. And it seems an unnecessarily complicated system to build
to send occasional control messages to a Flink job.
- OC can simply be reached via the JM REST API.
- e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
<http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx> would simply
send the Content to the OC of OP_NAME.
*Work well with checkpoints*
- side-input streams works well with checkpoint, thanks to its
compatibility to the DAG abstraction.
- The OperatorCoordinator requires more careful design to work well with
checkpoints. The complexity mostly comes from the 2-way communication. At
this point the OperatorCoordinator message delivery semantic may not be as
robust as side-input streams. However, I think this is mainly due to
potential bugs in implementation instead of fundamental design problems.
Basically the checkpoint semantic should be:
- The JM will first checkpoint all the OperatorCoordinator, more
specifically for each OperatorCoordinator,
- 1) JM blocks the input queue to stop receiving new events from
the subtasks.
- 2) let all the operator coordinator finish processing all the
pending events in the OC input queue.
- 3) flush the OC output queue until all the events sent are
acknowledged.
- 3) unblock the input queue, but block the output queue until all
the subtasks of the OC finish checkpoints.
- The JM starts a normal checkpoint starting from the Source.
- If an operator has a coordinator, and it has sent some events to
the OC but has not been acknowledged. These events need to be
put into the
subtasks' checkpoint.
- After all the subtasks of an operator finishes checkpoint, the
output queue of the corresponding OC can be unblocked.
It looks that the above protocol would let OC have a clear checkpoint
semantic. And this complexity seems must for 2-way communication. I think
we are able to hide the above protocol from users by having an abstract OC
implementation.
*Reprocess command history and repeatable processing results*
This seems not something generally required for a control plane. But if the
control plane changes the data processing behavior, there might be some use
case. Just like the CEP pattern update. In order to do this, users will
need to provide a full command history to the operators. That consists of
two steps:
1. get the full command history. (Flink Source V.S. Custom way to
retrieve command history.)
2. send them to the operators. (Side-input V.S. OC/Operator
communication)l
I actually don't feel much difference between these two options. I am not
sure if a Flink source is necessarily simpler than the user implemented
logic. For example, if all the changes are just written in a database
table. From the user's perspective, I feel fine with querying the DB by
myself using something like JDBC (or use KafkaConsumer to read the pattern
history from a Kafka topic) and send all the pattern change history to the
operators before they start to process the actual events.
*Stability impact to the Flink Job*
I agree this is a valid concern. There is only one JM and currently OC runs
there, which may potentially cause JM crash and result in job failure.
Running in TM may have a less impact. So I think it makes sense to run OC
in TM. However, this is more of how we can implement OC to make it more
robust. It does not forfeit the other semantic and user experience benefits
mentioned above.
To sum up:
1. Regardless of whether CEP chooses OC or side-input stream, a decent
2-way communication control plane seems really helpful and has been proven
by quite a few existing use cases. To me the question is how to make it
more robust, not whether we should use it or not.
2. As for CEP, if we assume OC will be robust enough, personally I feel OC
is a better fit than side-input mainly because of the simplicity and
extensibility.
Thanks,
Jiangjie (Becket) Qin
On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org> wrote:
> Hi all,
>
> sorry for the late reply, vacation season ;) I'm still not 100% sold on
> choosing the OC for this use-case, but on the other hand I don't have
> strong arguments against it. Few more questions / thoughts:
>
> We're still talking about the "web server based"
> pattern_processor_discoverer, but what about other use cases? One of my big
> concerns is that user's can not really reuse any part of the Flink
> ecosystem to implement the discovery logic. For example if they want to
> read patterns from Kafka topic, they need to roll their own discoverer
> based on the vanilla Kafka client. If we're talking about extensibility,
> should we also make sure that the existing primitives can be reused?
>
> For instance, the example I gave in my previous email seems not easily
> > achievable with side-input / broadcast streams: a single invalid pattern
> > detected on a TM can be disabled elegantly globally without crashing the
> > entire Flink job.
>
>
> This can be done for the side-input as well by filtering invalid patterns
> before the broadcast. You can also send the invalid patterns to any side
> output you want. I have a feeling that we're way too attached to the REST
> server use case in this discussion. I agree that for that case, this
> solution is the most straightforward one.
>
> OC is a 2-way communication mechanism, i.e. a subtask can also send
> > OperatorEvent to the coordinator to report its owns status, so that the
> > coordinator can act accordingly.
> >
>
> I agree that 2-way communication in the "data-flow like" API is tricky,
> because it requires cycles / iterations, which are still not really solved
> (for a good reason, it's really tough nut to crack). This makes me think
> that the OC may be bit of a "incomplete" workaround for not having fully
> working support for iterations.
>
> For example I'm not really confident that the checkpointing of the OC works
> correctly right now, because it doesn't seem to require checkpoint barrier
> alignment as the regular stream inputs. We also don't have a proper support
> for watermarking (this is again tricky, because of the cycle).
>
> If we decide to go down this road, should we first address some of these
> limitations?
>
> OperatorCoordinator will checkpoint the full amount of PatternProcessor
> > data. For the reprocessing of historical data, you can read the
> > PatternProcessor snapshots saved by this checkpoint from a certain
> > historical checkpoint, and then recreate the historical data through
> these
> > PatternProcessor snapshots.
> >
>
> If I understand that correctly, this means only the LATEST state of the
> patterns (in other words - patterns that are currently in use). Is this
> really sufficient for historical re-processing? Can someone for example
> want re-process the data in more of a "temporal join" fashion? Also AFAIK
> historical processing in combination with "coordinator checkpoints" is not
> really something that we currently support of the box, are there any plans
> on tackling this (my other concern is that this should not go against the
> "unified batch & stream processing" efforts)?
>
> I do agree that having the user defined control logic defined in the JM
> > increases the chance of instability.
> >
>
> I can imagine that if this should be a concern, we could move the execution
> of the OC to the task managers. This also makes me thing, that we shouldn't
> make any strong assumptions that the OC will always run in the JobManager
> (this is especially relevant for the embedded web-server use case).
>
> If an agreement is reached on OperatorCoodinator, I will start the voting
> > thread.
> >
>
> As for the vote, I'd would be great if we can wait until the next week as
> many people took vacation until end of the year.
>
> Overall, I really like the feature, this will be a great addition to Flink.
>
> Best,
> D.
>
>
>
> On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <ma...@ververica.com>
> wrote:
>
> > Hi all,
> >
> > I can understand the need for a control plane mechanism. I'm not the
> > technical go-to person for questions on the OperatorCoordinator, but I
> > would expect that we could offer those interfaces from Flink but
> shouldn't
> > recommend running user-code in the JobManager itself. I think the user
> code
> > (like a webserver) should run outside of Flink (like via a sidecar) and
> use
> > only the provided interfaces to communicate.
> >
> > I would like to get @David Morávek <dm...@apache.org> opinion on the
> > technical part.
> >
> > Best regards,
> >
> > Martijn
> >
> > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <ni...@apache.org>
> > wrote:
> >
> >> Hi Konstantin, Becket, Martijn,
> >>
> >> Thanks for sharing your feedback. What other concerns do you have about
> >> OperatorCoodinator? If an agreement is reached on OperatorCoodinator, I
> >> will start the voting thread.
> >>
> >> Best,
> >> Nicholas Jiang
> >>
> >> On 2021/12/22 03:19:58 Becket Qin wrote:
> >> > Hi Konstantin,
> >> >
> >> > Thanks for sharing your thoughts. Please see the reply inline below.
> >> >
> >> > Thanks,
> >> >
> >> > Jiangjie (Becket) Qin
> >> >
> >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <kn...@apache.org>
> >> wrote:
> >> >
> >> > > Hi Becket, Hi Nicholas,
> >> > >
> >> > > Thanks for joining the discussion.
> >> > >
> >> > > 1 ) Personally, I would argue that we should only run user code in
> the
> >> > > Jobmanager/Jobmaster if we can not avoid it. It seems wrong to me to
> >> > > encourage users to e.g. run a webserver on the Jobmanager, or
> >> continuously
> >> > > read patterns from a Kafka Topic on the Jobmanager, but both of
> these
> >> I see
> >> > > happening with the current design. We've had lots of issues with
> >> > > classloading leaks and other stability issues on the Jobmanager and
> >> making
> >> > > this more complicated, if there is another way, seems unnecessary.
> >> >
> >> >
> >> > I think the key question here is what primitive does Flink provide to
> >> > facilitate the user implementation of their own control logic /
> control
> >> > plane? It looks that previously, Flink assumes that all the user logic
> >> is
> >> > just data processing logic without any control / coordination
> >> requirements.
> >> > However, it turns out that a decent control plane abstraction is
> >> required
> >> > in association with the data processing logic in many cases, including
> >> > Source / Sink and other user defined operators in general. The fact
> >> that we
> >> > ended up with adding the SplitEnumerator and GlobalCommitter are just
> >> two
> >> > examples of the demand of such coordination among user defined logics.
> >> > There are other cases that we see in ecosystem projects, such as
> >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> >> >
> >> > Such control plane primitives are critical to the extensibility of a
> >> > project. If we look at other projects, exposing such control plane
> >> logic is
> >> > quite common. For example, Hadoop ended up with exposing YARN as a
> >> public
> >> > API to the users, which is extremely popular. Kafka consumers exposed
> >> the
> >> > consumer group rebalance logic to the users via
> >> ConsumerPartitionAssigner,
> >> > which is also a control plane primitive.
> >> >
> >> > To me it is more important to think about how we can improve the
> >> stability
> >> > of such a control plane mechanism, instead of simply saying no to the
> >> users.
> >> >
> >> >
> >> >
> >> >
> >> > > 2) In addition, I suspect that, over time we will have to implement
> >> all the
> >> > > functionality that regular sources already provide around
> consistency
> >> > > (watermarks, checkpointing) for the PatternProcessorCoordinator,
> too.
> >> >
> >> >
> >> > I think OperatorCoordinator should have a generic communication
> >> mechanism
> >> > for all the operators, not specific to Source. We should probably have
> >> an
> >> > AbstractOperatorCoordinator help dealing with the communication layer,
> >> and
> >> > leave the state maintenance and event handling logic to the user code.
> >> >
> >> >
> >> > > 3) I understand that running on the Jobmanager is easier if you want
> >> to
> >> > > launch a REST server directly. Here my question would be: does this
> >> really
> >> > > need to be solved inside of Flink or couldn't you start a webserver
> >> next to
> >> > > Flink? If we start using the Jobmanager as a REST server users will
> >> expect
> >> > > that e.g. it is highly available and can be load balanced and we
> >> quickly
> >> > > need to think about aspects that we never wanted to think about in
> the
> >> > > context of a Flink Jobmanager.
> >> > >
> >> >
> >> > I think the REST API is just for receiving commands targeting a
> running
> >> > Flink job. If the job fails, the REST API would be useless.
> >> >
> >> >
> >> > > So, can you elaborate a bit more, why a side-input/broadcast stream
> is
> >> > >
> >> > > a) more difficult
> >> > > b) has vague semantics (To me semantics of a stream-stream seem
> >> clearer
> >> > > when it comes to out-of-orderness, late data, reprocessing or batch
> >> > > execution mode.)
> >> >
> >> >
> >> > I do agree that having the user defined control logic defined in the
> JM
> >> > increases the chance of instability. In that case, we may think of
> other
> >> > solutions and I am fully open to that. But the side-input / broadcast
> >> > stream seems more like a bandaid instead of a carefully designed
> control
> >> > plane mechanism.
> >> >
> >> > A decent control plane requires two-way communication, so information
> >> can
> >> > be reported / collected from the entity being controlled, and the
> >> > coordinator / controller can send decisions or commands to the
> entities
> >> > accordingly, just like our TM / JM communication. IIUC, this is not
> >> > achievable with the existing side-input / broadcast stream as both of
> >> them
> >> > are one-way communication mechanisms. For instance, the example I gave
> >> in
> >> > my previous email seems not easily achievable with side-input /
> >> broadcast
> >> > streams: a single invalid pattern detected on a TM can be disabled
> >> > elegantly globally without crashing the entire Flink job.
> >> >
> >> >
> >> > > Cheers,
> >> > >
> >> > > Konstantin
> >> > >
> >> > >
> >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <be...@gmail.com>
> >> wrote:
> >> > >
> >> > > > Hi folks,
> >> > > >
> >> > > > I just finished reading the previous emails. It was a good
> >> discussion.
> >> > > Here
> >> > > > are my two cents:
> >> > > >
> >> > > > *Is OperatorCoordinator a public API?*
> >> > > > Regarding the OperatorCoordinator, although it is marked as
> internal
> >> > > > interface at this point, I intended to make it a public interface
> >> when
> >> > > add
> >> > > > that in FLIP-27. This is a powerful cross-subtask communication
> >> mechanism
> >> > > > that enables many use cases, Source / Sink / TF on Flink / CEP
> here
> >> > > again.
> >> > > > To my understanding, OC was marked as internal because we think it
> >> is not
> >> > > > stable enough yet. We may need to fortify the OperatorEvent
> delivery
> >> > > > semantic a little bit so it works well with checkpoint in general.
> >> > > >
> >> > > > I think it is a valid concern that user code running in JM may
> cause
> >> > > > instability. However, not providing this communication mechanism
> >> only
> >> > > makes
> >> > > > a lot of use case even harder to implement. So it seems that
> having
> >> the
> >> > > OC
> >> > > > exposed to end users brings more benefits than harm to Flink. At
> >> the end
> >> > > of
> >> > > > the day, users have many ways to crash a Flink job if they do not
> >> write
> >> > > > proper code. So making those who know what they do happy seems
> more
> >> > > > important here.
> >> > > >
> >> > > > *OperatorCoordinator V.S. side-input / broadcast stream*
> >> > > > I think both of them can achieve the goal of dynamic patterns. The
> >> main
> >> > > > difference is the extensibility.
> >> > > >
> >> > > > OC is a 2-way communication mechanism, i.e. a subtask can also
> send
> >> > > > OperatorEvent to the coordinator to report its owns status, so
> that
> >> the
> >> > > > coordinator can act accordingly. This is sometimes useful. For
> >> example, a
> >> > > > single invalid pattern can be disabled elegantly without crashing
> >> the
> >> > > > entire Flink job. In the future, if we allow users to send
> external
> >> > > command
> >> > > > to OC via JM, a default self-contained implementation can just
> >> update the
> >> > > > pattern via the REST API without external dependencies.
> >> > > >
> >> > > > Another reason I personally prefer OC is because it is an explicit
> >> > > control
> >> > > > plain mechanism, where as the side-input / broadcast stream has
> are
> >> more
> >> > > > vague semantic.
> >> > > >
> >> > > > Thanks,
> >> > > >
> >> > > > Jiangjie (Becket) Qin
> >> > > >
> >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <dm...@apache.org>
> >> wrote:
> >> > > >
> >> > > > > Hi Yunfeng,
> >> > > > >
> >> > > > > thanks for drafting this FLIP, this will be a great addition
> into
> >> the
> >> > > CEP
> >> > > > > toolbox!
> >> > > > >
> >> > > > > Apart from running user code in JM, which want to avoid in
> >> general, I'd
> >> > > > > have one more another concern about using the
> OperatorCoordinator
> >> and
> >> > > > that
> >> > > > > is re-processing of the historical data. Any thoughts about how
> >> this
> >> > > will
> >> > > > > work with the OC?
> >> > > > >
> >> > > > > I have a slight feeling that a side-input (custom source /
> >> operator +
> >> > > > > broadcast) would a better fit for this case. This would simplify
> >> the
> >> > > > > consistency concerns (watermarks + pushback) and the
> >> re-processing of
> >> > > > > historical data.
> >> > > > >
> >> > > > > Best,
> >> > > > > D.
> >> > > > >
> >> > > > >
> >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> >> > > nicholasjiang@apache.org
> >> > > > >
> >> > > > > wrote:
> >> > > > >
> >> > > > > > Hi Konstantin, Martijn
> >> > > > > >
> >> > > > > > Thanks for the detailed feedback in the discussion. What I
> >> still have
> >> > > > > left
> >> > > > > > to answer/reply to:
> >> > > > > >
> >> > > > > > -- Martijn: Just to be sure, this indeed would mean that if
> for
> >> > > > whatever
> >> > > > > > reason the heartbeat timeout, it would crash the job, right?
> >> > > > > >
> >> > > > > > IMO, if for whatever reason the heartbeat timeout, it couldn't
> >> check
> >> > > > the
> >> > > > > > PatternProcessor consistency between the OperatorCoordinator
> >> and the
> >> > > > > > subtasks so that the job would be crashed.
> >> > > > > >
> >> > > > > > -- Konstantin: What I was concerned about is that we basically
> >> let
> >> > > > users
> >> > > > > > run a UserFunction in the OperatorCoordinator, which it does
> >> not seem
> >> > > > to
> >> > > > > > have been designed for.
> >> > > > > >
> >> > > > > > In general, we have reached an agreement on the design of this
> >> FLIP,
> >> > > > but
> >> > > > > > there are some concerns on the OperatorCoordinator, about
> >> whether
> >> > > > > basically
> >> > > > > > let users run a UserFunction in the OperatorCoordinator is
> >> designed
> >> > > for
> >> > > > > > OperatorCoordinator. We would like to invite Becket Qin who is
> >> the
> >> > > > author
> >> > > > > > of OperatorCoordinator to help us to answer this concern.
> >> > > > > >
> >> > > > > > Best,
> >> > > > > > Nicholas Jiang
> >> > > > > >
> >> > > > > >
> >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> >> > > > > > > Hi all,
> >> > > > > > >
> >> > > > > > > Really like the discussion on this topic moving forward. I
> >> really
> >> > > > think
> >> > > > > > > this feature will be much appreciated by the Flink users.
> >> What I
> >> > > > still
> >> > > > > > have
> >> > > > > > > left to answer/reply to:
> >> > > > > > >
> >> > > > > > > -- Good point. If for whatever reason the different
> >> taskmanagers
> >> > > > can't
> >> > > > > > get
> >> > > > > > > the latest rule, the Operator Coordinator could send a
> >> heartbeat to
> >> > > > all
> >> > > > > > > taskmanagers with the latest rules and check the heartbeat
> >> response
> >> > > > > from
> >> > > > > > > all the taskmanagers whether the latest rules of the
> >> taskmanager is
> >> > > > > equal
> >> > > > > > > to these of the Operator Coordinator.
> >> > > > > > >
> >> > > > > > > Just to be sure, this indeed would mean that if for whatever
> >> reason
> >> > > > the
> >> > > > > > > heartbeat timeout, it would crash the job, right?
> >> > > > > > >
> >> > > > > > > -- We have consided about the solution mentioned above. In
> >> this
> >> > > > > > solution, I
> >> > > > > > > have some questions about how to guarantee the consistency
> of
> >> the
> >> > > > rule
> >> > > > > > > between each TaskManager. By having a coodinator in the
> >> JobManager
> >> > > to
> >> > > > > > > centrally manage the latest rules, the latest rules of all
> >> > > > TaskManagers
> >> > > > > > are
> >> > > > > > > consistent with those of the JobManager, so as to avoid the
> >> > > > > > inconsistencies
> >> > > > > > > that may be encountered in the above solution. Can you
> >> introduce
> >> > > how
> >> > > > > this
> >> > > > > > > solution guarantees the consistency of the rules?
> >> > > > > > >
> >> > > > > > > The consistency that we could guarantee was based on how
> >> often each
> >> > > > > > > TaskManager would do a refresh and how often we would
> accept a
> >> > > > refresh
> >> > > > > to
> >> > > > > > > fail. We set the refresh time to a relatively short one (30
> >> > > seconds)
> >> > > > > and
> >> > > > > > > maximum failures to 3. That meant that we could guarantee
> that
> >> > > rules
> >> > > > > > would
> >> > > > > > > be updated in < 2 minutes or else the job would crash. That
> >> was
> >> > > > > > sufficient
> >> > > > > > > for our use cases. This also really depends on how big your
> >> cluster
> >> > > > > is. I
> >> > > > > > > can imagine that if you have a large scale cluster that you
> >> want to
> >> > > > > run,
> >> > > > > > > you don't want to DDOS the backend system where you have
> your
> >> rules
> >> > > > > > stored.
> >> > > > > > >
> >> > > > > > > -- In summary, the current design is that JobManager tells
> all
> >> > > > > > TaskManagers
> >> > > > > > > the latest rules through OperatorCoodinator, and will
> >> initiate a
> >> > > > > > heartbeat
> >> > > > > > > to check whether the latest rules on each TaskManager are
> >> > > consistent.
> >> > > > > We
> >> > > > > > > will describe how to deal with the Failover scenario in more
> >> detail
> >> > > > on
> >> > > > > > FLIP.
> >> > > > > > >
> >> > > > > > > Thanks for that. I think having the JobManager tell the
> >> > > TaskManagers
> >> > > > > the
> >> > > > > > > applicable rules would indeed end up being the best design.
> >> > > > > > >
> >> > > > > > > -- about the concerns around consistency raised by Martijn:
> I
> >> > > think a
> >> > > > > lot
> >> > > > > > > of those can be mitigated by using an event time timestamp
> >> from
> >> > > which
> >> > > > > the
> >> > > > > > > rules take effect. The reprocessing scenario, for example,
> is
> >> > > covered
> >> > > > > by
> >> > > > > > > this. If a pattern processor should become active as soon as
> >> > > > possible,
> >> > > > > > > there will still be inconsistencies between Taskmanagers,
> but
> >> "as
> >> > > > soon
> >> > > > > as
> >> > > > > > > possible" is vague anyway, which is why I think that's ok.
> >> > > > > > >
> >> > > > > > > I think an event timestamp is indeed a really important one.
> >> We
> >> > > also
> >> > > > > used
> >> > > > > > > that in my previous role, with the ruleActivationTimestamp
> >> compared
> >> > > > to
> >> > > > > > > eventtime (well, actually we used Kafka logAppend time
> because
> >> > > > > > > eventtime wasn't always properly set so we used that time to
> >> > > > overwrite
> >> > > > > > the
> >> > > > > > > eventtime from the event itself).
> >> > > > > > >
> >> > > > > > > Best regards,
> >> > > > > > >
> >> > > > > > > Martijn
> >> > > > > > >
> >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> >> knaufk@apache.org>
> >> > > > > > wrote:
> >> > > > > > >
> >> > > > > > > > Hi Nicholas, Hi Junfeng,
> >> > > > > > > >
> >> > > > > > > > about the concerns around consistency raised by Martijn: I
> >> think
> >> > > a
> >> > > > > lot
> >> > > > > > of
> >> > > > > > > > those can be mitigated by using an event time timestamp
> from
> >> > > which
> >> > > > > the
> >> > > > > > > > rules take effect. The reprocessing scenario, for example,
> >> is
> >> > > > covered
> >> > > > > > by
> >> > > > > > > > this. If a pattern processor should become active as soon
> as
> >> > > > > possible,
> >> > > > > > > > there will still be inconsistencies between Taskmanagers,
> >> but "as
> >> > > > > soon
> >> > > > > > as
> >> > > > > > > > possible" is vague anyway, which is why I think that's ok.
> >> > > > > > > >
> >> > > > > > > > about naming: The naming with "PatternProcessor" sounds
> >> good to
> >> > > me.
> >> > > > > > Final
> >> > > > > > > > nit: I would go for CEP#patternProccessors, which would be
> >> > > > consistent
> >> > > > > > with
> >> > > > > > > > CEP#pattern.
> >> > > > > > > >
> >> > > > > > > > I am not sure about one of the rejected alternatives:
> >> > > > > > > >
> >> > > > > > > > > Have each subtask of an operator make the update on
> their
> >> own
> >> > > > > > > >
> >> > > > > > > > -
> >> > > > > > > >
> >> > > > > > > > It is hard to achieve consistency.
> >> > > > > > > > -
> >> > > > > > > >
> >> > > > > > > > Though the time interval that each subtask makes the
> >> update
> >> > > > can
> >> > > > > > be
> >> > > > > > > > the same, the absolute time they make the update
> >> might be
> >> > > > > > different.
> >> > > > > > > > For
> >> > > > > > > > example, one makes updates at 10:00, 10:05, etc,
> while
> >> > > > another
> >> > > > > > does
> >> > > > > > > > it at
> >> > > > > > > > 10:01, 10:06. In this case the subtasks might never
> >> > > > processing
> >> > > > > > data
> >> > > > > > > > with
> >> > > > > > > > the same set of pattern processors.
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > > I would have thought that it is quite easy to poll for the
> >> rules
> >> > > > from
> >> > > > > > each
> >> > > > > > > > Subtask at *about *the same time. So, this alone does not
> >> seem to
> >> > > > be
> >> > > > > > > > enough to rule out this option. I've looped in David
> >> Moravek to
> >> > > get
> >> > > > > his
> >> > > > > > > > opinion of the additional load imposed on the JM.
> >> > > > > > > >
> >> > > > > > > > Thanks,
> >> > > > > > > >
> >> > > > > > > > Konstantin
> >> > > > > > > >
> >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas Jiang <
> >> > > > > > nicholasjiang@apache.org>
> >> > > > > > > > wrote:
> >> > > > > > > >
> >> > > > > > > > > Hi Yue,
> >> > > > > > > > >
> >> > > > > > > > > Thanks for your feedback of the FLIP. I have addressed
> >> your
> >> > > > > > questions and
> >> > > > > > > > > made a corresponding explanation as follows:
> >> > > > > > > > >
> >> > > > > > > > > -- About Pattern Updating. If we use
> >> > > PatternProcessoerDiscoverer
> >> > > > to
> >> > > > > > > > update
> >> > > > > > > > > the rules, will it increase the load of JM? For example,
> >> if the
> >> > > > > user
> >> > > > > > > > wants
> >> > > > > > > > > the updated rule to take effect immediately,, which
> means
> >> that
> >> > > we
> >> > > > > > need to
> >> > > > > > > > > set a shorter check interval or there is another
> scenario
> >> when
> >> > > > > users
> >> > > > > > > > rarely
> >> > > > > > > > > update the pattern, will the PatternProcessoerDiscoverer
> >> be in
> >> > > > most
> >> > > > > > of
> >> > > > > > > > the
> >> > > > > > > > > time Do useless checks ? Will a lazy update mode could
> be
> >> used,
> >> > > > > > which the
> >> > > > > > > > > pattern only be updated when triggered by the user, and
> do
> >> > > > nothing
> >> > > > > at
> >> > > > > > > > other
> >> > > > > > > > > times?
> >> > > > > > > > >
> >> > > > > > > > > PatternProcessoerDiscoverer is a user-defined interface
> to
> >> > > > discover
> >> > > > > > the
> >> > > > > > > > > PatternProcessor updates. Periodically checking the
> >> > > > > PatternProcessor
> >> > > > > > in
> >> > > > > > > > the
> >> > > > > > > > > database is a implementation of the
> >> PatternProcessoerDiscoverer
> >> > > > > > > > interface,
> >> > > > > > > > > which is that periodically querys all the
> PatternProcessor
> >> > > table
> >> > > > in
> >> > > > > > > > certain
> >> > > > > > > > > interval. This implementation indeeds has the useless
> >> checks,
> >> > > and
> >> > > > > > could
> >> > > > > > > > > directly integrates the changelog of the table. In
> >> addition, in
> >> > > > > > addition
> >> > > > > > > > to
> >> > > > > > > > > the implementation of periodically checking the
> database,
> >> there
> >> > > > are
> >> > > > > > other
> >> > > > > > > > > implementations such as the PatternProcessor that
> provides
> >> > > > Restful
> >> > > > > > > > services
> >> > > > > > > > > to receive updates.
> >> > > > > > > > >
> >> > > > > > > > > -- I still have some confusion about how Key Generating
> >> > > > Opertator
> >> > > > > > and
> >> > > > > > > > > CepOperator (Pattern Matching & Processing Operator)
> work
> >> > > > together.
> >> > > > > > If
> >> > > > > > > > > there are N PatternProcessors, will the Key Generating
> >> > > Opertator
> >> > > > > > > > generate N
> >> > > > > > > > > keyedStreams, and then N CepOperator would process each
> >> Key
> >> > > > > > separately ?
> >> > > > > > > > Or
> >> > > > > > > > > every CepOperator Task would process all patterns, if
> so,
> >> does
> >> > > > the
> >> > > > > > key
> >> > > > > > > > type
> >> > > > > > > > > in each PatternProcessor need to be the same?
> >> > > > > > > > >
> >> > > > > > > > > Firstly the Pattern Matching & Processing Operator is
> not
> >> the
> >> > > > > > CepOperator
> >> > > > > > > > > at present, because CepOperator mechanism is based on
> the
> >> > > > NFAState.
> >> > > > > > > > > Secondly if there are N PatternProcessors, the Key
> >> Generating
> >> > > > > > Opertator
> >> > > > > > > > > combines all the keyedStreams with keyBy() operation,
> >> thus the
> >> > > > > > Pattern
> >> > > > > > > > > Matching & Processing Operator would process all the
> >> patterns.
> >> > > In
> >> > > > > > other
> >> > > > > > > > > words, the KeySelector of the PatternProcessor is used
> >> for the
> >> > > > Key
> >> > > > > > > > > Generating Opertator, and the Pattern and
> >> > > PatternProceessFunction
> >> > > > > of
> >> > > > > > the
> >> > > > > > > > > PatternProcessor are used for the Pattern Matching &
> >> Processing
> >> > > > > > Operator.
> >> > > > > > > > > Lastly the key type in each PatternProcessor is the
> same,
> >> > > > regarded
> >> > > > > as
> >> > > > > > > > > Object type.
> >> > > > > > > > >
> >> > > > > > > > > -- Maybe need to pay attention to it when implementing
> it
> >> .If
> >> > > > some
> >> > > > > > > > Pattern
> >> > > > > > > > > has been removed or updated, will the partially matched
> >> results
> >> > > > in
> >> > > > > > > > > StateBackend would be clean up or We rely on state ttl
> to
> >> clean
> >> > > > up
> >> > > > > > these
> >> > > > > > > > > expired states.
> >> > > > > > > > >
> >> > > > > > > > > If certain Pattern has been removed or updated, the
> >> partially
> >> > > > > matched
> >> > > > > > > > > results in StateBackend would be clean up until the next
> >> > > > > checkpoint.
> >> > > > > > The
> >> > > > > > > > > partially matched result doesn't depend on the state ttl
> >> of the
> >> > > > > > > > > StateBackend.
> >> > > > > > > > >
> >> > > > > > > > > 4. Will the PatternProcessorManager keep all the active
> >> > > > > > PatternProcessor
> >> > > > > > > > > in memory? We have also Support Multiple Rule and
> Dynamic
> >> Rule
> >> > > > > > Changing.
> >> > > > > > > > > But we are facing such a problem, some users’ usage
> >> scenarios
> >> > > are
> >> > > > > > that
> >> > > > > > > > they
> >> > > > > > > > > want to have their own pattern for each user_id, which
> >> means
> >> > > that
> >> > > > > > there
> >> > > > > > > > > could be thousands of patterns, which would make the
> >> > > performance
> >> > > > of
> >> > > > > > > > Pattern
> >> > > > > > > > > Matching very poor. We are also trying to solve this
> >> problem.
> >> > > > > > > > >
> >> > > > > > > > > The PatternProcessorManager keeps all the active
> >> > > PatternProcessor
> >> > > > > in
> >> > > > > > > > > memory. For scenarios that they want to have their own
> >> pattern
> >> > > > for
> >> > > > > > each
> >> > > > > > > > > user_id, IMO, is it possible to reduce the fine-grained
> >> pattern
> >> > > > of
> >> > > > > > > > > PatternProcessor to solve the performance problem of the
> >> > > Pattern
> >> > > > > > > > Matching,
> >> > > > > > > > > for example, a pattern corresponds to a group of users?
> >> The
> >> > > > > scenarios
> >> > > > > > > > > mentioned above need to be solved by case by case.
> >> > > > > > > > >
> >> > > > > > > > > Best,
> >> > > > > > > > > Nicholas Jiang
> >> > > > > > > > >
> >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> >> > > > > > > > > > Glad to see the Community's progress in Flink CEP.
> After
> >> > > > reading
> >> > > > > > this
> >> > > > > > > > > Flip,
> >> > > > > > > > > > I have few questions, would you please take a look ?
> >> > > > > > > > > >
> >> > > > > > > > > > 1. About Pattern Updating. If we use
> >> > > > PatternProcessoerDiscoverer
> >> > > > > to
> >> > > > > > > > > update
> >> > > > > > > > > > the rules, will it increase the load of JM? For
> >> example, if
> >> > > the
> >> > > > > > user
> >> > > > > > > > > wants
> >> > > > > > > > > > the updated rule to take effect immediately,, which
> >> means
> >> > > that
> >> > > > we
> >> > > > > > need
> >> > > > > > > > to
> >> > > > > > > > > > set a shorter check interval or there is another
> >> scenario
> >> > > when
> >> > > > > > users
> >> > > > > > > > > > rarely update the pattern, will the
> >> > > PatternProcessoerDiscoverer
> >> > > > > be
> >> > > > > > in
> >> > > > > > > > > most
> >> > > > > > > > > > of the time Do useless checks ? Will a lazy update
> mode
> >> could
> >> > > > be
> >> > > > > > used,
> >> > > > > > > > > > which the pattern only be updated when triggered by
> the
> >> user,
> >> > > > and
> >> > > > > > do
> >> > > > > > > > > > nothing at other times ?
> >> > > > > > > > > >
> >> > > > > > > > > > 2. I still have some confusion about how Key
> >> Generating
> >> > > > > > Opertator and
> >> > > > > > > > > > CepOperator (Pattern Matching & Processing Operator)
> >> work
> >> > > > > > together. If
> >> > > > > > > > > > there are N PatternProcessors, will the Key Generating
> >> > > > Opertator
> >> > > > > > > > > generate N
> >> > > > > > > > > > keyedStreams, and then N CepOperator would process
> each
> >> Key
> >> > > > > > separately
> >> > > > > > > > ?
> >> > > > > > > > > Or
> >> > > > > > > > > > every CepOperator Task would process all patterns, if
> >> so,
> >> > > does
> >> > > > > the
> >> > > > > > key
> >> > > > > > > > > type
> >> > > > > > > > > > in each PatternProcessor need to be the same ?
> >> > > > > > > > > >
> >> > > > > > > > > > 3. Maybe need to pay attention to it when implementing
> >> it .If
> >> > > > > some
> >> > > > > > > > > Pattern
> >> > > > > > > > > > has been removed or updateed ,will the partially
> >> matched
> >> > > > results
> >> > > > > > in
> >> > > > > > > > > > StateBackend would be clean up or We rely on state ttl
> >> to
> >> > > clean
> >> > > > > up
> >> > > > > > > > these
> >> > > > > > > > > > expired states.
> >> > > > > > > > > >
> >> > > > > > > > > > 4. Will the PatternProcessorManager keep all the
> active
> >> > > > > > > > PatternProcessor
> >> > > > > > > > > in
> >> > > > > > > > > > memory ? We have also Support Multiple Rule and
> Dynamic
> >> Rule
> >> > > > > > Changing .
> >> > > > > > > > > > But we are facing such a problem, some users’ usage
> >> scenarios
> >> > > > are
> >> > > > > > that
> >> > > > > > > > > they
> >> > > > > > > > > > want to have their own pattern for each user_id, which
> >> means
> >> > > > that
> >> > > > > > there
> >> > > > > > > > > > could be thousands of patterns, which would make the
> >> > > > performance
> >> > > > > of
> >> > > > > > > > > Pattern
> >> > > > > > > > > > Matching very poor. We are also trying to solve this
> >> problem.
> >> > > > > > > > > >
> >> > > > > > > > > > Yunfeng Zhou <fl...@gmail.com>
> >> 于2021年12月10日周五
> >> > > > > 19:16写道：
> >> > > > > > > > > >
> >> > > > > > > > > > > Hi all，
> >> > > > > > > > > > >
> >> > > > > > > > > > > I'm opening this thread to propose the design to
> >> support
> >> > > > > multiple
> >> > > > > > > > rule
> >> > > > > > > > > &
> >> > > > > > > > > > > dynamic rule changing in the Flink-CEP project, as
> >> > > described
> >> > > > in
> >> > > > > > > > > FLIP-200
> >> > > > > > > > > > > [1]
> >> > > > > > > > > > > .
> >> > > > > > > > > > >
> >> > > > > > > > > > > Currently Flink CEP only supports having a single
> >> pattern
> >> > > > > inside
> >> > > > > > a
> >> > > > > > > > > > > CepOperator and does not support changing the
> pattern
> >> > > > > > dynamically. In
> >> > > > > > > > > order
> >> > > > > > > > > > > to reduce resource consumption and to experience
> >> shorter
> >> > > > > downtime
> >> > > > > > > > > during
> >> > > > > > > > > > > pattern updates, there is a growing need in the
> >> production
> >> > > > > > > > environment
> >> > > > > > > > > that
> >> > > > > > > > > > > expects CEP to support having multiple patterns in
> one
> >> > > > operator
> >> > > > > > and
> >> > > > > > > > to
> >> > > > > > > > > > > support dynamically changing them. Therefore I
> >> propose to
> >> > > add
> >> > > > > > certain
> >> > > > > > > > > > > infrastructure as described in FLIP-200 to support
> >> these
> >> > > > > > > > > functionalities.
> >> > > > > > > > > > >
> >> > > > > > > > > > > Please feel free to reply to this email thread.
> >> Looking
> >> > > > forward
> >> > > > > > to
> >> > > > > > > > your
> >> > > > > > > > > > > feedback!
> >> > > > > > > > > > >
> >> > > > > > > > > > > [1]
> >> > > > > > > > > > >
> >> > > > > > > > >
> >> > > > > > > >
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >>
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> >> > > > > > > > > > >
> >> > > > > > > > > > > Best regards,
> >> > > > > > > > > > >
> >> > > > > > > > > > > Yunfeng
> >> > > > > > > > > > >
> >> > > > > > > > > >
> >> > > > > > > > >
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > > --
> >> > > > > > > >
> >> > > > > > > > Konstantin Knauf
> >> > > > > > > >
> >> > > > > > > > https://twitter.com/snntrable
> >> > > > > > > >
> >> > > > > > > > https://github.com/knaufk
> >> > > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> > >
> >> > > --
> >> > >
> >> > > Konstantin Knauf
> >> > >
> >> > > https://twitter.com/snntrable
> >> > >
> >> > > https://github.com/knaufk
> >> > >
> >> >
> >>
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Becket Qin <be...@gmail.com>.
Hi folks,
Till and I had an offline discussion about this FLIP. And it looks that
currently OC is still coupled with the Source operator in some cases. So it
is not really ready for the CEP use case at this point. In order to provide
the CEP dynamic pattern update feature to the users, at the moment a
connected stream seems the only viable solution. So here is what we agreed:
1. For this FLIP, we will use the connected stream to update the dynamic
pattern. API wise, it probably means there will be a method in the CEP
class such as
public static <IN, OUT> DataStream<OUT> patternProcessors(
DataStream<IN> input, DataStream<CEPCommand> commandStream)
{...}
This means a proper pattern update command API needs to be designed so
users can provide the pattern update commands in the command stream.
2. Meanwhile, we will improve the OC protocol to make it generic to support
arbitrary operators. After that, we will revisit the option of CEP and may
add a new API to CEP which may look like something below.
public static <IN, OUT> DataStream<OUT> patternProcessors(
DataStream<IN> input, PatternProcessorDiscovererFactory<IN,
OUT> factory) {...}
And in this FLIP, we will mention the OC effort in the future work part to
let the users be aware of the potential future addition to the CEP API for
dynamic pattern update. So for people who are willing to wait for the OC
based API, they may choose to hold on a little bit.
If later on in the future, we see one of the two API flavors become
dominant, we can deprecate the other.
Some other things that may worth mentioning are:
1. The command streams will likely just use the processing/ingestion time
instead of event time to avoid unexpected watermark pauses.
2. In order to reprocess a record stream and produce repeatable result, it
is recommended to fully load the pattern change log before start processing
the record stream.
Thanks,
Jiangjie (Becket) Qin
On Thu, Jan 6, 2022 at 3:51 PM Till Rohrmann <tr...@apache.org> wrote:
> Hi Becket,
>
> I might be missing something but having to define interfaces/formats for
> the CEP patterns should be necessary for either approach. The OC approach
> needs to receive and understand the pattern data from somewhere as well and
> will probably also have to deal with evolving formats. Hence, I believe
> that this work wouldn't be wasted.
>
> I might misjudge the willingness of our users to do some extra set up work,
> but I think that some of them would already be happy with state 1.
>
> My understanding so far was that the OC approach also requires the CEP
> operator infrastructure (making the operator accept new patterns) work that
> I proposed to do as a first step. The only difference is where the new
> patterns/commands are coming from. If we design this correctly, then this
> should change only very little depending on whether you read from a
> side-input or from an OC.
>
> Another benefit of downscoping the FLIP is to make it more realistic to be
> completed. Smaller and incremental steps are usually easier to realize. If
> we now say that this FLIP requires a general purpose user controlled
> control plane that gives you hard guarantees, then I am pretty sure that
> this will take at least half a year.
>
> Cheers,
> Till
>
> On Thu, Jan 6, 2022 at 4:45 AM Becket Qin <be...@gmail.com> wrote:
>
> > Thanks for the explanation, Till. I like the idea, but have a question
> > about the first step.
> >
> > After the first step, would users be able to actually use the dynamic
> > patterns in CEP?
> >
> > In the first step you mentioned, the commands and formats for a new CEP
> > pattern seem related to how users would ingest the commands. If we go
> with
> > the OC, these commands and formats would become internal interfaces. The
> > end users would just use the REST API, or in the beginning, implement a
> > Java plugin of dynamic pattern provider. In this case our focus would be
> on
> > designing a good plugin interface. On the other hand, if we go with the
> > side-input, users would need to know the command format so they can send
> > the commands to the CEP operator. Therefore we need to think about stuff
> > like versioning, request validation and backwards compatibility.
> >
> > Also, because the public interface is all about how the users can ingest
> > the dynamic patterns. It seems we still need to figure that out before we
> > can conclude the FLIP.
> >
> > Assuming the first step closes this FLIP and after that users would be
> able
> > to use the CEP dynamic pattern, are you suggesting the following?
> >
> > 1. We will design the commands and format of CEP dynamic pattern, and
> also
> > how CEP operators take them into effect. This design would assume that
> > users can send the commands directly to the CEP operator via side-input.
> So
> > the protocol would take versioning and format evolution into account.
> After
> > the first step, the users CAN make dynamic pattern work with the help
> from
> > some external dependencies and maintenance effort.
> >
> > 2. Discuss about a control plane from the use case of CEP dynamic
> pattern,
> > and let CEP dynamic pattern use that control plane if we eventually think
> > that is the right way to go.
> >
> > Assuming that we are not going to stop after step 1 is done, will the end
> > state be that the CEP dynamic pattern supports both approaches? It is not
> > clear to me how this would work. For example, will a pattern ingested
> from
> > side-input be managed by OC as well? If more and more users pick the more
> > ergonomic way, would the side-input option just die out? In that case,
> will
> > we deprecate that?
> >
> > My main concern is that the time and work we invest in step 1 will be
> > thrown away. Not only that, at the end of step 1, in order to actually
> use
> > the feature and make it production ready, there is a lot of work for the
> > users to do. All that work may also become in vain. So it would be good
> if
> > we can avoid that by having a clean approach to begin with. What do you
> > think?
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> >
> > On Wed, Jan 5, 2022 at 11:35 PM Till Rohrmann <tr...@apache.org>
> > wrote:
> >
> > > I think I would scope the effort slightly differently. Note that I
> might
> > be
> > > missing some requirements or overlook something.
> > >
> > > 1. Enable Flink to support CEP dynamic patterns
> > >
> > > Here I would define the commands and formats for a new CEP pattern.
> Then
> > I
> > > would extend the CEP operator to understand these commands so that we
> can
> > > change the CEP patterns dynamically. This should give the building
> blocks
> > > to set up a job where you can change the CEP patterns by reading from
> an
> > > arbitrary side input the CEP pattern commands. Note that it will be the
> > > responsibility of the user to ingest the data somehow. This is nothing
> > > Flink is concerned with at this time.
> > >
> > > 2. Think about how to make the CEP dynamic pattern feature more
> ergonomic
> > >
> > > Here we can pick up the discussion about OC and having a REST ingestion
> > > endpoint in Flink vs. offering tools that live outside of Flink
> itself. I
> > > could imagine that this could become a separate small project that
> builds
> > > upon Flink, for example.
> > >
> > > Cheers,
> > > Till
> > >
> > > On Wed, Jan 5, 2022 at 2:19 PM Becket Qin <be...@gmail.com>
> wrote:
> > >
> > > > Hi Till,
> > > >
> > > > Thanks for the prompt reply. Like you said, we are indeed using the
> > > dynamic
> > > > CEP pattern use case to test the existing primitives in Flink to see
> if
> > > > they can meet the requirements. I fully understand the concern of
> > > > exposing OC as a user interface. Meanwhile I see CEP dynamic patterns
> > as
> > > a
> > > > good opportunity to battle test and enhance the OC as a user facing
> > > control
> > > > plane which is currently missing. After all, there is no better
> person
> > > than
> > > > ourselves to try it out first.
> > > >
> > > > It is not clear to me whether it is worth continuing the effort of
> > > > supporting dynamic CEP pattern without concluding the control plane
> > > > discussion. Let's say we have a CEP job reading from Kafka. To make
> > this
> > > > work with side-input, a few things need to be done.
> > > >
> > > > 1. In order to support dynamic patterns, users would create
> another
> > > > Kafka topic as side-input to receive dynamic patterns.
> > > > 2. In order to insert dynamic patterns, users would use a separate
> > web
> > > > server that is provided by us as a separate tool. The web server
> > takes
> > > > http
> > > > requests and sends dynamic pattern records to Kafka via a Kafka
> sink
> > > > (using
> > > > a KafkaProducer is likely simpler here, though).
> > > > 3. Regarding querying the running dynamic patterns, given Kafka is
> > not
> > > > queryable, users would probably introduce a database and insert
> the
> > > > patterns there so they can query the running patterns. Maybe this
> > > could
> > > > be
> > > > done by the CEP operator side-output, so there is less chance of
> > > > inconsistency between Kafka and the database.
> > > > 4. If the Flink job is to be stopped, the dynamic pattern Kafka
> > topic
> > > > needs to be deleted, the companion web server also needs to be
> > stopped
> > > > (assuming it is not shared with other CEP jobs), and the database
> > > table
> > > > storing the dynamic pattern needs to be dropped.
> > > >
> > > > Please correct me if I misunderstood something, but this seems quite
> > > > involved. Moreover, all the work here is going to be thrown away
> after
> > we
> > > > have OC as a decent user facing control plane in place. And we will
> > > likely
> > > > have a backwards incompatible API change here. Given that, I am
> > wondering
> > > > if we should wait until the OC discussion concludes before moving on
> > with
> > > > the dynamic patterns?
> > > >
> > > > Thanks,
> > > >
> > > > Jiangjie (Becket) Qin
> > > >
> > > >
> > > >
> > > > On Wed, Jan 5, 2022 at 5:53 PM Till Rohrmann <tr...@apache.org>
> > > wrote:
> > > >
> > > > > Thanks for the detailed explanation Becket.
> > > > >
> > > > > Do you think that an additional dependency is a deal breaker for
> > people
> > > > to
> > > > > use dynamic CEP patterns? At the very least people have to operate
> > some
> > > > > kind of storage/queue system from which the CEP job can read
> anyway.
> > > > Maybe
> > > > > it could be good enough to provide a REST endpoint (as a separate
> > tool)
> > > > > that can be instantiated with a Flink sink to ingest REST requests
> > > > > into some queue. A general concern I have is that by making the JM
> a
> > > REST
> > > > > ingestion point for data will push another responsibility to Flink
> > and
> > > > > increase the surface area further.
> > > > >
> > > > > For how to handle data that cannot be processed by patterns, I
> think
> > > > there
> > > > > also exist other solutions. I could imagine that users could define
> > > > > different failover strategies. E.g. one could simply ignore the
> > record,
> > > > the
> > > > > pattern could get deactivated on the affected TM or the processing
> > > fails.
> > > > >
> > > > > Maybe we are coupling the dynamic CEP pattern effort too much on
> > where
> > > > the
> > > > > new patterns come from. Maybe we can split these efforts into
> > > supporting
> > > > > dynamic CEP patterns on the TM reading from some source and then
> fork
> > > off
> > > > > the discussion about introducing a user controlled control plane to
> > > > Flink.
> > > > > That way we wouldn't block this effort and could discuss more about
> > the
> > > > > exact properties such a user control plane would need to have. What
> > do
> > > > you
> > > > > think?
> > > > >
> > > > > Cheers,
> > > > > Till
> > > > >
> > > > > On Wed, Jan 5, 2022 at 7:18 AM Becket Qin <be...@gmail.com>
> > > wrote:
> > > > >
> > > > > > Hi Till,
> > > > > >
> > > > > > Thanks for the comments and questions. To be clear, I am not
> saying
> > > > that
> > > > > > the side-input stream does not work for the dynamic pattern
> update
> > > use
> > > > > > case. But I think OC is a better solution. The design goal for
> CEP
> > > > > dynamic
> > > > > > pattern is not only make it work, but also make it user friendly
> > and
> > > > > > extensible. So as a user, I expect the following:
> > > > > >
> > > > > > - Use CEP with dynamic pattern update without depending on
> external
> > > > > > systems. e.g. updating the pattern by directly talking to the
> Flink
> > > job
> > > > > > itself.
> > > > > > - Some sort of isolation between patterns. e.g. a pattern update
> > > > failure
> > > > > > won't cause other running patterns to fail.
> > > > > > - Easy to query the currently running patterns in the Flink job.
> > > > > > - Extensible to add new features. e.g. apply some pattern to a
> > subset
> > > > of
> > > > > > subtasks. Disable dynamic pattern update during a service window,
> > > etc.
> > > > > >
> > > > > > It looks to me that OC is a more promising way to to achieve the
> > > above.
> > > > > >
> > > > > > Please also see the reply to your questions inline below.
> > > > > >
> > > > > > > You mentioned that a TM might find out that a pattern is
> invalid
> > > and
> > > > > then
> > > > > > > it could use the 2-way communication with the JM to tell the
> > other
> > > > TMs
> > > > > > that
> > > > > > > the pattern is invalid. How exactly would a TM detect that a
> > > pattern
> > > > is
> > > > > > > invalid at data processing time? And assuming that this is
> > possible
> > > > > for a
> > > > > > > single TM, why can't the other TMs not detect this problem? Is
> it
> > > > > because
> > > > > > > the validity of patterns might depend on data that is different
> > > > between
> > > > > > > TMs?
> > > > > >
> > > > > >
> > > > > > Yes, the TMs are processing different records, so some may
> > encounter
> > > > > issue
> > > > > > while others are running fine, for example, a field may be
> missing
> > > > from a
> > > > > > record while the pattern requires it. Even if all the TMs have
> > > detected
> > > > > the
> > > > > > problem, without a channel to report back the issue, the only
> thing
> > > TMs
> > > > > can
> > > > > > do is either to throw exception and stop processing.
> > > > > >
> > > > > > You also mentioned that deep-learning-on-flink could benefit from
> > an
> > > OC
> > > > > > > control plane but I couldn't find the referenced link. Would
> > > > > > > deep-learning-on-flink like to use OCs as a kind of parameter
> > > server?
> > > > > > Could
> > > > > > > you elaborate on deep-learning-on-flink's usage of such a
> > feature?
> > > > > >
> > > > > >
> > > > > > deep-learning-on-flink[1] has a general ML cluster abstraction
> that
> > > can
> > > > > run
> > > > > > TF / PyTorch etc. This cluster has a ML master role to manage the
> > > > > > liveliness of all the ML workers which are python processes
> running
> > > > > > side-by-side with TMs. The ML workers can be PS or Worker of
> > > > TensorFlow.
> > > > > > For example, if 10 TF worker and 5 TF PS nodes are needed, a
> Flink
> > > UDF
> > > > > > operator of parallelism 10 and a Flink Source operator with
> > > parallelism
> > > > > = 5
> > > > > > will be created to run the TF worker and TF PS respectively. All
> > the
> > > 15
> > > > > > nodes running either PS or Worker are managed by the ML master.
> > Prior
> > > > to
> > > > > > OC, the implementation was having a Source operator with
> > parallelism
> > > =
> > > > 1
> > > > > to
> > > > > > run the master; let the ML workers register themselves to the an
> > > > external
> > > > > > ZK so the master can discover them. So basically users have to
> > build
> > > > > their
> > > > > > own control plane. With OC, at very least, we no longer need ZK
> > > > anymore.
> > > > > >
> > > > > > Concerning reprocessing command history and repeatable processing
> > > > > results I
> > > > > > > think there is actually quite a big difference between using a
> > > Flink
> > > > > > source
> > > > > > > vs. offering a REST server that can receive command that are
> > > > > distributed
> > > > > > > via the OCs. In the former case we can rely on the external
> > system
> > > to
> > > > > > > persist commands whereas in the latter approach we/users have
> to
> > > > > > implement
> > > > > > > a storage solution on their own (in the simplest case users
> will
> > > > > probably
> > > > > > > store everything in state which might grow indefinitely if
> stored
> > > as
> > > > a
> > > > > > > changelog).
> > > > > >
> > > > > >
> > > > > > It is true that a Flink Source is easier to provide a change log
> of
> > > > > > patterns. But there are also downsides. The most prominent one is
> > > that
> > > > in
> > > > > > order to update the dynamic pattern, users have to run an
> external
> > > > system
> > > > > > for the source to read. Or users have to implement a REST Source
> > > taking
> > > > > > command directly like a web server. In that case, the service
> > > discovery
> > > > > is
> > > > > > again a problem and needs external dependency.
> > > > > > On the other hand, it is not so difficult for OC to store a
> change
> > > log
> > > > > > history. Assuming there are 100 pattern updates / day for a CEP
> job
> > > and
> > > > > one
> > > > > > year of history should be stored. Let's say each pattern change
> log
> > > > entry
> > > > > > is 1K bytes. The pattern update change log for the entire year is
> > > just
> > > > 34
> > > > > > MB, which seems quite small. And users can also query the
> patterns
> > in
> > > > > > effect via the same endpoint. I think this would provide a good
> > > > > out-of-box
> > > > > > experience in the vast majority of cases. No external
> dependencies
> > > and
> > > > a
> > > > > > single REST endpoint. In rare cases where there is a large amount
> > of
> > > > > > pattern update log. External systems can still be leveraged. One
> > > > > potential
> > > > > > issue might be that a command that has been received but not
> > > > checkpointed
> > > > > > yet may got lost if the job fails over. This can be mitigated by
> > > > allowing
> > > > > > OC to ask JM to trigger a checkpoint (not there yet but may worth
> > > > > > thinking), or simply introduce a *PendingCommit* state for a
> > pattern
> > > > > > indicating it's not committed yet. In the worst case, we can
> always
> > > > > > fallback to store patterns in external systems such as a
> database.
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Jiangjie (Becket) Qin
> > > > > >
> > > > > > [1]
> > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
> > > > > >
> > > > > >
> > > > > > On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <
> trohrmann@apache.org
> > >
> > > > > wrote:
> > > > > >
> > > > > > > Hi Becket,
> > > > > > >
> > > > > > > Thanks for the explanation. While I do agree that a general
> 2-way
> > > > > > > communication pattern would be nice to have, I also believe
> that
> > > this
> > > > > > > approach is probably at least one magnitude more complex to
> > realize
> > > > > than
> > > > > > > the side-input approach. Therefore, I really would like to
> > > understand
> > > > > why
> > > > > > > such a mechanism is required for the CEP use case.
> > > > > > >
> > > > > > > You mentioned that a TM might find out that a pattern is
> invalid
> > > and
> > > > > then
> > > > > > > it could use the 2-way communication with the JM to tell the
> > other
> > > > TMs
> > > > > > that
> > > > > > > the pattern is invalid. How exactly would a TM detect that a
> > > pattern
> > > > is
> > > > > > > invalid at data processing time? And assuming that this is
> > possible
> > > > > for a
> > > > > > > single TM, why can't the other TMs not detect this problem? Is
> it
> > > > > because
> > > > > > > the validity of patterns might depend on data that is different
> > > > between
> > > > > > > TMs?
> > > > > > >
> > > > > > > You also mentioned that deep-learning-on-flink could benefit
> from
> > > an
> > > > OC
> > > > > > > control plane but I couldn't find the referenced link. Would
> > > > > > > deep-learning-on-flink like to use OCs as a kind of parameter
> > > server?
> > > > > > Could
> > > > > > > you elaborate on deep-learning-on-flink's usage of such a
> > feature?
> > > > > > >
> > > > > > > Concerning reprocessing command history and repeatable
> processing
> > > > > > results I
> > > > > > > think there is actually quite a big difference between using a
> > > Flink
> > > > > > source
> > > > > > > vs. offering a REST server that can receive command that are
> > > > > distributed
> > > > > > > via the OCs. In the former case we can rely on the external
> > system
> > > to
> > > > > > > persist commands whereas in the latter approach we/users have
> to
> > > > > > implement
> > > > > > > a storage solution on their own (in the simplest case users
> will
> > > > > probably
> > > > > > > store everything in state which might grow indefinitely if
> stored
> > > as
> > > > a
> > > > > > > changelog).
> > > > > > >
> > > > > > > Cheers,
> > > > > > > Till
> > > > > > >
> > > > > > > On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <
> becket.qin@gmail.com>
> > > > > wrote:
> > > > > > >
> > > > > > > > Hi David,
> > > > > > > >
> > > > > > > > Thanks for sharing your thoughts. Some quick reply to your
> > > > comments:
> > > > > > > >
> > > > > > > > We're still talking about the "web server based"
> > > > > > > > > pattern_processor_discoverer, but what about other use
> cases?
> > > One
> > > > > of
> > > > > > my
> > > > > > > > big
> > > > > > > > > concerns is that user's can not really reuse any part of
> the
> > > > Flink
> > > > > > > > > ecosystem to implement the discovery logic. For example if
> > they
> > > > > want
> > > > > > to
> > > > > > > > > read patterns from Kafka topic, they need to roll their own
> > > > > > discoverer
> > > > > > > > > based on the vanilla Kafka client. If we're talking about
> > > > > > > extensibility,
> > > > > > > > > should we also make sure that the existing primitives can
> be
> > > > > reused?
> > > > > > > >
> > > > > > > >
> > > > > > > > KafkaSource is actually more complicated than vanilla
> > > KafkaConsumer
> > > > > > from
> > > > > > > > the perspective of consuming Kafka messages. The KafkaSource
> > just
> > > > > helps
> > > > > > > > make it easier for Flink jobs to process these messages. In
> > fact,
> > > > > > > > KafkaConsumer is more powerful than KafkaSource in terms of
> > > talking
> > > > > to
> > > > > > > > Kafka. So we are comparing [KafkaConsumer +
> > OperatorCoordinator]
> > > > and
> > > > > > > > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> > > > > > > >
> > > > > > > > This can be done for the side-input as well by filtering
> > invalid
> > > > > > patterns
> > > > > > > > > before the broadcast. You can also send the invalid
> patterns
> > to
> > > > any
> > > > > > > side
> > > > > > > > > output you want. I have a feeling that we're way too
> attached
> > > to
> > > > > the
> > > > > > > REST
> > > > > > > > > server use case in this discussion. I agree that for that
> > case,
> > > > > this
> > > > > > > > > solution is the most straightforward one.
> > > > > > > >
> > > > > > > >
> > > > > > > > Depending on whether the invalidity is discovered in pattern
> > > > > definition
> > > > > > > > time or data processing time. e.g. A valid pattern with
> invalid
> > > > data
> > > > > > > which
> > > > > > > > fails to process can only be detected in data processing
> time.
> > So
> > > > the
> > > > > > > > pattern won't be filtered out before the broadcast.
> > > > > > > >
> > > > > > > > I agree that 2-way communication in the "data-flow like" API
> is
> > > > > tricky,
> > > > > > > > > because it requires cycles / iterations, which are still
> not
> > > > really
> > > > > > > > solved
> > > > > > > > > (for a good reason, it's really tough nut to crack). This
> > makes
> > > > me
> > > > > > > think
> > > > > > > > > that the OC may be bit of a "incomplete" workaround for not
> > > > having
> > > > > > > fully
> > > > > > > > > working support for iterations.
> > > > > > > >
> > > > > > > >
> > > > > > > > For example I'm not really confident that the checkpointing
> of
> > > the
> > > > OC
> > > > > > > works
> > > > > > > > > correctly right now, because it doesn't seem to require
> > > > checkpoint
> > > > > > > > barrier
> > > > > > > > > alignment as the regular stream inputs. We also don't have
> a
> > > > proper
> > > > > > > > support
> > > > > > > > > for watermarking (this is again tricky, because of the
> > cycle).
> > > > > > > >
> > > > > > > >
> > > > > > > > If we decide to go down this road, should we first address
> some
> > > of
> > > > > > these
> > > > > > > > > limitations?
> > > > > > > >
> > > > > > > > I agree. OC is proven to be useful and we should think about
> > how
> > > to
> > > > > > > enhance
> > > > > > > > it instead of not using it.
> > > > > > > >
> > > > > > > > If I understand that correctly, this means only the LATEST
> > state
> > > of
> > > > > the
> > > > > > > > > patterns (in other words - patterns that are currently in
> > use).
> > > > Is
> > > > > > this
> > > > > > > > > really sufficient for historical re-processing? Can someone
> > for
> > > > > > example
> > > > > > > > > want re-process the data in more of a "temporal join"
> > fashion?
> > > > Also
> > > > > > > AFAIK
> > > > > > > > > historical processing in combination with "coordinator
> > > > checkpoints"
> > > > > > is
> > > > > > > > not
> > > > > > > > > really something that we currently support of the box, are
> > > there
> > > > > any
> > > > > > > > plans
> > > > > > > > > on tackling this (my other concern is that this should not
> go
> > > > > against
> > > > > > > the
> > > > > > > > > "unified batch & stream processing" efforts)?
> > > > > > > >
> > > > > > > > I think in this case, the state would contain the entire
> > pattern
> > > > > update
> > > > > > > > history. Not the final state, but the change log. In fact, it
> > is
> > > > not
> > > > > > > > possible to guarantee the correct result unless you have the
> > > entire
> > > > > > > change
> > > > > > > > log. Even with side-input, there still could be late arrivals
> > in
> > > > the
> > > > > > > > pattern update stream, and the only way to correct it is to
> > > either
> > > > > have
> > > > > > > all
> > > > > > > > the data reprocessed (with all the pattern change log loaded
> > > > upfront)
> > > > > > or
> > > > > > > > having retraction support.
> > > > > > > >
> > > > > > > > I can imagine that if this should be a concern, we could move
> > the
> > > > > > > execution
> > > > > > > > > of the OC to the task managers. This also makes me thing,
> > that
> > > we
> > > > > > > > shouldn't
> > > > > > > > > make any strong assumptions that the OC will always run in
> > the
> > > > > > > JobManager
> > > > > > > > > (this is especially relevant for the embedded web-server
> use
> > > > case).
> > > > > > > >
> > > > > > > > This is a very good point. I think we should do this. The
> > reason
> > > OC
> > > > > is
> > > > > > in
> > > > > > > > JM is based on the assumption that control plane usually have
> > > > little
> > > > > > > > traffic. But if that is not the case, we should move the OC
> out
> > > of
> > > > > JM,
> > > > > > > > maybe to TM.
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > I think the key topic we are discussing is what the Flink
> > control
> > > > > plane
> > > > > > > > should look like, and CEP is just an example use case. There
> > are
> > > > > > > basically
> > > > > > > > two options:
> > > > > > > >
> > > > > > > > 1. Using the side-input / broadcast stream
> > > > > > > > 2. Using the OperatorCoordinator.
> > > > > > > >
> > > > > > > > Although we are having this discussion under the context of
> > > > > supporting
> > > > > > > CEP
> > > > > > > > dynamic pattern update, it would be really helpful to reach
> > > > agreement
> > > > > > on
> > > > > > > > the design principle in general of how Flink should handle
> > > similar
> > > > > > > external
> > > > > > > > control demands, a.k.a how to provide a decent control plane
> in
> > > > Flink
> > > > > > to
> > > > > > > > the users.
> > > > > > > >
> > > > > > > > Here is my take on these two options, based on the
> requirements
> > > of
> > > > a
> > > > > > > > control plane.
> > > > > > > >
> > > > > > > > *Communication Requirements*
> > > > > > > > Flink has two kinds of control planes - in-band and
> > out-of-band.
> > > > > > > > In-band control plane is like watermark and checkpoint
> marker.
> > It
> > > > > > > requires
> > > > > > > > the entire DAG to be in a consistent state, so the control
> > > messages
> > > > > > flow
> > > > > > > > with the data in one direction. This is a one-way control
> flow.
> > > > > > > > Examples of out-of-band control plane is OC and JM/TM
> > > > communication.
> > > > > > They
> > > > > > > > do not require a global consistency or awareness across the
> > > entire
> > > > > DAG.
> > > > > > > >
> > > > > > > > Before OC, neither of these two kinds of control plain was
> > > exposed
> > > > to
> > > > > > the
> > > > > > > > users. OC allows the users to leverage the out-of-band
> control
> > > > plane
> > > > > so
> > > > > > > > they can coordinate across subtasks. This is a more widely
> used
> > > > > control
> > > > > > > > flow from user defined operator perspective which requires
> > 2-way
> > > > > > > > communication.
> > > > > > > >
> > > > > > > > - side-input stream is one-way communication. Moreover, I
> > > don't
> > > > > > think
> > > > > > > > iteration is the right way to address this. Unlike the
> > > > abstraction
> > > > > > of
> > > > > > > > data
> > > > > > > > processing which is a DAG, the control plane may require
> > > > > > communication
> > > > > > > > between arbitrary two operators in different orders. Using
> > > > > > iterations
> > > > > > > > may
> > > > > > > > end up with an explosion of feedback edges that are not
> only
> > > > > > > > complicated to
> > > > > > > > express, but also hard to debug and maintain.
> > > > > > > > - OC provides a decent 2-way communication mechanism.
> > > > > > > >
> > > > > > > >
> > > > > > > > *Cost for low traffic use case*
> > > > > > > > An important difference between data channel and control
> > channel
> > > is
> > > > > > > traffic
> > > > > > > > pattern. Unlike data plane, the control plane is usually idle
> > for
> > > > the
> > > > > > > vast
> > > > > > > > majority of the time with occasional control messages.
> > > > > > > >
> > > > > > > > - One argument to use the side-input / broadcast stream
> was
> > > that
> > > > > > users
> > > > > > > > can reuse the existing connectors. However, most Flink
> > sources
> > > > are
> > > > > > > > designed
> > > > > > > > to handle large throughput of traffic that maintains all
> the
> > > > > > threads,
> > > > > > > > network connections, etc. Not to say the external
> resources
> > > such
> > > > > as
> > > > > > > > Kafka
> > > > > > > > topics to store the commands.
> > > > > > > > - OC can have a much lower constant cost.
> > > > > > > >
> > > > > > > >
> > > > > > > > *Easy to use*
> > > > > > > > Personally speaking, I think the most simple and
> user-friendly
> > > > > > interface
> > > > > > > is
> > > > > > > > a REST API that accepts control commands.
> > > > > > > >
> > > > > > > > - One proposal at this point is to have a separate web
> > server
> > > > > > > > independent of the Flink job. In that case, should users
> > > > implement
> > > > > > > that
> > > > > > > > web
> > > > > > > > server? In order to pass the command to the Flink job,
> does
> > > that
> > > > > > mean
> > > > > > > > users
> > > > > > > > should implement a Flink source that can read the commands
> > > from
> > > > > the
> > > > > > > web
> > > > > > > > server? Or the web server would send the command to
> > something
> > > > like
> > > > > > > Kafka
> > > > > > > > and let the Flink side-input read from there. There seems
> to
> > > be
> > > > a
> > > > > > lot
> > > > > > > > for
> > > > > > > > the users to do. And it seems an unnecessarily complicated
> > > > system
> > > > > to
> > > > > > > > build
> > > > > > > > to send occasional control messages to a Flink job.
> > > > > > > > - OC can simply be reached via the JM REST API.
> > > > > > > > - e.g.
> > http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > > > > > > > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx>
> > > would
> > > > > > simply
> > > > > > > > send the Content to the OC of OP_NAME.
> > > > > > > >
> > > > > > > > *Work well with checkpoints*
> > > > > > > >
> > > > > > > > - side-input streams works well with checkpoint, thanks to
> > its
> > > > > > > > compatibility to the DAG abstraction.
> > > > > > > > - The OperatorCoordinator requires more careful design to
> > work
> > > > > well
> > > > > > > with
> > > > > > > > checkpoints. The complexity mostly comes from the 2-way
> > > > > > communication.
> > > > > > > > At
> > > > > > > > this point the OperatorCoordinator message delivery
> semantic
> > > may
> > > > > not
> > > > > > > be
> > > > > > > > as
> > > > > > > > robust as side-input streams. However, I think this is
> > mainly
> > > > due
> > > > > to
> > > > > > > > potential bugs in implementation instead of fundamental
> > design
> > > > > > > problems.
> > > > > > > > Basically the checkpoint semantic should be:
> > > > > > > > - The JM will first checkpoint all the
> > OperatorCoordinator,
> > > > > more
> > > > > > > > specifically for each OperatorCoordinator,
> > > > > > > > - 1) JM blocks the input queue to stop receiving new
> > > > events
> > > > > > from
> > > > > > > > the subtasks.
> > > > > > > > - 2) let all the operator coordinator finish
> > processing
> > > > all
> > > > > > the
> > > > > > > > pending events in the OC input queue.
> > > > > > > > - 3) flush the OC output queue until all the events
> > sent
> > > > are
> > > > > > > > acknowledged.
> > > > > > > > - 3) unblock the input queue, but block the output
> > queue
> > > > > until
> > > > > > > all
> > > > > > > > the subtasks of the OC finish checkpoints.
> > > > > > > > - The JM starts a normal checkpoint starting from the
> > > Source.
> > > > > > > > - If an operator has a coordinator, and it has sent
> > some
> > > > > > events
> > > > > > > to
> > > > > > > > the OC but has not been acknowledged. These events
> > need
> > > to
> > > > > be
> > > > > > > > put into the
> > > > > > > > subtasks' checkpoint.
> > > > > > > > - After all the subtasks of an operator finishes
> > > checkpoint,
> > > > > the
> > > > > > > > output queue of the corresponding OC can be unblocked.
> > > > > > > > It looks that the above protocol would let OC have a clear
> > > > > > checkpoint
> > > > > > > > semantic. And this complexity seems must for 2-way
> > > > communication.
> > > > > I
> > > > > > > > think
> > > > > > > > we are able to hide the above protocol from users by
> having
> > an
> > > > > > > abstract
> > > > > > > > OC
> > > > > > > > implementation.
> > > > > > > >
> > > > > > > >
> > > > > > > > *Reprocess command history and repeatable processing results*
> > > > > > > > This seems not something generally required for a control
> > plane.
> > > > But
> > > > > if
> > > > > > > the
> > > > > > > > control plane changes the data processing behavior, there
> might
> > > be
> > > > > some
> > > > > > > use
> > > > > > > > case. Just like the CEP pattern update. In order to do this,
> > > users
> > > > > will
> > > > > > > > need to provide a full command history to the operators. That
> > > > > consists
> > > > > > of
> > > > > > > > two steps:
> > > > > > > >
> > > > > > > > 1. get the full command history. (Flink Source V.S.
> Custom
> > > way
> > > > to
> > > > > > > > retrieve command history.)
> > > > > > > > 2. send them to the operators. (Side-input V.S.
> OC/Operator
> > > > > > > > communication)l
> > > > > > > >
> > > > > > > > I actually don't feel much difference between these two
> > options.
> > > I
> > > > am
> > > > > > not
> > > > > > > > sure if a Flink source is necessarily simpler than the user
> > > > > implemented
> > > > > > > > logic. For example, if all the changes are just written in a
> > > > database
> > > > > > > > table. From the user's perspective, I feel fine with querying
> > the
> > > > DB
> > > > > by
> > > > > > > > myself using something like JDBC (or use KafkaConsumer to
> read
> > > the
> > > > > > > pattern
> > > > > > > > history from a Kafka topic) and send all the pattern change
> > > history
> > > > > to
> > > > > > > the
> > > > > > > > operators before they start to process the actual events.
> > > > > > > >
> > > > > > > > *Stability impact to the Flink Job*
> > > > > > > > I agree this is a valid concern. There is only one JM and
> > > currently
> > > > > OC
> > > > > > > runs
> > > > > > > > there, which may potentially cause JM crash and result in job
> > > > > failure.
> > > > > > > > Running in TM may have a less impact. So I think it makes
> sense
> > > to
> > > > > run
> > > > > > OC
> > > > > > > > in TM. However, this is more of how we can implement OC to
> make
> > > it
> > > > > more
> > > > > > > > robust. It does not forfeit the other semantic and user
> > > experience
> > > > > > > benefits
> > > > > > > > mentioned above.
> > > > > > > >
> > > > > > > >
> > > > > > > > To sum up:
> > > > > > > > 1. Regardless of whether CEP chooses OC or side-input
> stream, a
> > > > > decent
> > > > > > > > 2-way communication control plane seems really helpful and
> has
> > > been
> > > > > > > proven
> > > > > > > > by quite a few existing use cases. To me the question is how
> to
> > > > make
> > > > > it
> > > > > > > > more robust, not whether we should use it or not.
> > > > > > > > 2. As for CEP, if we assume OC will be robust enough,
> > personally
> > > I
> > > > > feel
> > > > > > > OC
> > > > > > > > is a better fit than side-input mainly because of the
> > simplicity
> > > > and
> > > > > > > > extensibility.
> > > > > > > >
> > > > > > > > Thanks,
> > > > > > > >
> > > > > > > > Jiangjie (Becket) Qin
> > > > > > > >
> > > > > > > >
> > > > > > > > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <
> dmvk@apache.org
> > >
> > > > > wrote:
> > > > > > > >
> > > > > > > > > Hi all,
> > > > > > > > >
> > > > > > > > > sorry for the late reply, vacation season ;) I'm still not
> > 100%
> > > > > sold
> > > > > > on
> > > > > > > > > choosing the OC for this use-case, but on the other hand I
> > > don't
> > > > > have
> > > > > > > > > strong arguments against it. Few more questions / thoughts:
> > > > > > > > >
> > > > > > > > > We're still talking about the "web server based"
> > > > > > > > > pattern_processor_discoverer, but what about other use
> cases?
> > > One
> > > > > of
> > > > > > my
> > > > > > > > big
> > > > > > > > > concerns is that user's can not really reuse any part of
> the
> > > > Flink
> > > > > > > > > ecosystem to implement the discovery logic. For example if
> > they
> > > > > want
> > > > > > to
> > > > > > > > > read patterns from Kafka topic, they need to roll their own
> > > > > > discoverer
> > > > > > > > > based on the vanilla Kafka client. If we're talking about
> > > > > > > extensibility,
> > > > > > > > > should we also make sure that the existing primitives can
> be
> > > > > reused?
> > > > > > > > >
> > > > > > > > > For instance, the example I gave in my previous email seems
> > not
> > > > > > easily
> > > > > > > > > > achievable with side-input / broadcast streams: a single
> > > > invalid
> > > > > > > > pattern
> > > > > > > > > > detected on a TM can be disabled elegantly globally
> without
> > > > > > crashing
> > > > > > > > the
> > > > > > > > > > entire Flink job.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > This can be done for the side-input as well by filtering
> > > invalid
> > > > > > > patterns
> > > > > > > > > before the broadcast. You can also send the invalid
> patterns
> > to
> > > > any
> > > > > > > side
> > > > > > > > > output you want. I have a feeling that we're way too
> attached
> > > to
> > > > > the
> > > > > > > REST
> > > > > > > > > server use case in this discussion. I agree that for that
> > case,
> > > > > this
> > > > > > > > > solution is the most straightforward one.
> > > > > > > > >
> > > > > > > > > OC is a 2-way communication mechanism, i.e. a subtask can
> > also
> > > > send
> > > > > > > > > > OperatorEvent to the coordinator to report its owns
> status,
> > > so
> > > > > that
> > > > > > > the
> > > > > > > > > > coordinator can act accordingly.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > I agree that 2-way communication in the "data-flow like"
> API
> > is
> > > > > > tricky,
> > > > > > > > > because it requires cycles / iterations, which are still
> not
> > > > really
> > > > > > > > solved
> > > > > > > > > (for a good reason, it's really tough nut to crack). This
> > makes
> > > > me
> > > > > > > think
> > > > > > > > > that the OC may be bit of a "incomplete" workaround for not
> > > > having
> > > > > > > fully
> > > > > > > > > working support for iterations.
> > > > > > > > >
> > > > > > > > > For example I'm not really confident that the checkpointing
> > of
> > > > the
> > > > > OC
> > > > > > > > works
> > > > > > > > > correctly right now, because it doesn't seem to require
> > > > checkpoint
> > > > > > > > barrier
> > > > > > > > > alignment as the regular stream inputs. We also don't have
> a
> > > > proper
> > > > > > > > support
> > > > > > > > > for watermarking (this is again tricky, because of the
> > cycle).
> > > > > > > > >
> > > > > > > > > If we decide to go down this road, should we first address
> > some
> > > > of
> > > > > > > these
> > > > > > > > > limitations?
> > > > > > > > >
> > > > > > > > > OperatorCoordinator will checkpoint the full amount of
> > > > > > PatternProcessor
> > > > > > > > > > data. For the reprocessing of historical data, you can
> read
> > > the
> > > > > > > > > > PatternProcessor snapshots saved by this checkpoint from
> a
> > > > > certain
> > > > > > > > > > historical checkpoint, and then recreate the historical
> > data
> > > > > > through
> > > > > > > > > these
> > > > > > > > > > PatternProcessor snapshots.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > If I understand that correctly, this means only the LATEST
> > > state
> > > > of
> > > > > > the
> > > > > > > > > patterns (in other words - patterns that are currently in
> > use).
> > > > Is
> > > > > > this
> > > > > > > > > really sufficient for historical re-processing? Can someone
> > for
> > > > > > example
> > > > > > > > > want re-process the data in more of a "temporal join"
> > fashion?
> > > > Also
> > > > > > > AFAIK
> > > > > > > > > historical processing in combination with "coordinator
> > > > checkpoints"
> > > > > > is
> > > > > > > > not
> > > > > > > > > really something that we currently support of the box, are
> > > there
> > > > > any
> > > > > > > > plans
> > > > > > > > > on tackling this (my other concern is that this should not
> go
> > > > > against
> > > > > > > the
> > > > > > > > > "unified batch & stream processing" efforts)?
> > > > > > > > >
> > > > > > > > > I do agree that having the user defined control logic
> defined
> > > in
> > > > > the
> > > > > > JM
> > > > > > > > > > increases the chance of instability.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > I can imagine that if this should be a concern, we could
> move
> > > the
> > > > > > > > execution
> > > > > > > > > of the OC to the task managers. This also makes me thing,
> > that
> > > we
> > > > > > > > shouldn't
> > > > > > > > > make any strong assumptions that the OC will always run in
> > the
> > > > > > > JobManager
> > > > > > > > > (this is especially relevant for the embedded web-server
> use
> > > > case).
> > > > > > > > >
> > > > > > > > > If an agreement is reached on OperatorCoodinator, I will
> > start
> > > > the
> > > > > > > voting
> > > > > > > > > > thread.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > As for the vote, I'd would be great if we can wait until
> the
> > > next
> > > > > > week
> > > > > > > as
> > > > > > > > > many people took vacation until end of the year.
> > > > > > > > >
> > > > > > > > > Overall, I really like the feature, this will be a great
> > > addition
> > > > > to
> > > > > > > > Flink.
> > > > > > > > >
> > > > > > > > > Best,
> > > > > > > > > D.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <
> > > > > > martijn@ververica.com
> > > > > > > >
> > > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > Hi all,
> > > > > > > > > >
> > > > > > > > > > I can understand the need for a control plane mechanism.
> > I'm
> > > > not
> > > > > > the
> > > > > > > > > > technical go-to person for questions on the
> > > > OperatorCoordinator,
> > > > > > but
> > > > > > > I
> > > > > > > > > > would expect that we could offer those interfaces from
> > Flink
> > > > but
> > > > > > > > > shouldn't
> > > > > > > > > > recommend running user-code in the JobManager itself. I
> > think
> > > > the
> > > > > > > user
> > > > > > > > > code
> > > > > > > > > > (like a webserver) should run outside of Flink (like via
> a
> > > > > sidecar)
> > > > > > > and
> > > > > > > > > use
> > > > > > > > > > only the provided interfaces to communicate.
> > > > > > > > > >
> > > > > > > > > > I would like to get @David Morávek <dm...@apache.org>
> > opinion
> > > > on
> > > > > > the
> > > > > > > > > > technical part.
> > > > > > > > > >
> > > > > > > > > > Best regards,
> > > > > > > > > >
> > > > > > > > > > Martijn
> > > > > > > > > >
> > > > > > > > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> > > > > > > nicholasjiang@apache.org
> > > > > > > > >
> > > > > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > >> Hi Konstantin, Becket, Martijn,
> > > > > > > > > >>
> > > > > > > > > >> Thanks for sharing your feedback. What other concerns do
> > you
> > > > > have
> > > > > > > > about
> > > > > > > > > >> OperatorCoodinator? If an agreement is reached on
> > > > > > > OperatorCoodinator,
> > > > > > > > I
> > > > > > > > > >> will start the voting thread.
> > > > > > > > > >>
> > > > > > > > > >> Best,
> > > > > > > > > >> Nicholas Jiang
> > > > > > > > > >>
> > > > > > > > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > > > > > > > >> > Hi Konstantin,
> > > > > > > > > >> >
> > > > > > > > > >> > Thanks for sharing your thoughts. Please see the reply
> > > > inline
> > > > > > > below.
> > > > > > > > > >> >
> > > > > > > > > >> > Thanks,
> > > > > > > > > >> >
> > > > > > > > > >> > Jiangjie (Becket) Qin
> > > > > > > > > >> >
> > > > > > > > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> > > > > > > knaufk@apache.org
> > > > > > > > >
> > > > > > > > > >> wrote:
> > > > > > > > > >> >
> > > > > > > > > >> > > Hi Becket, Hi Nicholas,
> > > > > > > > > >> > >
> > > > > > > > > >> > > Thanks for joining the discussion.
> > > > > > > > > >> > >
> > > > > > > > > >> > > 1 ) Personally, I would argue that we should only
> run
> > > user
> > > > > > code
> > > > > > > in
> > > > > > > > > the
> > > > > > > > > >> > > Jobmanager/Jobmaster if we can not avoid it. It
> seems
> > > > wrong
> > > > > to
> > > > > > > me
> > > > > > > > to
> > > > > > > > > >> > > encourage users to e.g. run a webserver on the
> > > Jobmanager,
> > > > > or
> > > > > > > > > >> continuously
> > > > > > > > > >> > > read patterns from a Kafka Topic on the Jobmanager,
> > but
> > > > both
> > > > > > of
> > > > > > > > > these
> > > > > > > > > >> I see
> > > > > > > > > >> > > happening with the current design. We've had lots of
> > > > issues
> > > > > > with
> > > > > > > > > >> > > classloading leaks and other stability issues on the
> > > > > > Jobmanager
> > > > > > > > and
> > > > > > > > > >> making
> > > > > > > > > >> > > this more complicated, if there is another way,
> seems
> > > > > > > unnecessary.
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > I think the key question here is what primitive does
> > Flink
> > > > > > provide
> > > > > > > > to
> > > > > > > > > >> > facilitate the user implementation of their own
> control
> > > > logic
> > > > > /
> > > > > > > > > control
> > > > > > > > > >> > plane? It looks that previously, Flink assumes that
> all
> > > the
> > > > > user
> > > > > > > > logic
> > > > > > > > > >> is
> > > > > > > > > >> > just data processing logic without any control /
> > > > coordination
> > > > > > > > > >> requirements.
> > > > > > > > > >> > However, it turns out that a decent control plane
> > > > abstraction
> > > > > is
> > > > > > > > > >> required
> > > > > > > > > >> > in association with the data processing logic in many
> > > cases,
> > > > > > > > including
> > > > > > > > > >> > Source / Sink and other user defined operators in
> > general.
> > > > The
> > > > > > > fact
> > > > > > > > > >> that we
> > > > > > > > > >> > ended up with adding the SplitEnumerator and
> > > GlobalCommitter
> > > > > are
> > > > > > > > just
> > > > > > > > > >> two
> > > > > > > > > >> > examples of the demand of such coordination among user
> > > > defined
> > > > > > > > logics.
> > > > > > > > > >> > There are other cases that we see in ecosystem
> projects,
> > > > such
> > > > > as
> > > > > > > > > >> > deep-learning-on-flink[1]. Now we see this again in
> CEP.
> > > > > > > > > >> >
> > > > > > > > > >> > Such control plane primitives are critical to the
> > > > > extensibility
> > > > > > > of a
> > > > > > > > > >> > project. If we look at other projects, exposing such
> > > control
> > > > > > plane
> > > > > > > > > >> logic is
> > > > > > > > > >> > quite common. For example, Hadoop ended up with
> exposing
> > > > YARN
> > > > > > as a
> > > > > > > > > >> public
> > > > > > > > > >> > API to the users, which is extremely popular. Kafka
> > > > consumers
> > > > > > > > exposed
> > > > > > > > > >> the
> > > > > > > > > >> > consumer group rebalance logic to the users via
> > > > > > > > > >> ConsumerPartitionAssigner,
> > > > > > > > > >> > which is also a control plane primitive.
> > > > > > > > > >> >
> > > > > > > > > >> > To me it is more important to think about how we can
> > > improve
> > > > > the
> > > > > > > > > >> stability
> > > > > > > > > >> > of such a control plane mechanism, instead of simply
> > > saying
> > > > no
> > > > > > to
> > > > > > > > the
> > > > > > > > > >> users.
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > > 2) In addition, I suspect that, over time we will
> have
> > > to
> > > > > > > > implement
> > > > > > > > > >> all the
> > > > > > > > > >> > > functionality that regular sources already provide
> > > around
> > > > > > > > > consistency
> > > > > > > > > >> > > (watermarks, checkpointing) for the
> > > > > > PatternProcessorCoordinator,
> > > > > > > > > too.
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > I think OperatorCoordinator should have a generic
> > > > > communication
> > > > > > > > > >> mechanism
> > > > > > > > > >> > for all the operators, not specific to Source. We
> should
> > > > > > probably
> > > > > > > > have
> > > > > > > > > >> an
> > > > > > > > > >> > AbstractOperatorCoordinator help dealing with the
> > > > > communication
> > > > > > > > layer,
> > > > > > > > > >> and
> > > > > > > > > >> > leave the state maintenance and event handling logic
> to
> > > the
> > > > > user
> > > > > > > > code.
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > > 3) I understand that running on the Jobmanager is
> > easier
> > > > if
> > > > > > you
> > > > > > > > want
> > > > > > > > > >> to
> > > > > > > > > >> > > launch a REST server directly. Here my question
> would
> > > be:
> > > > > does
> > > > > > > > this
> > > > > > > > > >> really
> > > > > > > > > >> > > need to be solved inside of Flink or couldn't you
> > start
> > > a
> > > > > > > > webserver
> > > > > > > > > >> next to
> > > > > > > > > >> > > Flink? If we start using the Jobmanager as a REST
> > server
> > > > > users
> > > > > > > > will
> > > > > > > > > >> expect
> > > > > > > > > >> > > that e.g. it is highly available and can be load
> > > balanced
> > > > > and
> > > > > > we
> > > > > > > > > >> quickly
> > > > > > > > > >> > > need to think about aspects that we never wanted to
> > > think
> > > > > > about
> > > > > > > in
> > > > > > > > > the
> > > > > > > > > >> > > context of a Flink Jobmanager.
> > > > > > > > > >> > >
> > > > > > > > > >> >
> > > > > > > > > >> > I think the REST API is just for receiving commands
> > > > targeting
> > > > > a
> > > > > > > > > running
> > > > > > > > > >> > Flink job. If the job fails, the REST API would be
> > > useless.
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > > So, can you elaborate a bit more, why a
> > > > side-input/broadcast
> > > > > > > > stream
> > > > > > > > > is
> > > > > > > > > >> > >
> > > > > > > > > >> > > a) more difficult
> > > > > > > > > >> > > b) has vague semantics (To me semantics of a
> > > stream-stream
> > > > > > seem
> > > > > > > > > >> clearer
> > > > > > > > > >> > > when it comes to out-of-orderness, late data,
> > > reprocessing
> > > > > or
> > > > > > > > batch
> > > > > > > > > >> > > execution mode.)
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > I do agree that having the user defined control logic
> > > > defined
> > > > > in
> > > > > > > the
> > > > > > > > > JM
> > > > > > > > > >> > increases the chance of instability. In that case, we
> > may
> > > > > think
> > > > > > of
> > > > > > > > > other
> > > > > > > > > >> > solutions and I am fully open to that. But the
> > side-input
> > > /
> > > > > > > > broadcast
> > > > > > > > > >> > stream seems more like a bandaid instead of a
> carefully
> > > > > designed
> > > > > > > > > control
> > > > > > > > > >> > plane mechanism.
> > > > > > > > > >> >
> > > > > > > > > >> > A decent control plane requires two-way communication,
> > so
> > > > > > > > information
> > > > > > > > > >> can
> > > > > > > > > >> > be reported / collected from the entity being
> > controlled,
> > > > and
> > > > > > the
> > > > > > > > > >> > coordinator / controller can send decisions or
> commands
> > to
> > > > the
> > > > > > > > > entities
> > > > > > > > > >> > accordingly, just like our TM / JM communication.
> IIUC,
> > > this
> > > > > is
> > > > > > > not
> > > > > > > > > >> > achievable with the existing side-input / broadcast
> > stream
> > > > as
> > > > > > both
> > > > > > > > of
> > > > > > > > > >> them
> > > > > > > > > >> > are one-way communication mechanisms. For instance,
> the
> > > > > example
> > > > > > I
> > > > > > > > gave
> > > > > > > > > >> in
> > > > > > > > > >> > my previous email seems not easily achievable with
> > > > side-input
> > > > > /
> > > > > > > > > >> broadcast
> > > > > > > > > >> > streams: a single invalid pattern detected on a TM can
> > be
> > > > > > disabled
> > > > > > > > > >> > elegantly globally without crashing the entire Flink
> > job.
> > > > > > > > > >> >
> > > > > > > > > >> >
> > > > > > > > > >> > > Cheers,
> > > > > > > > > >> > >
> > > > > > > > > >> > > Konstantin
> > > > > > > > > >> > >
> > > > > > > > > >> > >
> > > > > > > > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> > > > > > > becket.qin@gmail.com
> > > > > > > > >
> > > > > > > > > >> wrote:
> > > > > > > > > >> > >
> > > > > > > > > >> > > > Hi folks,
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > I just finished reading the previous emails. It
> was
> > a
> > > > good
> > > > > > > > > >> discussion.
> > > > > > > > > >> > > Here
> > > > > > > > > >> > > > are my two cents:
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > *Is OperatorCoordinator a public API?*
> > > > > > > > > >> > > > Regarding the OperatorCoordinator, although it is
> > > marked
> > > > > as
> > > > > > > > > internal
> > > > > > > > > >> > > > interface at this point, I intended to make it a
> > > public
> > > > > > > > interface
> > > > > > > > > >> when
> > > > > > > > > >> > > add
> > > > > > > > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> > > > > > > communication
> > > > > > > > > >> mechanism
> > > > > > > > > >> > > > that enables many use cases, Source / Sink / TF on
> > > > Flink /
> > > > > > CEP
> > > > > > > > > here
> > > > > > > > > >> > > again.
> > > > > > > > > >> > > > To my understanding, OC was marked as internal
> > because
> > > > we
> > > > > > > think
> > > > > > > > it
> > > > > > > > > >> is not
> > > > > > > > > >> > > > stable enough yet. We may need to fortify the
> > > > > OperatorEvent
> > > > > > > > > delivery
> > > > > > > > > >> > > > semantic a little bit so it works well with
> > checkpoint
> > > > in
> > > > > > > > general.
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > I think it is a valid concern that user code
> running
> > > in
> > > > JM
> > > > > > may
> > > > > > > > > cause
> > > > > > > > > >> > > > instability. However, not providing this
> > communication
> > > > > > > mechanism
> > > > > > > > > >> only
> > > > > > > > > >> > > makes
> > > > > > > > > >> > > > a lot of use case even harder to implement. So it
> > > seems
> > > > > that
> > > > > > > > > having
> > > > > > > > > >> the
> > > > > > > > > >> > > OC
> > > > > > > > > >> > > > exposed to end users brings more benefits than
> harm
> > to
> > > > > > Flink.
> > > > > > > At
> > > > > > > > > >> the end
> > > > > > > > > >> > > of
> > > > > > > > > >> > > > the day, users have many ways to crash a Flink job
> > if
> > > > they
> > > > > > do
> > > > > > > > not
> > > > > > > > > >> write
> > > > > > > > > >> > > > proper code. So making those who know what they do
> > > happy
> > > > > > seems
> > > > > > > > > more
> > > > > > > > > >> > > > important here.
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > *OperatorCoordinator V.S. side-input / broadcast
> > > stream*
> > > > > > > > > >> > > > I think both of them can achieve the goal of
> dynamic
> > > > > > patterns.
> > > > > > > > The
> > > > > > > > > >> main
> > > > > > > > > >> > > > difference is the extensibility.
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > OC is a 2-way communication mechanism, i.e. a
> > subtask
> > > > can
> > > > > > also
> > > > > > > > > send
> > > > > > > > > >> > > > OperatorEvent to the coordinator to report its
> owns
> > > > > status,
> > > > > > so
> > > > > > > > > that
> > > > > > > > > >> the
> > > > > > > > > >> > > > coordinator can act accordingly. This is sometimes
> > > > useful.
> > > > > > For
> > > > > > > > > >> example, a
> > > > > > > > > >> > > > single invalid pattern can be disabled elegantly
> > > without
> > > > > > > > crashing
> > > > > > > > > >> the
> > > > > > > > > >> > > > entire Flink job. In the future, if we allow users
> > to
> > > > send
> > > > > > > > > external
> > > > > > > > > >> > > command
> > > > > > > > > >> > > > to OC via JM, a default self-contained
> > implementation
> > > > can
> > > > > > just
> > > > > > > > > >> update the
> > > > > > > > > >> > > > pattern via the REST API without external
> > > dependencies.
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > Another reason I personally prefer OC is because
> it
> > is
> > > > an
> > > > > > > > explicit
> > > > > > > > > >> > > control
> > > > > > > > > >> > > > plain mechanism, where as the side-input /
> broadcast
> > > > > stream
> > > > > > > has
> > > > > > > > > are
> > > > > > > > > >> more
> > > > > > > > > >> > > > vague semantic.
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > Thanks,
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > Jiangjie (Becket) Qin
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> > > > > > > dmvk@apache.org>
> > > > > > > > > >> wrote:
> > > > > > > > > >> > > >
> > > > > > > > > >> > > > > Hi Yunfeng,
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > thanks for drafting this FLIP, this will be a
> > great
> > > > > > addition
> > > > > > > > > into
> > > > > > > > > >> the
> > > > > > > > > >> > > CEP
> > > > > > > > > >> > > > > toolbox!
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > Apart from running user code in JM, which want
> to
> > > > avoid
> > > > > in
> > > > > > > > > >> general, I'd
> > > > > > > > > >> > > > > have one more another concern about using the
> > > > > > > > > OperatorCoordinator
> > > > > > > > > >> and
> > > > > > > > > >> > > > that
> > > > > > > > > >> > > > > is re-processing of the historical data. Any
> > > thoughts
> > > > > > about
> > > > > > > > how
> > > > > > > > > >> this
> > > > > > > > > >> > > will
> > > > > > > > > >> > > > > work with the OC?
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > I have a slight feeling that a side-input
> (custom
> > > > > source /
> > > > > > > > > >> operator +
> > > > > > > > > >> > > > > broadcast) would a better fit for this case.
> This
> > > > would
> > > > > > > > simplify
> > > > > > > > > >> the
> > > > > > > > > >> > > > > consistency concerns (watermarks + pushback) and
> > the
> > > > > > > > > >> re-processing of
> > > > > > > > > >> > > > > historical data.
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > Best,
> > > > > > > > > >> > > > > D.
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > > > > > > > >> > > nicholasjiang@apache.org
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > wrote:
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > > > > Hi Konstantin, Martijn
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > Thanks for the detailed feedback in the
> > > discussion.
> > > > > > What I
> > > > > > > > > >> still have
> > > > > > > > > >> > > > > left
> > > > > > > > > >> > > > > > to answer/reply to:
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > -- Martijn: Just to be sure, this indeed would
> > > mean
> > > > > that
> > > > > > > if
> > > > > > > > > for
> > > > > > > > > >> > > > whatever
> > > > > > > > > >> > > > > > reason the heartbeat timeout, it would crash
> the
> > > > job,
> > > > > > > right?
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > IMO, if for whatever reason the heartbeat
> > timeout,
> > > > it
> > > > > > > > couldn't
> > > > > > > > > >> check
> > > > > > > > > >> > > > the
> > > > > > > > > >> > > > > > PatternProcessor consistency between the
> > > > > > > OperatorCoordinator
> > > > > > > > > >> and the
> > > > > > > > > >> > > > > > subtasks so that the job would be crashed.
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > -- Konstantin: What I was concerned about is
> > that
> > > we
> > > > > > > > basically
> > > > > > > > > >> let
> > > > > > > > > >> > > > users
> > > > > > > > > >> > > > > > run a UserFunction in the OperatorCoordinator,
> > > which
> > > > > it
> > > > > > > does
> > > > > > > > > >> not seem
> > > > > > > > > >> > > > to
> > > > > > > > > >> > > > > > have been designed for.
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > In general, we have reached an agreement on
> the
> > > > design
> > > > > > of
> > > > > > > > this
> > > > > > > > > >> FLIP,
> > > > > > > > > >> > > > but
> > > > > > > > > >> > > > > > there are some concerns on the
> > > OperatorCoordinator,
> > > > > > about
> > > > > > > > > >> whether
> > > > > > > > > >> > > > > basically
> > > > > > > > > >> > > > > > let users run a UserFunction in the
> > > > > OperatorCoordinator
> > > > > > is
> > > > > > > > > >> designed
> > > > > > > > > >> > > for
> > > > > > > > > >> > > > > > OperatorCoordinator. We would like to invite
> > > Becket
> > > > > Qin
> > > > > > > who
> > > > > > > > is
> > > > > > > > > >> the
> > > > > > > > > >> > > > author
> > > > > > > > > >> > > > > > of OperatorCoordinator to help us to answer
> this
> > > > > > concern.
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > Best,
> > > > > > > > > >> > > > > > Nicholas Jiang
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > > > > > > > >> > > > > > > Hi all,
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > Really like the discussion on this topic
> > moving
> > > > > > > forward. I
> > > > > > > > > >> really
> > > > > > > > > >> > > > think
> > > > > > > > > >> > > > > > > this feature will be much appreciated by the
> > > Flink
> > > > > > > users.
> > > > > > > > > >> What I
> > > > > > > > > >> > > > still
> > > > > > > > > >> > > > > > have
> > > > > > > > > >> > > > > > > left to answer/reply to:
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > -- Good point. If for whatever reason the
> > > > different
> > > > > > > > > >> taskmanagers
> > > > > > > > > >> > > > can't
> > > > > > > > > >> > > > > > get
> > > > > > > > > >> > > > > > > the latest rule, the Operator Coordinator
> > could
> > > > > send a
> > > > > > > > > >> heartbeat to
> > > > > > > > > >> > > > all
> > > > > > > > > >> > > > > > > taskmanagers with the latest rules and check
> > the
> > > > > > > heartbeat
> > > > > > > > > >> response
> > > > > > > > > >> > > > > from
> > > > > > > > > >> > > > > > > all the taskmanagers whether the latest
> rules
> > of
> > > > the
> > > > > > > > > >> taskmanager is
> > > > > > > > > >> > > > > equal
> > > > > > > > > >> > > > > > > to these of the Operator Coordinator.
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > Just to be sure, this indeed would mean that
> > if
> > > > for
> > > > > > > > whatever
> > > > > > > > > >> reason
> > > > > > > > > >> > > > the
> > > > > > > > > >> > > > > > > heartbeat timeout, it would crash the job,
> > > right?
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > -- We have consided about the solution
> > mentioned
> > > > > > above.
> > > > > > > In
> > > > > > > > > >> this
> > > > > > > > > >> > > > > > solution, I
> > > > > > > > > >> > > > > > > have some questions about how to guarantee
> the
> > > > > > > consistency
> > > > > > > > > of
> > > > > > > > > >> the
> > > > > > > > > >> > > > rule
> > > > > > > > > >> > > > > > > between each TaskManager. By having a
> > coodinator
> > > > in
> > > > > > the
> > > > > > > > > >> JobManager
> > > > > > > > > >> > > to
> > > > > > > > > >> > > > > > > centrally manage the latest rules, the
> latest
> > > > rules
> > > > > of
> > > > > > > all
> > > > > > > > > >> > > > TaskManagers
> > > > > > > > > >> > > > > > are
> > > > > > > > > >> > > > > > > consistent with those of the JobManager, so
> as
> > > to
> > > > > > avoid
> > > > > > > > the
> > > > > > > > > >> > > > > > inconsistencies
> > > > > > > > > >> > > > > > > that may be encountered in the above
> solution.
> > > Can
> > > > > you
> > > > > > > > > >> introduce
> > > > > > > > > >> > > how
> > > > > > > > > >> > > > > this
> > > > > > > > > >> > > > > > > solution guarantees the consistency of the
> > > rules?
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > The consistency that we could guarantee was
> > > based
> > > > on
> > > > > > how
> > > > > > > > > >> often each
> > > > > > > > > >> > > > > > > TaskManager would do a refresh and how often
> > we
> > > > > would
> > > > > > > > > accept a
> > > > > > > > > >> > > > refresh
> > > > > > > > > >> > > > > to
> > > > > > > > > >> > > > > > > fail. We set the refresh time to a
> relatively
> > > > short
> > > > > > one
> > > > > > > > (30
> > > > > > > > > >> > > seconds)
> > > > > > > > > >> > > > > and
> > > > > > > > > >> > > > > > > maximum failures to 3. That meant that we
> > could
> > > > > > > guarantee
> > > > > > > > > that
> > > > > > > > > >> > > rules
> > > > > > > > > >> > > > > > would
> > > > > > > > > >> > > > > > > be updated in < 2 minutes or else the job
> > would
> > > > > crash.
> > > > > > > > That
> > > > > > > > > >> was
> > > > > > > > > >> > > > > > sufficient
> > > > > > > > > >> > > > > > > for our use cases. This also really depends
> on
> > > how
> > > > > big
> > > > > > > > your
> > > > > > > > > >> cluster
> > > > > > > > > >> > > > > is. I
> > > > > > > > > >> > > > > > > can imagine that if you have a large scale
> > > cluster
> > > > > > that
> > > > > > > > you
> > > > > > > > > >> want to
> > > > > > > > > >> > > > > run,
> > > > > > > > > >> > > > > > > you don't want to DDOS the backend system
> > where
> > > > you
> > > > > > have
> > > > > > > > > your
> > > > > > > > > >> rules
> > > > > > > > > >> > > > > > stored.
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > -- In summary, the current design is that
> > > > JobManager
> > > > > > > tells
> > > > > > > > > all
> > > > > > > > > >> > > > > > TaskManagers
> > > > > > > > > >> > > > > > > the latest rules through OperatorCoodinator,
> > and
> > > > > will
> > > > > > > > > >> initiate a
> > > > > > > > > >> > > > > > heartbeat
> > > > > > > > > >> > > > > > > to check whether the latest rules on each
> > > > > TaskManager
> > > > > > > are
> > > > > > > > > >> > > consistent.
> > > > > > > > > >> > > > > We
> > > > > > > > > >> > > > > > > will describe how to deal with the Failover
> > > > scenario
> > > > > > in
> > > > > > > > more
> > > > > > > > > >> detail
> > > > > > > > > >> > > > on
> > > > > > > > > >> > > > > > FLIP.
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > Thanks for that. I think having the
> JobManager
> > > > tell
> > > > > > the
> > > > > > > > > >> > > TaskManagers
> > > > > > > > > >> > > > > the
> > > > > > > > > >> > > > > > > applicable rules would indeed end up being
> the
> > > > best
> > > > > > > > design.
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > -- about the concerns around consistency
> > raised
> > > by
> > > > > > > > Martijn:
> > > > > > > > > I
> > > > > > > > > >> > > think a
> > > > > > > > > >> > > > > lot
> > > > > > > > > >> > > > > > > of those can be mitigated by using an event
> > time
> > > > > > > timestamp
> > > > > > > > > >> from
> > > > > > > > > >> > > which
> > > > > > > > > >> > > > > the
> > > > > > > > > >> > > > > > > rules take effect. The reprocessing
> scenario,
> > > for
> > > > > > > example,
> > > > > > > > > is
> > > > > > > > > >> > > covered
> > > > > > > > > >> > > > > by
> > > > > > > > > >> > > > > > > this. If a pattern processor should become
> > > active
> > > > as
> > > > > > > soon
> > > > > > > > as
> > > > > > > > > >> > > > possible,
> > > > > > > > > >> > > > > > > there will still be inconsistencies between
> > > > > > > Taskmanagers,
> > > > > > > > > but
> > > > > > > > > >> "as
> > > > > > > > > >> > > > soon
> > > > > > > > > >> > > > > as
> > > > > > > > > >> > > > > > > possible" is vague anyway, which is why I
> > think
> > > > > that's
> > > > > > > ok.
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > I think an event timestamp is indeed a
> really
> > > > > > important
> > > > > > > > one.
> > > > > > > > > >> We
> > > > > > > > > >> > > also
> > > > > > > > > >> > > > > used
> > > > > > > > > >> > > > > > > that in my previous role, with the
> > > > > > > ruleActivationTimestamp
> > > > > > > > > >> compared
> > > > > > > > > >> > > > to
> > > > > > > > > >> > > > > > > eventtime (well, actually we used Kafka
> > > logAppend
> > > > > time
> > > > > > > > > because
> > > > > > > > > >> > > > > > > eventtime wasn't always properly set so we
> > used
> > > > that
> > > > > > > time
> > > > > > > > to
> > > > > > > > > >> > > > overwrite
> > > > > > > > > >> > > > > > the
> > > > > > > > > >> > > > > > > eventtime from the event itself).
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > Best regards,
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > Martijn
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin
> > Knauf <
> > > > > > > > > >> knaufk@apache.org>
> > > > > > > > > >> > > > > > wrote:
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > about the concerns around consistency
> raised
> > > by
> > > > > > > > Martijn: I
> > > > > > > > > >> think
> > > > > > > > > >> > > a
> > > > > > > > > >> > > > > lot
> > > > > > > > > >> > > > > > of
> > > > > > > > > >> > > > > > > > those can be mitigated by using an event
> > time
> > > > > > > timestamp
> > > > > > > > > from
> > > > > > > > > >> > > which
> > > > > > > > > >> > > > > the
> > > > > > > > > >> > > > > > > > rules take effect. The reprocessing
> > scenario,
> > > > for
> > > > > > > > example,
> > > > > > > > > >> is
> > > > > > > > > >> > > > covered
> > > > > > > > > >> > > > > > by
> > > > > > > > > >> > > > > > > > this. If a pattern processor should become
> > > > active
> > > > > as
> > > > > > > > soon
> > > > > > > > > as
> > > > > > > > > >> > > > > possible,
> > > > > > > > > >> > > > > > > > there will still be inconsistencies
> between
> > > > > > > > Taskmanagers,
> > > > > > > > > >> but "as
> > > > > > > > > >> > > > > soon
> > > > > > > > > >> > > > > > as
> > > > > > > > > >> > > > > > > > possible" is vague anyway, which is why I
> > > think
> > > > > > that's
> > > > > > > > ok.
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > about naming: The naming with
> > > "PatternProcessor"
> > > > > > > sounds
> > > > > > > > > >> good to
> > > > > > > > > >> > > me.
> > > > > > > > > >> > > > > > Final
> > > > > > > > > >> > > > > > > > nit: I would go for
> CEP#patternProccessors,
> > > > which
> > > > > > > would
> > > > > > > > be
> > > > > > > > > >> > > > consistent
> > > > > > > > > >> > > > > > with
> > > > > > > > > >> > > > > > > > CEP#pattern.
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > I am not sure about one of the rejected
> > > > > > alternatives:
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > > Have each subtask of an operator make
> the
> > > > update
> > > > > > on
> > > > > > > > > their
> > > > > > > > > >> own
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > -
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > It is hard to achieve consistency.
> > > > > > > > > >> > > > > > > > -
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > Though the time interval that each
> > > subtask
> > > > > > makes
> > > > > > > > the
> > > > > > > > > >> update
> > > > > > > > > >> > > > can
> > > > > > > > > >> > > > > > be
> > > > > > > > > >> > > > > > > > the same, the absolute time they
> make
> > > the
> > > > > > update
> > > > > > > > > >> might be
> > > > > > > > > >> > > > > > different.
> > > > > > > > > >> > > > > > > > For
> > > > > > > > > >> > > > > > > > example, one makes updates at 10:00,
> > > > 10:05,
> > > > > > etc,
> > > > > > > > > while
> > > > > > > > > >> > > > another
> > > > > > > > > >> > > > > > does
> > > > > > > > > >> > > > > > > > it at
> > > > > > > > > >> > > > > > > > 10:01, 10:06. In this case the
> > subtasks
> > > > > might
> > > > > > > > never
> > > > > > > > > >> > > > processing
> > > > > > > > > >> > > > > > data
> > > > > > > > > >> > > > > > > > with
> > > > > > > > > >> > > > > > > > the same set of pattern processors.
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > I would have thought that it is quite easy
> > to
> > > > poll
> > > > > > for
> > > > > > > > the
> > > > > > > > > >> rules
> > > > > > > > > >> > > > from
> > > > > > > > > >> > > > > > each
> > > > > > > > > >> > > > > > > > Subtask at *about *the same time. So, this
> > > alone
> > > > > > does
> > > > > > > > not
> > > > > > > > > >> seem to
> > > > > > > > > >> > > > be
> > > > > > > > > >> > > > > > > > enough to rule out this option. I've
> looped
> > in
> > > > > David
> > > > > > > > > >> Moravek to
> > > > > > > > > >> > > get
> > > > > > > > > >> > > > > his
> > > > > > > > > >> > > > > > > > opinion of the additional load imposed on
> > the
> > > > JM.
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > Thanks,
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > Konstantin
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas
> > > Jiang <
> > > > > > > > > >> > > > > > nicholasjiang@apache.org>
> > > > > > > > > >> > > > > > > > wrote:
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > > Hi Yue,
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > Thanks for your feedback of the FLIP. I
> > have
> > > > > > > addressed
> > > > > > > > > >> your
> > > > > > > > > >> > > > > > questions and
> > > > > > > > > >> > > > > > > > > made a corresponding explanation as
> > follows:
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > > > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > > > > >> > > > to
> > > > > > > > > >> > > > > > > > update
> > > > > > > > > >> > > > > > > > > the rules, will it increase the load of
> > JM?
> > > > For
> > > > > > > > example,
> > > > > > > > > >> if the
> > > > > > > > > >> > > > > user
> > > > > > > > > >> > > > > > > > wants
> > > > > > > > > >> > > > > > > > > the updated rule to take effect
> > > immediately,,
> > > > > > which
> > > > > > > > > means
> > > > > > > > > >> that
> > > > > > > > > >> > > we
> > > > > > > > > >> > > > > > need to
> > > > > > > > > >> > > > > > > > > set a shorter check interval or there is
> > > > another
> > > > > > > > > scenario
> > > > > > > > > >> when
> > > > > > > > > >> > > > > users
> > > > > > > > > >> > > > > > > > rarely
> > > > > > > > > >> > > > > > > > > update the pattern, will the
> > > > > > > > PatternProcessoerDiscoverer
> > > > > > > > > >> be in
> > > > > > > > > >> > > > most
> > > > > > > > > >> > > > > > of
> > > > > > > > > >> > > > > > > > the
> > > > > > > > > >> > > > > > > > > time Do useless checks ? Will a lazy
> > update
> > > > mode
> > > > > > > could
> > > > > > > > > be
> > > > > > > > > >> used,
> > > > > > > > > >> > > > > > which the
> > > > > > > > > >> > > > > > > > > pattern only be updated when triggered
> by
> > > the
> > > > > > user,
> > > > > > > > and
> > > > > > > > > do
> > > > > > > > > >> > > > nothing
> > > > > > > > > >> > > > > at
> > > > > > > > > >> > > > > > > > other
> > > > > > > > > >> > > > > > > > > times?
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > PatternProcessoerDiscoverer is a
> > > user-defined
> > > > > > > > interface
> > > > > > > > > to
> > > > > > > > > >> > > > discover
> > > > > > > > > >> > > > > > the
> > > > > > > > > >> > > > > > > > > PatternProcessor updates. Periodically
> > > > checking
> > > > > > the
> > > > > > > > > >> > > > > PatternProcessor
> > > > > > > > > >> > > > > > in
> > > > > > > > > >> > > > > > > > the
> > > > > > > > > >> > > > > > > > > database is a implementation of the
> > > > > > > > > >> PatternProcessoerDiscoverer
> > > > > > > > > >> > > > > > > > interface,
> > > > > > > > > >> > > > > > > > > which is that periodically querys all
> the
> > > > > > > > > PatternProcessor
> > > > > > > > > >> > > table
> > > > > > > > > >> > > > in
> > > > > > > > > >> > > > > > > > certain
> > > > > > > > > >> > > > > > > > > interval. This implementation indeeds
> has
> > > the
> > > > > > > useless
> > > > > > > > > >> checks,
> > > > > > > > > >> > > and
> > > > > > > > > >> > > > > > could
> > > > > > > > > >> > > > > > > > > directly integrates the changelog of the
> > > > table.
> > > > > In
> > > > > > > > > >> addition, in
> > > > > > > > > >> > > > > > addition
> > > > > > > > > >> > > > > > > > to
> > > > > > > > > >> > > > > > > > > the implementation of periodically
> > checking
> > > > the
> > > > > > > > > database,
> > > > > > > > > >> there
> > > > > > > > > >> > > > are
> > > > > > > > > >> > > > > > other
> > > > > > > > > >> > > > > > > > > implementations such as the
> > PatternProcessor
> > > > > that
> > > > > > > > > provides
> > > > > > > > > >> > > > Restful
> > > > > > > > > >> > > > > > > > services
> > > > > > > > > >> > > > > > > > > to receive updates.
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > -- I still have some confusion about
> how
> > > Key
> > > > > > > > Generating
> > > > > > > > > >> > > > Opertator
> > > > > > > > > >> > > > > > and
> > > > > > > > > >> > > > > > > > > CepOperator (Pattern Matching &
> Processing
> > > > > > Operator)
> > > > > > > > > work
> > > > > > > > > >> > > > together.
> > > > > > > > > >> > > > > > If
> > > > > > > > > >> > > > > > > > > there are N PatternProcessors, will the
> > Key
> > > > > > > Generating
> > > > > > > > > >> > > Opertator
> > > > > > > > > >> > > > > > > > generate N
> > > > > > > > > >> > > > > > > > > keyedStreams, and then N CepOperator
> would
> > > > > process
> > > > > > > > each
> > > > > > > > > >> Key
> > > > > > > > > >> > > > > > separately ?
> > > > > > > > > >> > > > > > > > Or
> > > > > > > > > >> > > > > > > > > every CepOperator Task would process all
> > > > > patterns,
> > > > > > > if
> > > > > > > > > so,
> > > > > > > > > >> does
> > > > > > > > > >> > > > the
> > > > > > > > > >> > > > > > key
> > > > > > > > > >> > > > > > > > type
> > > > > > > > > >> > > > > > > > > in each PatternProcessor need to be the
> > > same?
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > Firstly the Pattern Matching &
> Processing
> > > > > Operator
> > > > > > > is
> > > > > > > > > not
> > > > > > > > > >> the
> > > > > > > > > >> > > > > > CepOperator
> > > > > > > > > >> > > > > > > > > at present, because CepOperator
> mechanism
> > is
> > > > > based
> > > > > > > on
> > > > > > > > > the
> > > > > > > > > >> > > > NFAState.
> > > > > > > > > >> > > > > > > > > Secondly if there are N
> PatternProcessors,
> > > the
> > > > > Key
> > > > > > > > > >> Generating
> > > > > > > > > >> > > > > > Opertator
> > > > > > > > > >> > > > > > > > > combines all the keyedStreams with
> keyBy()
> > > > > > > operation,
> > > > > > > > > >> thus the
> > > > > > > > > >> > > > > > Pattern
> > > > > > > > > >> > > > > > > > > Matching & Processing Operator would
> > process
> > > > all
> > > > > > the
> > > > > > > > > >> patterns.
> > > > > > > > > >> > > In
> > > > > > > > > >> > > > > > other
> > > > > > > > > >> > > > > > > > > words, the KeySelector of the
> > > PatternProcessor
> > > > > is
> > > > > > > used
> > > > > > > > > >> for the
> > > > > > > > > >> > > > Key
> > > > > > > > > >> > > > > > > > > Generating Opertator, and the Pattern
> and
> > > > > > > > > >> > > PatternProceessFunction
> > > > > > > > > >> > > > > of
> > > > > > > > > >> > > > > > the
> > > > > > > > > >> > > > > > > > > PatternProcessor are used for the
> Pattern
> > > > > > Matching &
> > > > > > > > > >> Processing
> > > > > > > > > >> > > > > > Operator.
> > > > > > > > > >> > > > > > > > > Lastly the key type in each
> > PatternProcessor
> > > > is
> > > > > > the
> > > > > > > > > same,
> > > > > > > > > >> > > > regarded
> > > > > > > > > >> > > > > as
> > > > > > > > > >> > > > > > > > > Object type.
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > -- Maybe need to pay attention to it
> when
> > > > > > > implementing
> > > > > > > > > it
> > > > > > > > > >> .If
> > > > > > > > > >> > > > some
> > > > > > > > > >> > > > > > > > Pattern
> > > > > > > > > >> > > > > > > > > has been removed or updated, will the
> > > > partially
> > > > > > > > matched
> > > > > > > > > >> results
> > > > > > > > > >> > > > in
> > > > > > > > > >> > > > > > > > > StateBackend would be clean up or We
> rely
> > on
> > > > > state
> > > > > > > ttl
> > > > > > > > > to
> > > > > > > > > >> clean
> > > > > > > > > >> > > > up
> > > > > > > > > >> > > > > > these
> > > > > > > > > >> > > > > > > > > expired states.
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > If certain Pattern has been removed or
> > > > updated,
> > > > > > the
> > > > > > > > > >> partially
> > > > > > > > > >> > > > > matched
> > > > > > > > > >> > > > > > > > > results in StateBackend would be clean
> up
> > > > until
> > > > > > the
> > > > > > > > next
> > > > > > > > > >> > > > > checkpoint.
> > > > > > > > > >> > > > > > The
> > > > > > > > > >> > > > > > > > > partially matched result doesn't depend
> on
> > > the
> > > > > > state
> > > > > > > > ttl
> > > > > > > > > >> of the
> > > > > > > > > >> > > > > > > > > StateBackend.
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > 4. Will the PatternProcessorManager keep
> > all
> > > > the
> > > > > > > > active
> > > > > > > > > >> > > > > > PatternProcessor
> > > > > > > > > >> > > > > > > > > in memory? We have also Support Multiple
> > > Rule
> > > > > and
> > > > > > > > > Dynamic
> > > > > > > > > >> Rule
> > > > > > > > > >> > > > > > Changing.
> > > > > > > > > >> > > > > > > > > But we are facing such a problem, some
> > > users’
> > > > > > usage
> > > > > > > > > >> scenarios
> > > > > > > > > >> > > are
> > > > > > > > > >> > > > > > that
> > > > > > > > > >> > > > > > > > they
> > > > > > > > > >> > > > > > > > > want to have their own pattern for each
> > > > user_id,
> > > > > > > which
> > > > > > > > > >> means
> > > > > > > > > >> > > that
> > > > > > > > > >> > > > > > there
> > > > > > > > > >> > > > > > > > > could be thousands of patterns, which
> > would
> > > > make
> > > > > > the
> > > > > > > > > >> > > performance
> > > > > > > > > >> > > > of
> > > > > > > > > >> > > > > > > > Pattern
> > > > > > > > > >> > > > > > > > > Matching very poor. We are also trying
> to
> > > > solve
> > > > > > this
> > > > > > > > > >> problem.
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > The PatternProcessorManager keeps all
> the
> > > > active
> > > > > > > > > >> > > PatternProcessor
> > > > > > > > > >> > > > > in
> > > > > > > > > >> > > > > > > > > memory. For scenarios that they want to
> > have
> > > > > their
> > > > > > > own
> > > > > > > > > >> pattern
> > > > > > > > > >> > > > for
> > > > > > > > > >> > > > > > each
> > > > > > > > > >> > > > > > > > > user_id, IMO, is it possible to reduce
> the
> > > > > > > > fine-grained
> > > > > > > > > >> pattern
> > > > > > > > > >> > > > of
> > > > > > > > > >> > > > > > > > > PatternProcessor to solve the
> performance
> > > > > problem
> > > > > > of
> > > > > > > > the
> > > > > > > > > >> > > Pattern
> > > > > > > > > >> > > > > > > > Matching,
> > > > > > > > > >> > > > > > > > > for example, a pattern corresponds to a
> > > group
> > > > of
> > > > > > > > users?
> > > > > > > > > >> The
> > > > > > > > > >> > > > > scenarios
> > > > > > > > > >> > > > > > > > > mentioned above need to be solved by
> case
> > by
> > > > > case.
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > Best,
> > > > > > > > > >> > > > > > > > > Nicholas Jiang
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > > > > > > > >> > > > > > > > > > Glad to see the Community's progress
> in
> > > > Flink
> > > > > > CEP.
> > > > > > > > > After
> > > > > > > > > >> > > > reading
> > > > > > > > > >> > > > > > this
> > > > > > > > > >> > > > > > > > > Flip,
> > > > > > > > > >> > > > > > > > > > I have few questions, would you please
> > > take
> > > > a
> > > > > > look
> > > > > > > > ?
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > > > > > > > >> > > > PatternProcessoerDiscoverer
> > > > > > > > > >> > > > > to
> > > > > > > > > >> > > > > > > > > update
> > > > > > > > > >> > > > > > > > > > the rules, will it increase the load
> of
> > > JM?
> > > > > For
> > > > > > > > > >> example, if
> > > > > > > > > >> > > the
> > > > > > > > > >> > > > > > user
> > > > > > > > > >> > > > > > > > > wants
> > > > > > > > > >> > > > > > > > > > the updated rule to take effect
> > > > immediately,,
> > > > > > > which
> > > > > > > > > >> means
> > > > > > > > > >> > > that
> > > > > > > > > >> > > > we
> > > > > > > > > >> > > > > > need
> > > > > > > > > >> > > > > > > > to
> > > > > > > > > >> > > > > > > > > > set a shorter check interval or there
> > is
> > > > > > another
> > > > > > > > > >> scenario
> > > > > > > > > >> > > when
> > > > > > > > > >> > > > > > users
> > > > > > > > > >> > > > > > > > > > rarely update the pattern, will the
> > > > > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > > > > >> > > > > be
> > > > > > > > > >> > > > > > in
> > > > > > > > > >> > > > > > > > > most
> > > > > > > > > >> > > > > > > > > > of the time Do useless checks ? Will a
> > > lazy
> > > > > > update
> > > > > > > > > mode
> > > > > > > > > >> could
> > > > > > > > > >> > > > be
> > > > > > > > > >> > > > > > used,
> > > > > > > > > >> > > > > > > > > > which the pattern only be updated when
> > > > > triggered
> > > > > > > by
> > > > > > > > > the
> > > > > > > > > >> user,
> > > > > > > > > >> > > > and
> > > > > > > > > >> > > > > > do
> > > > > > > > > >> > > > > > > > > > nothing at other times ?
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > 2. I still have some confusion about
> > how
> > > > Key
> > > > > > > > > >> Generating
> > > > > > > > > >> > > > > > Opertator and
> > > > > > > > > >> > > > > > > > > > CepOperator (Pattern Matching &
> > Processing
> > > > > > > Operator)
> > > > > > > > > >> work
> > > > > > > > > >> > > > > > together. If
> > > > > > > > > >> > > > > > > > > > there are N PatternProcessors, will
> the
> > > Key
> > > > > > > > Generating
> > > > > > > > > >> > > > Opertator
> > > > > > > > > >> > > > > > > > > generate N
> > > > > > > > > >> > > > > > > > > > keyedStreams, and then N CepOperator
> > would
> > > > > > process
> > > > > > > > > each
> > > > > > > > > >> Key
> > > > > > > > > >> > > > > > separately
> > > > > > > > > >> > > > > > > > ?
> > > > > > > > > >> > > > > > > > > Or
> > > > > > > > > >> > > > > > > > > > every CepOperator Task would process
> all
> > > > > > patterns,
> > > > > > > > if
> > > > > > > > > >> so,
> > > > > > > > > >> > > does
> > > > > > > > > >> > > > > the
> > > > > > > > > >> > > > > > key
> > > > > > > > > >> > > > > > > > > type
> > > > > > > > > >> > > > > > > > > > in each PatternProcessor need to be
> the
> > > > same ?
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > 3. Maybe need to pay attention to it
> > when
> > > > > > > > implementing
> > > > > > > > > >> it .If
> > > > > > > > > >> > > > > some
> > > > > > > > > >> > > > > > > > > Pattern
> > > > > > > > > >> > > > > > > > > > has been removed or updateed ,will
> the
> > > > > > partially
> > > > > > > > > >> matched
> > > > > > > > > >> > > > results
> > > > > > > > > >> > > > > > in
> > > > > > > > > >> > > > > > > > > > StateBackend would be clean up or We
> > rely
> > > on
> > > > > > state
> > > > > > > > ttl
> > > > > > > > > >> to
> > > > > > > > > >> > > clean
> > > > > > > > > >> > > > > up
> > > > > > > > > >> > > > > > > > these
> > > > > > > > > >> > > > > > > > > > expired states.
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > 4. Will the PatternProcessorManager
> keep
> > > all
> > > > > the
> > > > > > > > > active
> > > > > > > > > >> > > > > > > > PatternProcessor
> > > > > > > > > >> > > > > > > > > in
> > > > > > > > > >> > > > > > > > > > memory ? We have also Support Multiple
> > > Rule
> > > > > and
> > > > > > > > > Dynamic
> > > > > > > > > >> Rule
> > > > > > > > > >> > > > > > Changing .
> > > > > > > > > >> > > > > > > > > > But we are facing such a problem, some
> > > > users’
> > > > > > > usage
> > > > > > > > > >> scenarios
> > > > > > > > > >> > > > are
> > > > > > > > > >> > > > > > that
> > > > > > > > > >> > > > > > > > > they
> > > > > > > > > >> > > > > > > > > > want to have their own pattern for
> each
> > > > > user_id,
> > > > > > > > which
> > > > > > > > > >> means
> > > > > > > > > >> > > > that
> > > > > > > > > >> > > > > > there
> > > > > > > > > >> > > > > > > > > > could be thousands of patterns, which
> > > would
> > > > > make
> > > > > > > the
> > > > > > > > > >> > > > performance
> > > > > > > > > >> > > > > of
> > > > > > > > > >> > > > > > > > > Pattern
> > > > > > > > > >> > > > > > > > > > Matching very poor. We are also trying
> > to
> > > > > solve
> > > > > > > this
> > > > > > > > > >> problem.
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > Yunfeng Zhou <
> > flink.zhouyunfeng@gmail.com
> > > >
> > > > > > > > > >> 于2021年12月10日周五
> > > > > > > > > >> > > > > 19:16写道：
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > Hi all，
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > I'm opening this thread to propose
> the
> > > > > design
> > > > > > to
> > > > > > > > > >> support
> > > > > > > > > >> > > > > multiple
> > > > > > > > > >> > > > > > > > rule
> > > > > > > > > >> > > > > > > > > &
> > > > > > > > > >> > > > > > > > > > > dynamic rule changing in the
> Flink-CEP
> > > > > > project,
> > > > > > > as
> > > > > > > > > >> > > described
> > > > > > > > > >> > > > in
> > > > > > > > > >> > > > > > > > > FLIP-200
> > > > > > > > > >> > > > > > > > > > > [1]
> > > > > > > > > >> > > > > > > > > > > .
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > Currently Flink CEP only supports
> > > having a
> > > > > > > single
> > > > > > > > > >> pattern
> > > > > > > > > >> > > > > inside
> > > > > > > > > >> > > > > > a
> > > > > > > > > >> > > > > > > > > > > CepOperator and does not support
> > > changing
> > > > > the
> > > > > > > > > pattern
> > > > > > > > > >> > > > > > dynamically. In
> > > > > > > > > >> > > > > > > > > order
> > > > > > > > > >> > > > > > > > > > > to reduce resource consumption and
> to
> > > > > > experience
> > > > > > > > > >> shorter
> > > > > > > > > >> > > > > downtime
> > > > > > > > > >> > > > > > > > > during
> > > > > > > > > >> > > > > > > > > > > pattern updates, there is a growing
> > need
> > > > in
> > > > > > the
> > > > > > > > > >> production
> > > > > > > > > >> > > > > > > > environment
> > > > > > > > > >> > > > > > > > > that
> > > > > > > > > >> > > > > > > > > > > expects CEP to support having
> multiple
> > > > > > patterns
> > > > > > > in
> > > > > > > > > one
> > > > > > > > > >> > > > operator
> > > > > > > > > >> > > > > > and
> > > > > > > > > >> > > > > > > > to
> > > > > > > > > >> > > > > > > > > > > support dynamically changing them.
> > > > > Therefore I
> > > > > > > > > >> propose to
> > > > > > > > > >> > > add
> > > > > > > > > >> > > > > > certain
> > > > > > > > > >> > > > > > > > > > > infrastructure as described in
> > FLIP-200
> > > to
> > > > > > > support
> > > > > > > > > >> these
> > > > > > > > > >> > > > > > > > > functionalities.
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > Please feel free to reply to this
> > email
> > > > > > thread.
> > > > > > > > > >> Looking
> > > > > > > > > >> > > > forward
> > > > > > > > > >> > > > > > to
> > > > > > > > > >> > > > > > > > your
> > > > > > > > > >> > > > > > > > > > > feedback!
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > [1]
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > >
> > > > > > > > > >> > >
> > > > > > > > > >>
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > Best regards,
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > > > Yunfeng
> > > > > > > > > >> > > > > > > > > > >
> > > > > > > > > >> > > > > > > > > >
> > > > > > > > > >> > > > > > > > >
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > --
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > Konstantin Knauf
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > https://twitter.com/snntrable
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > > > https://github.com/knaufk
> > > > > > > > > >> > > > > > > >
> > > > > > > > > >> > > > > > >
> > > > > > > > > >> > > > > >
> > > > > > > > > >> > > > >
> > > > > > > > > >> > > >
> > > > > > > > > >> > >
> > > > > > > > > >> > >
> > > > > > > > > >> > > --
> > > > > > > > > >> > >
> > > > > > > > > >> > > Konstantin Knauf
> > > > > > > > > >> > >
> > > > > > > > > >> > > https://twitter.com/snntrable
> > > > > > > > > >> > >
> > > > > > > > > >> > > https://github.com/knaufk
> > > > > > > > > >> > >
> > > > > > > > > >> >
> > > > > > > > > >>
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Till Rohrmann <tr...@apache.org>.
Hi Becket,
I might be missing something but having to define interfaces/formats for
the CEP patterns should be necessary for either approach. The OC approach
needs to receive and understand the pattern data from somewhere as well and
will probably also have to deal with evolving formats. Hence, I believe
that this work wouldn't be wasted.
I might misjudge the willingness of our users to do some extra set up work,
but I think that some of them would already be happy with state 1.
My understanding so far was that the OC approach also requires the CEP
operator infrastructure (making the operator accept new patterns) work that
I proposed to do as a first step. The only difference is where the new
patterns/commands are coming from. If we design this correctly, then this
should change only very little depending on whether you read from a
side-input or from an OC.
Another benefit of downscoping the FLIP is to make it more realistic to be
completed. Smaller and incremental steps are usually easier to realize. If
we now say that this FLIP requires a general purpose user controlled
control plane that gives you hard guarantees, then I am pretty sure that
this will take at least half a year.
Cheers,
Till
On Thu, Jan 6, 2022 at 4:45 AM Becket Qin <be...@gmail.com> wrote:
> Thanks for the explanation, Till. I like the idea, but have a question
> about the first step.
>
> After the first step, would users be able to actually use the dynamic
> patterns in CEP?
>
> In the first step you mentioned, the commands and formats for a new CEP
> pattern seem related to how users would ingest the commands. If we go with
> the OC, these commands and formats would become internal interfaces. The
> end users would just use the REST API, or in the beginning, implement a
> Java plugin of dynamic pattern provider. In this case our focus would be on
> designing a good plugin interface. On the other hand, if we go with the
> side-input, users would need to know the command format so they can send
> the commands to the CEP operator. Therefore we need to think about stuff
> like versioning, request validation and backwards compatibility.
>
> Also, because the public interface is all about how the users can ingest
> the dynamic patterns. It seems we still need to figure that out before we
> can conclude the FLIP.
>
> Assuming the first step closes this FLIP and after that users would be able
> to use the CEP dynamic pattern, are you suggesting the following?
>
> 1. We will design the commands and format of CEP dynamic pattern, and also
> how CEP operators take them into effect. This design would assume that
> users can send the commands directly to the CEP operator via side-input. So
> the protocol would take versioning and format evolution into account. After
> the first step, the users CAN make dynamic pattern work with the help from
> some external dependencies and maintenance effort.
>
> 2. Discuss about a control plane from the use case of CEP dynamic pattern,
> and let CEP dynamic pattern use that control plane if we eventually think
> that is the right way to go.
>
> Assuming that we are not going to stop after step 1 is done, will the end
> state be that the CEP dynamic pattern supports both approaches? It is not
> clear to me how this would work. For example, will a pattern ingested from
> side-input be managed by OC as well? If more and more users pick the more
> ergonomic way, would the side-input option just die out? In that case, will
> we deprecate that?
>
> My main concern is that the time and work we invest in step 1 will be
> thrown away. Not only that, at the end of step 1, in order to actually use
> the feature and make it production ready, there is a lot of work for the
> users to do. All that work may also become in vain. So it would be good if
> we can avoid that by having a clean approach to begin with. What do you
> think?
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
>
> On Wed, Jan 5, 2022 at 11:35 PM Till Rohrmann <tr...@apache.org>
> wrote:
>
> > I think I would scope the effort slightly differently. Note that I might
> be
> > missing some requirements or overlook something.
> >
> > 1. Enable Flink to support CEP dynamic patterns
> >
> > Here I would define the commands and formats for a new CEP pattern. Then
> I
> > would extend the CEP operator to understand these commands so that we can
> > change the CEP patterns dynamically. This should give the building blocks
> > to set up a job where you can change the CEP patterns by reading from an
> > arbitrary side input the CEP pattern commands. Note that it will be the
> > responsibility of the user to ingest the data somehow. This is nothing
> > Flink is concerned with at this time.
> >
> > 2. Think about how to make the CEP dynamic pattern feature more ergonomic
> >
> > Here we can pick up the discussion about OC and having a REST ingestion
> > endpoint in Flink vs. offering tools that live outside of Flink itself. I
> > could imagine that this could become a separate small project that builds
> > upon Flink, for example.
> >
> > Cheers,
> > Till
> >
> > On Wed, Jan 5, 2022 at 2:19 PM Becket Qin <be...@gmail.com> wrote:
> >
> > > Hi Till,
> > >
> > > Thanks for the prompt reply. Like you said, we are indeed using the
> > dynamic
> > > CEP pattern use case to test the existing primitives in Flink to see if
> > > they can meet the requirements. I fully understand the concern of
> > > exposing OC as a user interface. Meanwhile I see CEP dynamic patterns
> as
> > a
> > > good opportunity to battle test and enhance the OC as a user facing
> > control
> > > plane which is currently missing. After all, there is no better person
> > than
> > > ourselves to try it out first.
> > >
> > > It is not clear to me whether it is worth continuing the effort of
> > > supporting dynamic CEP pattern without concluding the control plane
> > > discussion. Let's say we have a CEP job reading from Kafka. To make
> this
> > > work with side-input, a few things need to be done.
> > >
> > > 1. In order to support dynamic patterns, users would create another
> > > Kafka topic as side-input to receive dynamic patterns.
> > > 2. In order to insert dynamic patterns, users would use a separate
> web
> > > server that is provided by us as a separate tool. The web server
> takes
> > > http
> > > requests and sends dynamic pattern records to Kafka via a Kafka sink
> > > (using
> > > a KafkaProducer is likely simpler here, though).
> > > 3. Regarding querying the running dynamic patterns, given Kafka is
> not
> > > queryable, users would probably introduce a database and insert the
> > > patterns there so they can query the running patterns. Maybe this
> > could
> > > be
> > > done by the CEP operator side-output, so there is less chance of
> > > inconsistency between Kafka and the database.
> > > 4. If the Flink job is to be stopped, the dynamic pattern Kafka
> topic
> > > needs to be deleted, the companion web server also needs to be
> stopped
> > > (assuming it is not shared with other CEP jobs), and the database
> > table
> > > storing the dynamic pattern needs to be dropped.
> > >
> > > Please correct me if I misunderstood something, but this seems quite
> > > involved. Moreover, all the work here is going to be thrown away after
> we
> > > have OC as a decent user facing control plane in place. And we will
> > likely
> > > have a backwards incompatible API change here. Given that, I am
> wondering
> > > if we should wait until the OC discussion concludes before moving on
> with
> > > the dynamic patterns?
> > >
> > > Thanks,
> > >
> > > Jiangjie (Becket) Qin
> > >
> > >
> > >
> > > On Wed, Jan 5, 2022 at 5:53 PM Till Rohrmann <tr...@apache.org>
> > wrote:
> > >
> > > > Thanks for the detailed explanation Becket.
> > > >
> > > > Do you think that an additional dependency is a deal breaker for
> people
> > > to
> > > > use dynamic CEP patterns? At the very least people have to operate
> some
> > > > kind of storage/queue system from which the CEP job can read anyway.
> > > Maybe
> > > > it could be good enough to provide a REST endpoint (as a separate
> tool)
> > > > that can be instantiated with a Flink sink to ingest REST requests
> > > > into some queue. A general concern I have is that by making the JM a
> > REST
> > > > ingestion point for data will push another responsibility to Flink
> and
> > > > increase the surface area further.
> > > >
> > > > For how to handle data that cannot be processed by patterns, I think
> > > there
> > > > also exist other solutions. I could imagine that users could define
> > > > different failover strategies. E.g. one could simply ignore the
> record,
> > > the
> > > > pattern could get deactivated on the affected TM or the processing
> > fails.
> > > >
> > > > Maybe we are coupling the dynamic CEP pattern effort too much on
> where
> > > the
> > > > new patterns come from. Maybe we can split these efforts into
> > supporting
> > > > dynamic CEP patterns on the TM reading from some source and then fork
> > off
> > > > the discussion about introducing a user controlled control plane to
> > > Flink.
> > > > That way we wouldn't block this effort and could discuss more about
> the
> > > > exact properties such a user control plane would need to have. What
> do
> > > you
> > > > think?
> > > >
> > > > Cheers,
> > > > Till
> > > >
> > > > On Wed, Jan 5, 2022 at 7:18 AM Becket Qin <be...@gmail.com>
> > wrote:
> > > >
> > > > > Hi Till,
> > > > >
> > > > > Thanks for the comments and questions. To be clear, I am not saying
> > > that
> > > > > the side-input stream does not work for the dynamic pattern update
> > use
> > > > > case. But I think OC is a better solution. The design goal for CEP
> > > > dynamic
> > > > > pattern is not only make it work, but also make it user friendly
> and
> > > > > extensible. So as a user, I expect the following:
> > > > >
> > > > > - Use CEP with dynamic pattern update without depending on external
> > > > > systems. e.g. updating the pattern by directly talking to the Flink
> > job
> > > > > itself.
> > > > > - Some sort of isolation between patterns. e.g. a pattern update
> > > failure
> > > > > won't cause other running patterns to fail.
> > > > > - Easy to query the currently running patterns in the Flink job.
> > > > > - Extensible to add new features. e.g. apply some pattern to a
> subset
> > > of
> > > > > subtasks. Disable dynamic pattern update during a service window,
> > etc.
> > > > >
> > > > > It looks to me that OC is a more promising way to to achieve the
> > above.
> > > > >
> > > > > Please also see the reply to your questions inline below.
> > > > >
> > > > > > You mentioned that a TM might find out that a pattern is invalid
> > and
> > > > then
> > > > > > it could use the 2-way communication with the JM to tell the
> other
> > > TMs
> > > > > that
> > > > > > the pattern is invalid. How exactly would a TM detect that a
> > pattern
> > > is
> > > > > > invalid at data processing time? And assuming that this is
> possible
> > > > for a
> > > > > > single TM, why can't the other TMs not detect this problem? Is it
> > > > because
> > > > > > the validity of patterns might depend on data that is different
> > > between
> > > > > > TMs?
> > > > >
> > > > >
> > > > > Yes, the TMs are processing different records, so some may
> encounter
> > > > issue
> > > > > while others are running fine, for example, a field may be missing
> > > from a
> > > > > record while the pattern requires it. Even if all the TMs have
> > detected
> > > > the
> > > > > problem, without a channel to report back the issue, the only thing
> > TMs
> > > > can
> > > > > do is either to throw exception and stop processing.
> > > > >
> > > > > You also mentioned that deep-learning-on-flink could benefit from
> an
> > OC
> > > > > > control plane but I couldn't find the referenced link. Would
> > > > > > deep-learning-on-flink like to use OCs as a kind of parameter
> > server?
> > > > > Could
> > > > > > you elaborate on deep-learning-on-flink's usage of such a
> feature?
> > > > >
> > > > >
> > > > > deep-learning-on-flink[1] has a general ML cluster abstraction that
> > can
> > > > run
> > > > > TF / PyTorch etc. This cluster has a ML master role to manage the
> > > > > liveliness of all the ML workers which are python processes running
> > > > > side-by-side with TMs. The ML workers can be PS or Worker of
> > > TensorFlow.
> > > > > For example, if 10 TF worker and 5 TF PS nodes are needed, a Flink
> > UDF
> > > > > operator of parallelism 10 and a Flink Source operator with
> > parallelism
> > > > = 5
> > > > > will be created to run the TF worker and TF PS respectively. All
> the
> > 15
> > > > > nodes running either PS or Worker are managed by the ML master.
> Prior
> > > to
> > > > > OC, the implementation was having a Source operator with
> parallelism
> > =
> > > 1
> > > > to
> > > > > run the master; let the ML workers register themselves to the an
> > > external
> > > > > ZK so the master can discover them. So basically users have to
> build
> > > > their
> > > > > own control plane. With OC, at very least, we no longer need ZK
> > > anymore.
> > > > >
> > > > > Concerning reprocessing command history and repeatable processing
> > > > results I
> > > > > > think there is actually quite a big difference between using a
> > Flink
> > > > > source
> > > > > > vs. offering a REST server that can receive command that are
> > > > distributed
> > > > > > via the OCs. In the former case we can rely on the external
> system
> > to
> > > > > > persist commands whereas in the latter approach we/users have to
> > > > > implement
> > > > > > a storage solution on their own (in the simplest case users will
> > > > probably
> > > > > > store everything in state which might grow indefinitely if stored
> > as
> > > a
> > > > > > changelog).
> > > > >
> > > > >
> > > > > It is true that a Flink Source is easier to provide a change log of
> > > > > patterns. But there are also downsides. The most prominent one is
> > that
> > > in
> > > > > order to update the dynamic pattern, users have to run an external
> > > system
> > > > > for the source to read. Or users have to implement a REST Source
> > taking
> > > > > command directly like a web server. In that case, the service
> > discovery
> > > > is
> > > > > again a problem and needs external dependency.
> > > > > On the other hand, it is not so difficult for OC to store a change
> > log
> > > > > history. Assuming there are 100 pattern updates / day for a CEP job
> > and
> > > > one
> > > > > year of history should be stored. Let's say each pattern change log
> > > entry
> > > > > is 1K bytes. The pattern update change log for the entire year is
> > just
> > > 34
> > > > > MB, which seems quite small. And users can also query the patterns
> in
> > > > > effect via the same endpoint. I think this would provide a good
> > > > out-of-box
> > > > > experience in the vast majority of cases. No external dependencies
> > and
> > > a
> > > > > single REST endpoint. In rare cases where there is a large amount
> of
> > > > > pattern update log. External systems can still be leveraged. One
> > > > potential
> > > > > issue might be that a command that has been received but not
> > > checkpointed
> > > > > yet may got lost if the job fails over. This can be mitigated by
> > > allowing
> > > > > OC to ask JM to trigger a checkpoint (not there yet but may worth
> > > > > thinking), or simply introduce a *PendingCommit* state for a
> pattern
> > > > > indicating it's not committed yet. In the worst case, we can always
> > > > > fallback to store patterns in external systems such as a database.
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Jiangjie (Becket) Qin
> > > > >
> > > > > [1]
> > > > >
> > > > >
> > > >
> > >
> >
> https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
> > > > >
> > > > >
> > > > > On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <trohrmann@apache.org
> >
> > > > wrote:
> > > > >
> > > > > > Hi Becket,
> > > > > >
> > > > > > Thanks for the explanation. While I do agree that a general 2-way
> > > > > > communication pattern would be nice to have, I also believe that
> > this
> > > > > > approach is probably at least one magnitude more complex to
> realize
> > > > than
> > > > > > the side-input approach. Therefore, I really would like to
> > understand
> > > > why
> > > > > > such a mechanism is required for the CEP use case.
> > > > > >
> > > > > > You mentioned that a TM might find out that a pattern is invalid
> > and
> > > > then
> > > > > > it could use the 2-way communication with the JM to tell the
> other
> > > TMs
> > > > > that
> > > > > > the pattern is invalid. How exactly would a TM detect that a
> > pattern
> > > is
> > > > > > invalid at data processing time? And assuming that this is
> possible
> > > > for a
> > > > > > single TM, why can't the other TMs not detect this problem? Is it
> > > > because
> > > > > > the validity of patterns might depend on data that is different
> > > between
> > > > > > TMs?
> > > > > >
> > > > > > You also mentioned that deep-learning-on-flink could benefit from
> > an
> > > OC
> > > > > > control plane but I couldn't find the referenced link. Would
> > > > > > deep-learning-on-flink like to use OCs as a kind of parameter
> > server?
> > > > > Could
> > > > > > you elaborate on deep-learning-on-flink's usage of such a
> feature?
> > > > > >
> > > > > > Concerning reprocessing command history and repeatable processing
> > > > > results I
> > > > > > think there is actually quite a big difference between using a
> > Flink
> > > > > source
> > > > > > vs. offering a REST server that can receive command that are
> > > > distributed
> > > > > > via the OCs. In the former case we can rely on the external
> system
> > to
> > > > > > persist commands whereas in the latter approach we/users have to
> > > > > implement
> > > > > > a storage solution on their own (in the simplest case users will
> > > > probably
> > > > > > store everything in state which might grow indefinitely if stored
> > as
> > > a
> > > > > > changelog).
> > > > > >
> > > > > > Cheers,
> > > > > > Till
> > > > > >
> > > > > > On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com>
> > > > wrote:
> > > > > >
> > > > > > > Hi David,
> > > > > > >
> > > > > > > Thanks for sharing your thoughts. Some quick reply to your
> > > comments:
> > > > > > >
> > > > > > > We're still talking about the "web server based"
> > > > > > > > pattern_processor_discoverer, but what about other use cases?
> > One
> > > > of
> > > > > my
> > > > > > > big
> > > > > > > > concerns is that user's can not really reuse any part of the
> > > Flink
> > > > > > > > ecosystem to implement the discovery logic. For example if
> they
> > > > want
> > > > > to
> > > > > > > > read patterns from Kafka topic, they need to roll their own
> > > > > discoverer
> > > > > > > > based on the vanilla Kafka client. If we're talking about
> > > > > > extensibility,
> > > > > > > > should we also make sure that the existing primitives can be
> > > > reused?
> > > > > > >
> > > > > > >
> > > > > > > KafkaSource is actually more complicated than vanilla
> > KafkaConsumer
> > > > > from
> > > > > > > the perspective of consuming Kafka messages. The KafkaSource
> just
> > > > helps
> > > > > > > make it easier for Flink jobs to process these messages. In
> fact,
> > > > > > > KafkaConsumer is more powerful than KafkaSource in terms of
> > talking
> > > > to
> > > > > > > Kafka. So we are comparing [KafkaConsumer +
> OperatorCoordinator]
> > > and
> > > > > > > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> > > > > > >
> > > > > > > This can be done for the side-input as well by filtering
> invalid
> > > > > patterns
> > > > > > > > before the broadcast. You can also send the invalid patterns
> to
> > > any
> > > > > > side
> > > > > > > > output you want. I have a feeling that we're way too attached
> > to
> > > > the
> > > > > > REST
> > > > > > > > server use case in this discussion. I agree that for that
> case,
> > > > this
> > > > > > > > solution is the most straightforward one.
> > > > > > >
> > > > > > >
> > > > > > > Depending on whether the invalidity is discovered in pattern
> > > > definition
> > > > > > > time or data processing time. e.g. A valid pattern with invalid
> > > data
> > > > > > which
> > > > > > > fails to process can only be detected in data processing time.
> So
> > > the
> > > > > > > pattern won't be filtered out before the broadcast.
> > > > > > >
> > > > > > > I agree that 2-way communication in the "data-flow like" API is
> > > > tricky,
> > > > > > > > because it requires cycles / iterations, which are still not
> > > really
> > > > > > > solved
> > > > > > > > (for a good reason, it's really tough nut to crack). This
> makes
> > > me
> > > > > > think
> > > > > > > > that the OC may be bit of a "incomplete" workaround for not
> > > having
> > > > > > fully
> > > > > > > > working support for iterations.
> > > > > > >
> > > > > > >
> > > > > > > For example I'm not really confident that the checkpointing of
> > the
> > > OC
> > > > > > works
> > > > > > > > correctly right now, because it doesn't seem to require
> > > checkpoint
> > > > > > > barrier
> > > > > > > > alignment as the regular stream inputs. We also don't have a
> > > proper
> > > > > > > support
> > > > > > > > for watermarking (this is again tricky, because of the
> cycle).
> > > > > > >
> > > > > > >
> > > > > > > If we decide to go down this road, should we first address some
> > of
> > > > > these
> > > > > > > > limitations?
> > > > > > >
> > > > > > > I agree. OC is proven to be useful and we should think about
> how
> > to
> > > > > > enhance
> > > > > > > it instead of not using it.
> > > > > > >
> > > > > > > If I understand that correctly, this means only the LATEST
> state
> > of
> > > > the
> > > > > > > > patterns (in other words - patterns that are currently in
> use).
> > > Is
> > > > > this
> > > > > > > > really sufficient for historical re-processing? Can someone
> for
> > > > > example
> > > > > > > > want re-process the data in more of a "temporal join"
> fashion?
> > > Also
> > > > > > AFAIK
> > > > > > > > historical processing in combination with "coordinator
> > > checkpoints"
> > > > > is
> > > > > > > not
> > > > > > > > really something that we currently support of the box, are
> > there
> > > > any
> > > > > > > plans
> > > > > > > > on tackling this (my other concern is that this should not go
> > > > against
> > > > > > the
> > > > > > > > "unified batch & stream processing" efforts)?
> > > > > > >
> > > > > > > I think in this case, the state would contain the entire
> pattern
> > > > update
> > > > > > > history. Not the final state, but the change log. In fact, it
> is
> > > not
> > > > > > > possible to guarantee the correct result unless you have the
> > entire
> > > > > > change
> > > > > > > log. Even with side-input, there still could be late arrivals
> in
> > > the
> > > > > > > pattern update stream, and the only way to correct it is to
> > either
> > > > have
> > > > > > all
> > > > > > > the data reprocessed (with all the pattern change log loaded
> > > upfront)
> > > > > or
> > > > > > > having retraction support.
> > > > > > >
> > > > > > > I can imagine that if this should be a concern, we could move
> the
> > > > > > execution
> > > > > > > > of the OC to the task managers. This also makes me thing,
> that
> > we
> > > > > > > shouldn't
> > > > > > > > make any strong assumptions that the OC will always run in
> the
> > > > > > JobManager
> > > > > > > > (this is especially relevant for the embedded web-server use
> > > case).
> > > > > > >
> > > > > > > This is a very good point. I think we should do this. The
> reason
> > OC
> > > > is
> > > > > in
> > > > > > > JM is based on the assumption that control plane usually have
> > > little
> > > > > > > traffic. But if that is not the case, we should move the OC out
> > of
> > > > JM,
> > > > > > > maybe to TM.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > I think the key topic we are discussing is what the Flink
> control
> > > > plane
> > > > > > > should look like, and CEP is just an example use case. There
> are
> > > > > > basically
> > > > > > > two options:
> > > > > > >
> > > > > > > 1. Using the side-input / broadcast stream
> > > > > > > 2. Using the OperatorCoordinator.
> > > > > > >
> > > > > > > Although we are having this discussion under the context of
> > > > supporting
> > > > > > CEP
> > > > > > > dynamic pattern update, it would be really helpful to reach
> > > agreement
> > > > > on
> > > > > > > the design principle in general of how Flink should handle
> > similar
> > > > > > external
> > > > > > > control demands, a.k.a how to provide a decent control plane in
> > > Flink
> > > > > to
> > > > > > > the users.
> > > > > > >
> > > > > > > Here is my take on these two options, based on the requirements
> > of
> > > a
> > > > > > > control plane.
> > > > > > >
> > > > > > > *Communication Requirements*
> > > > > > > Flink has two kinds of control planes - in-band and
> out-of-band.
> > > > > > > In-band control plane is like watermark and checkpoint marker.
> It
> > > > > > requires
> > > > > > > the entire DAG to be in a consistent state, so the control
> > messages
> > > > > flow
> > > > > > > with the data in one direction. This is a one-way control flow.
> > > > > > > Examples of out-of-band control plane is OC and JM/TM
> > > communication.
> > > > > They
> > > > > > > do not require a global consistency or awareness across the
> > entire
> > > > DAG.
> > > > > > >
> > > > > > > Before OC, neither of these two kinds of control plain was
> > exposed
> > > to
> > > > > the
> > > > > > > users. OC allows the users to leverage the out-of-band control
> > > plane
> > > > so
> > > > > > > they can coordinate across subtasks. This is a more widely used
> > > > control
> > > > > > > flow from user defined operator perspective which requires
> 2-way
> > > > > > > communication.
> > > > > > >
> > > > > > > - side-input stream is one-way communication. Moreover, I
> > don't
> > > > > think
> > > > > > > iteration is the right way to address this. Unlike the
> > > abstraction
> > > > > of
> > > > > > > data
> > > > > > > processing which is a DAG, the control plane may require
> > > > > communication
> > > > > > > between arbitrary two operators in different orders. Using
> > > > > iterations
> > > > > > > may
> > > > > > > end up with an explosion of feedback edges that are not only
> > > > > > > complicated to
> > > > > > > express, but also hard to debug and maintain.
> > > > > > > - OC provides a decent 2-way communication mechanism.
> > > > > > >
> > > > > > >
> > > > > > > *Cost for low traffic use case*
> > > > > > > An important difference between data channel and control
> channel
> > is
> > > > > > traffic
> > > > > > > pattern. Unlike data plane, the control plane is usually idle
> for
> > > the
> > > > > > vast
> > > > > > > majority of the time with occasional control messages.
> > > > > > >
> > > > > > > - One argument to use the side-input / broadcast stream was
> > that
> > > > > users
> > > > > > > can reuse the existing connectors. However, most Flink
> sources
> > > are
> > > > > > > designed
> > > > > > > to handle large throughput of traffic that maintains all the
> > > > > threads,
> > > > > > > network connections, etc. Not to say the external resources
> > such
> > > > as
> > > > > > > Kafka
> > > > > > > topics to store the commands.
> > > > > > > - OC can have a much lower constant cost.
> > > > > > >
> > > > > > >
> > > > > > > *Easy to use*
> > > > > > > Personally speaking, I think the most simple and user-friendly
> > > > > interface
> > > > > > is
> > > > > > > a REST API that accepts control commands.
> > > > > > >
> > > > > > > - One proposal at this point is to have a separate web
> server
> > > > > > > independent of the Flink job. In that case, should users
> > > implement
> > > > > > that
> > > > > > > web
> > > > > > > server? In order to pass the command to the Flink job, does
> > that
> > > > > mean
> > > > > > > users
> > > > > > > should implement a Flink source that can read the commands
> > from
> > > > the
> > > > > > web
> > > > > > > server? Or the web server would send the command to
> something
> > > like
> > > > > > Kafka
> > > > > > > and let the Flink side-input read from there. There seems to
> > be
> > > a
> > > > > lot
> > > > > > > for
> > > > > > > the users to do. And it seems an unnecessarily complicated
> > > system
> > > > to
> > > > > > > build
> > > > > > > to send occasional control messages to a Flink job.
> > > > > > > - OC can simply be reached via the JM REST API.
> > > > > > > - e.g.
> http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > > > > > > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx>
> > would
> > > > > simply
> > > > > > > send the Content to the OC of OP_NAME.
> > > > > > >
> > > > > > > *Work well with checkpoints*
> > > > > > >
> > > > > > > - side-input streams works well with checkpoint, thanks to
> its
> > > > > > > compatibility to the DAG abstraction.
> > > > > > > - The OperatorCoordinator requires more careful design to
> work
> > > > well
> > > > > > with
> > > > > > > checkpoints. The complexity mostly comes from the 2-way
> > > > > communication.
> > > > > > > At
> > > > > > > this point the OperatorCoordinator message delivery semantic
> > may
> > > > not
> > > > > > be
> > > > > > > as
> > > > > > > robust as side-input streams. However, I think this is
> mainly
> > > due
> > > > to
> > > > > > > potential bugs in implementation instead of fundamental
> design
> > > > > > problems.
> > > > > > > Basically the checkpoint semantic should be:
> > > > > > > - The JM will first checkpoint all the
> OperatorCoordinator,
> > > > more
> > > > > > > specifically for each OperatorCoordinator,
> > > > > > > - 1) JM blocks the input queue to stop receiving new
> > > events
> > > > > from
> > > > > > > the subtasks.
> > > > > > > - 2) let all the operator coordinator finish
> processing
> > > all
> > > > > the
> > > > > > > pending events in the OC input queue.
> > > > > > > - 3) flush the OC output queue until all the events
> sent
> > > are
> > > > > > > acknowledged.
> > > > > > > - 3) unblock the input queue, but block the output
> queue
> > > > until
> > > > > > all
> > > > > > > the subtasks of the OC finish checkpoints.
> > > > > > > - The JM starts a normal checkpoint starting from the
> > Source.
> > > > > > > - If an operator has a coordinator, and it has sent
> some
> > > > > events
> > > > > > to
> > > > > > > the OC but has not been acknowledged. These events
> need
> > to
> > > > be
> > > > > > > put into the
> > > > > > > subtasks' checkpoint.
> > > > > > > - After all the subtasks of an operator finishes
> > checkpoint,
> > > > the
> > > > > > > output queue of the corresponding OC can be unblocked.
> > > > > > > It looks that the above protocol would let OC have a clear
> > > > > checkpoint
> > > > > > > semantic. And this complexity seems must for 2-way
> > > communication.
> > > > I
> > > > > > > think
> > > > > > > we are able to hide the above protocol from users by having
> an
> > > > > > abstract
> > > > > > > OC
> > > > > > > implementation.
> > > > > > >
> > > > > > >
> > > > > > > *Reprocess command history and repeatable processing results*
> > > > > > > This seems not something generally required for a control
> plane.
> > > But
> > > > if
> > > > > > the
> > > > > > > control plane changes the data processing behavior, there might
> > be
> > > > some
> > > > > > use
> > > > > > > case. Just like the CEP pattern update. In order to do this,
> > users
> > > > will
> > > > > > > need to provide a full command history to the operators. That
> > > > consists
> > > > > of
> > > > > > > two steps:
> > > > > > >
> > > > > > > 1. get the full command history. (Flink Source V.S. Custom
> > way
> > > to
> > > > > > > retrieve command history.)
> > > > > > > 2. send them to the operators. (Side-input V.S. OC/Operator
> > > > > > > communication)l
> > > > > > >
> > > > > > > I actually don't feel much difference between these two
> options.
> > I
> > > am
> > > > > not
> > > > > > > sure if a Flink source is necessarily simpler than the user
> > > > implemented
> > > > > > > logic. For example, if all the changes are just written in a
> > > database
> > > > > > > table. From the user's perspective, I feel fine with querying
> the
> > > DB
> > > > by
> > > > > > > myself using something like JDBC (or use KafkaConsumer to read
> > the
> > > > > > pattern
> > > > > > > history from a Kafka topic) and send all the pattern change
> > history
> > > > to
> > > > > > the
> > > > > > > operators before they start to process the actual events.
> > > > > > >
> > > > > > > *Stability impact to the Flink Job*
> > > > > > > I agree this is a valid concern. There is only one JM and
> > currently
> > > > OC
> > > > > > runs
> > > > > > > there, which may potentially cause JM crash and result in job
> > > > failure.
> > > > > > > Running in TM may have a less impact. So I think it makes sense
> > to
> > > > run
> > > > > OC
> > > > > > > in TM. However, this is more of how we can implement OC to make
> > it
> > > > more
> > > > > > > robust. It does not forfeit the other semantic and user
> > experience
> > > > > > benefits
> > > > > > > mentioned above.
> > > > > > >
> > > > > > >
> > > > > > > To sum up:
> > > > > > > 1. Regardless of whether CEP chooses OC or side-input stream, a
> > > > decent
> > > > > > > 2-way communication control plane seems really helpful and has
> > been
> > > > > > proven
> > > > > > > by quite a few existing use cases. To me the question is how to
> > > make
> > > > it
> > > > > > > more robust, not whether we should use it or not.
> > > > > > > 2. As for CEP, if we assume OC will be robust enough,
> personally
> > I
> > > > feel
> > > > > > OC
> > > > > > > is a better fit than side-input mainly because of the
> simplicity
> > > and
> > > > > > > extensibility.
> > > > > > >
> > > > > > > Thanks,
> > > > > > >
> > > > > > > Jiangjie (Becket) Qin
> > > > > > >
> > > > > > >
> > > > > > > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dmvk@apache.org
> >
> > > > wrote:
> > > > > > >
> > > > > > > > Hi all,
> > > > > > > >
> > > > > > > > sorry for the late reply, vacation season ;) I'm still not
> 100%
> > > > sold
> > > > > on
> > > > > > > > choosing the OC for this use-case, but on the other hand I
> > don't
> > > > have
> > > > > > > > strong arguments against it. Few more questions / thoughts:
> > > > > > > >
> > > > > > > > We're still talking about the "web server based"
> > > > > > > > pattern_processor_discoverer, but what about other use cases?
> > One
> > > > of
> > > > > my
> > > > > > > big
> > > > > > > > concerns is that user's can not really reuse any part of the
> > > Flink
> > > > > > > > ecosystem to implement the discovery logic. For example if
> they
> > > > want
> > > > > to
> > > > > > > > read patterns from Kafka topic, they need to roll their own
> > > > > discoverer
> > > > > > > > based on the vanilla Kafka client. If we're talking about
> > > > > > extensibility,
> > > > > > > > should we also make sure that the existing primitives can be
> > > > reused?
> > > > > > > >
> > > > > > > > For instance, the example I gave in my previous email seems
> not
> > > > > easily
> > > > > > > > > achievable with side-input / broadcast streams: a single
> > > invalid
> > > > > > > pattern
> > > > > > > > > detected on a TM can be disabled elegantly globally without
> > > > > crashing
> > > > > > > the
> > > > > > > > > entire Flink job.
> > > > > > > >
> > > > > > > >
> > > > > > > > This can be done for the side-input as well by filtering
> > invalid
> > > > > > patterns
> > > > > > > > before the broadcast. You can also send the invalid patterns
> to
> > > any
> > > > > > side
> > > > > > > > output you want. I have a feeling that we're way too attached
> > to
> > > > the
> > > > > > REST
> > > > > > > > server use case in this discussion. I agree that for that
> case,
> > > > this
> > > > > > > > solution is the most straightforward one.
> > > > > > > >
> > > > > > > > OC is a 2-way communication mechanism, i.e. a subtask can
> also
> > > send
> > > > > > > > > OperatorEvent to the coordinator to report its owns status,
> > so
> > > > that
> > > > > > the
> > > > > > > > > coordinator can act accordingly.
> > > > > > > > >
> > > > > > > >
> > > > > > > > I agree that 2-way communication in the "data-flow like" API
> is
> > > > > tricky,
> > > > > > > > because it requires cycles / iterations, which are still not
> > > really
> > > > > > > solved
> > > > > > > > (for a good reason, it's really tough nut to crack). This
> makes
> > > me
> > > > > > think
> > > > > > > > that the OC may be bit of a "incomplete" workaround for not
> > > having
> > > > > > fully
> > > > > > > > working support for iterations.
> > > > > > > >
> > > > > > > > For example I'm not really confident that the checkpointing
> of
> > > the
> > > > OC
> > > > > > > works
> > > > > > > > correctly right now, because it doesn't seem to require
> > > checkpoint
> > > > > > > barrier
> > > > > > > > alignment as the regular stream inputs. We also don't have a
> > > proper
> > > > > > > support
> > > > > > > > for watermarking (this is again tricky, because of the
> cycle).
> > > > > > > >
> > > > > > > > If we decide to go down this road, should we first address
> some
> > > of
> > > > > > these
> > > > > > > > limitations?
> > > > > > > >
> > > > > > > > OperatorCoordinator will checkpoint the full amount of
> > > > > PatternProcessor
> > > > > > > > > data. For the reprocessing of historical data, you can read
> > the
> > > > > > > > > PatternProcessor snapshots saved by this checkpoint from a
> > > > certain
> > > > > > > > > historical checkpoint, and then recreate the historical
> data
> > > > > through
> > > > > > > > these
> > > > > > > > > PatternProcessor snapshots.
> > > > > > > > >
> > > > > > > >
> > > > > > > > If I understand that correctly, this means only the LATEST
> > state
> > > of
> > > > > the
> > > > > > > > patterns (in other words - patterns that are currently in
> use).
> > > Is
> > > > > this
> > > > > > > > really sufficient for historical re-processing? Can someone
> for
> > > > > example
> > > > > > > > want re-process the data in more of a "temporal join"
> fashion?
> > > Also
> > > > > > AFAIK
> > > > > > > > historical processing in combination with "coordinator
> > > checkpoints"
> > > > > is
> > > > > > > not
> > > > > > > > really something that we currently support of the box, are
> > there
> > > > any
> > > > > > > plans
> > > > > > > > on tackling this (my other concern is that this should not go
> > > > against
> > > > > > the
> > > > > > > > "unified batch & stream processing" efforts)?
> > > > > > > >
> > > > > > > > I do agree that having the user defined control logic defined
> > in
> > > > the
> > > > > JM
> > > > > > > > > increases the chance of instability.
> > > > > > > > >
> > > > > > > >
> > > > > > > > I can imagine that if this should be a concern, we could move
> > the
> > > > > > > execution
> > > > > > > > of the OC to the task managers. This also makes me thing,
> that
> > we
> > > > > > > shouldn't
> > > > > > > > make any strong assumptions that the OC will always run in
> the
> > > > > > JobManager
> > > > > > > > (this is especially relevant for the embedded web-server use
> > > case).
> > > > > > > >
> > > > > > > > If an agreement is reached on OperatorCoodinator, I will
> start
> > > the
> > > > > > voting
> > > > > > > > > thread.
> > > > > > > > >
> > > > > > > >
> > > > > > > > As for the vote, I'd would be great if we can wait until the
> > next
> > > > > week
> > > > > > as
> > > > > > > > many people took vacation until end of the year.
> > > > > > > >
> > > > > > > > Overall, I really like the feature, this will be a great
> > addition
> > > > to
> > > > > > > Flink.
> > > > > > > >
> > > > > > > > Best,
> > > > > > > > D.
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <
> > > > > martijn@ververica.com
> > > > > > >
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > > > Hi all,
> > > > > > > > >
> > > > > > > > > I can understand the need for a control plane mechanism.
> I'm
> > > not
> > > > > the
> > > > > > > > > technical go-to person for questions on the
> > > OperatorCoordinator,
> > > > > but
> > > > > > I
> > > > > > > > > would expect that we could offer those interfaces from
> Flink
> > > but
> > > > > > > > shouldn't
> > > > > > > > > recommend running user-code in the JobManager itself. I
> think
> > > the
> > > > > > user
> > > > > > > > code
> > > > > > > > > (like a webserver) should run outside of Flink (like via a
> > > > sidecar)
> > > > > > and
> > > > > > > > use
> > > > > > > > > only the provided interfaces to communicate.
> > > > > > > > >
> > > > > > > > > I would like to get @David Morávek <dm...@apache.org>
> opinion
> > > on
> > > > > the
> > > > > > > > > technical part.
> > > > > > > > >
> > > > > > > > > Best regards,
> > > > > > > > >
> > > > > > > > > Martijn
> > > > > > > > >
> > > > > > > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> > > > > > nicholasjiang@apache.org
> > > > > > > >
> > > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > >> Hi Konstantin, Becket, Martijn,
> > > > > > > > >>
> > > > > > > > >> Thanks for sharing your feedback. What other concerns do
> you
> > > > have
> > > > > > > about
> > > > > > > > >> OperatorCoodinator? If an agreement is reached on
> > > > > > OperatorCoodinator,
> > > > > > > I
> > > > > > > > >> will start the voting thread.
> > > > > > > > >>
> > > > > > > > >> Best,
> > > > > > > > >> Nicholas Jiang
> > > > > > > > >>
> > > > > > > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > > > > > > >> > Hi Konstantin,
> > > > > > > > >> >
> > > > > > > > >> > Thanks for sharing your thoughts. Please see the reply
> > > inline
> > > > > > below.
> > > > > > > > >> >
> > > > > > > > >> > Thanks,
> > > > > > > > >> >
> > > > > > > > >> > Jiangjie (Becket) Qin
> > > > > > > > >> >
> > > > > > > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> > > > > > knaufk@apache.org
> > > > > > > >
> > > > > > > > >> wrote:
> > > > > > > > >> >
> > > > > > > > >> > > Hi Becket, Hi Nicholas,
> > > > > > > > >> > >
> > > > > > > > >> > > Thanks for joining the discussion.
> > > > > > > > >> > >
> > > > > > > > >> > > 1 ) Personally, I would argue that we should only run
> > user
> > > > > code
> > > > > > in
> > > > > > > > the
> > > > > > > > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems
> > > wrong
> > > > to
> > > > > > me
> > > > > > > to
> > > > > > > > >> > > encourage users to e.g. run a webserver on the
> > Jobmanager,
> > > > or
> > > > > > > > >> continuously
> > > > > > > > >> > > read patterns from a Kafka Topic on the Jobmanager,
> but
> > > both
> > > > > of
> > > > > > > > these
> > > > > > > > >> I see
> > > > > > > > >> > > happening with the current design. We've had lots of
> > > issues
> > > > > with
> > > > > > > > >> > > classloading leaks and other stability issues on the
> > > > > Jobmanager
> > > > > > > and
> > > > > > > > >> making
> > > > > > > > >> > > this more complicated, if there is another way, seems
> > > > > > unnecessary.
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > I think the key question here is what primitive does
> Flink
> > > > > provide
> > > > > > > to
> > > > > > > > >> > facilitate the user implementation of their own control
> > > logic
> > > > /
> > > > > > > > control
> > > > > > > > >> > plane? It looks that previously, Flink assumes that all
> > the
> > > > user
> > > > > > > logic
> > > > > > > > >> is
> > > > > > > > >> > just data processing logic without any control /
> > > coordination
> > > > > > > > >> requirements.
> > > > > > > > >> > However, it turns out that a decent control plane
> > > abstraction
> > > > is
> > > > > > > > >> required
> > > > > > > > >> > in association with the data processing logic in many
> > cases,
> > > > > > > including
> > > > > > > > >> > Source / Sink and other user defined operators in
> general.
> > > The
> > > > > > fact
> > > > > > > > >> that we
> > > > > > > > >> > ended up with adding the SplitEnumerator and
> > GlobalCommitter
> > > > are
> > > > > > > just
> > > > > > > > >> two
> > > > > > > > >> > examples of the demand of such coordination among user
> > > defined
> > > > > > > logics.
> > > > > > > > >> > There are other cases that we see in ecosystem projects,
> > > such
> > > > as
> > > > > > > > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > > > > > > > >> >
> > > > > > > > >> > Such control plane primitives are critical to the
> > > > extensibility
> > > > > > of a
> > > > > > > > >> > project. If we look at other projects, exposing such
> > control
> > > > > plane
> > > > > > > > >> logic is
> > > > > > > > >> > quite common. For example, Hadoop ended up with exposing
> > > YARN
> > > > > as a
> > > > > > > > >> public
> > > > > > > > >> > API to the users, which is extremely popular. Kafka
> > > consumers
> > > > > > > exposed
> > > > > > > > >> the
> > > > > > > > >> > consumer group rebalance logic to the users via
> > > > > > > > >> ConsumerPartitionAssigner,
> > > > > > > > >> > which is also a control plane primitive.
> > > > > > > > >> >
> > > > > > > > >> > To me it is more important to think about how we can
> > improve
> > > > the
> > > > > > > > >> stability
> > > > > > > > >> > of such a control plane mechanism, instead of simply
> > saying
> > > no
> > > > > to
> > > > > > > the
> > > > > > > > >> users.
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > > 2) In addition, I suspect that, over time we will have
> > to
> > > > > > > implement
> > > > > > > > >> all the
> > > > > > > > >> > > functionality that regular sources already provide
> > around
> > > > > > > > consistency
> > > > > > > > >> > > (watermarks, checkpointing) for the
> > > > > PatternProcessorCoordinator,
> > > > > > > > too.
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > I think OperatorCoordinator should have a generic
> > > > communication
> > > > > > > > >> mechanism
> > > > > > > > >> > for all the operators, not specific to Source. We should
> > > > > probably
> > > > > > > have
> > > > > > > > >> an
> > > > > > > > >> > AbstractOperatorCoordinator help dealing with the
> > > > communication
> > > > > > > layer,
> > > > > > > > >> and
> > > > > > > > >> > leave the state maintenance and event handling logic to
> > the
> > > > user
> > > > > > > code.
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > > 3) I understand that running on the Jobmanager is
> easier
> > > if
> > > > > you
> > > > > > > want
> > > > > > > > >> to
> > > > > > > > >> > > launch a REST server directly. Here my question would
> > be:
> > > > does
> > > > > > > this
> > > > > > > > >> really
> > > > > > > > >> > > need to be solved inside of Flink or couldn't you
> start
> > a
> > > > > > > webserver
> > > > > > > > >> next to
> > > > > > > > >> > > Flink? If we start using the Jobmanager as a REST
> server
> > > > users
> > > > > > > will
> > > > > > > > >> expect
> > > > > > > > >> > > that e.g. it is highly available and can be load
> > balanced
> > > > and
> > > > > we
> > > > > > > > >> quickly
> > > > > > > > >> > > need to think about aspects that we never wanted to
> > think
> > > > > about
> > > > > > in
> > > > > > > > the
> > > > > > > > >> > > context of a Flink Jobmanager.
> > > > > > > > >> > >
> > > > > > > > >> >
> > > > > > > > >> > I think the REST API is just for receiving commands
> > > targeting
> > > > a
> > > > > > > > running
> > > > > > > > >> > Flink job. If the job fails, the REST API would be
> > useless.
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > > So, can you elaborate a bit more, why a
> > > side-input/broadcast
> > > > > > > stream
> > > > > > > > is
> > > > > > > > >> > >
> > > > > > > > >> > > a) more difficult
> > > > > > > > >> > > b) has vague semantics (To me semantics of a
> > stream-stream
> > > > > seem
> > > > > > > > >> clearer
> > > > > > > > >> > > when it comes to out-of-orderness, late data,
> > reprocessing
> > > > or
> > > > > > > batch
> > > > > > > > >> > > execution mode.)
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > I do agree that having the user defined control logic
> > > defined
> > > > in
> > > > > > the
> > > > > > > > JM
> > > > > > > > >> > increases the chance of instability. In that case, we
> may
> > > > think
> > > > > of
> > > > > > > > other
> > > > > > > > >> > solutions and I am fully open to that. But the
> side-input
> > /
> > > > > > > broadcast
> > > > > > > > >> > stream seems more like a bandaid instead of a carefully
> > > > designed
> > > > > > > > control
> > > > > > > > >> > plane mechanism.
> > > > > > > > >> >
> > > > > > > > >> > A decent control plane requires two-way communication,
> so
> > > > > > > information
> > > > > > > > >> can
> > > > > > > > >> > be reported / collected from the entity being
> controlled,
> > > and
> > > > > the
> > > > > > > > >> > coordinator / controller can send decisions or commands
> to
> > > the
> > > > > > > > entities
> > > > > > > > >> > accordingly, just like our TM / JM communication. IIUC,
> > this
> > > > is
> > > > > > not
> > > > > > > > >> > achievable with the existing side-input / broadcast
> stream
> > > as
> > > > > both
> > > > > > > of
> > > > > > > > >> them
> > > > > > > > >> > are one-way communication mechanisms. For instance, the
> > > > example
> > > > > I
> > > > > > > gave
> > > > > > > > >> in
> > > > > > > > >> > my previous email seems not easily achievable with
> > > side-input
> > > > /
> > > > > > > > >> broadcast
> > > > > > > > >> > streams: a single invalid pattern detected on a TM can
> be
> > > > > disabled
> > > > > > > > >> > elegantly globally without crashing the entire Flink
> job.
> > > > > > > > >> >
> > > > > > > > >> >
> > > > > > > > >> > > Cheers,
> > > > > > > > >> > >
> > > > > > > > >> > > Konstantin
> > > > > > > > >> > >
> > > > > > > > >> > >
> > > > > > > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> > > > > > becket.qin@gmail.com
> > > > > > > >
> > > > > > > > >> wrote:
> > > > > > > > >> > >
> > > > > > > > >> > > > Hi folks,
> > > > > > > > >> > > >
> > > > > > > > >> > > > I just finished reading the previous emails. It was
> a
> > > good
> > > > > > > > >> discussion.
> > > > > > > > >> > > Here
> > > > > > > > >> > > > are my two cents:
> > > > > > > > >> > > >
> > > > > > > > >> > > > *Is OperatorCoordinator a public API?*
> > > > > > > > >> > > > Regarding the OperatorCoordinator, although it is
> > marked
> > > > as
> > > > > > > > internal
> > > > > > > > >> > > > interface at this point, I intended to make it a
> > public
> > > > > > > interface
> > > > > > > > >> when
> > > > > > > > >> > > add
> > > > > > > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> > > > > > communication
> > > > > > > > >> mechanism
> > > > > > > > >> > > > that enables many use cases, Source / Sink / TF on
> > > Flink /
> > > > > CEP
> > > > > > > > here
> > > > > > > > >> > > again.
> > > > > > > > >> > > > To my understanding, OC was marked as internal
> because
> > > we
> > > > > > think
> > > > > > > it
> > > > > > > > >> is not
> > > > > > > > >> > > > stable enough yet. We may need to fortify the
> > > > OperatorEvent
> > > > > > > > delivery
> > > > > > > > >> > > > semantic a little bit so it works well with
> checkpoint
> > > in
> > > > > > > general.
> > > > > > > > >> > > >
> > > > > > > > >> > > > I think it is a valid concern that user code running
> > in
> > > JM
> > > > > may
> > > > > > > > cause
> > > > > > > > >> > > > instability. However, not providing this
> communication
> > > > > > mechanism
> > > > > > > > >> only
> > > > > > > > >> > > makes
> > > > > > > > >> > > > a lot of use case even harder to implement. So it
> > seems
> > > > that
> > > > > > > > having
> > > > > > > > >> the
> > > > > > > > >> > > OC
> > > > > > > > >> > > > exposed to end users brings more benefits than harm
> to
> > > > > Flink.
> > > > > > At
> > > > > > > > >> the end
> > > > > > > > >> > > of
> > > > > > > > >> > > > the day, users have many ways to crash a Flink job
> if
> > > they
> > > > > do
> > > > > > > not
> > > > > > > > >> write
> > > > > > > > >> > > > proper code. So making those who know what they do
> > happy
> > > > > seems
> > > > > > > > more
> > > > > > > > >> > > > important here.
> > > > > > > > >> > > >
> > > > > > > > >> > > > *OperatorCoordinator V.S. side-input / broadcast
> > stream*
> > > > > > > > >> > > > I think both of them can achieve the goal of dynamic
> > > > > patterns.
> > > > > > > The
> > > > > > > > >> main
> > > > > > > > >> > > > difference is the extensibility.
> > > > > > > > >> > > >
> > > > > > > > >> > > > OC is a 2-way communication mechanism, i.e. a
> subtask
> > > can
> > > > > also
> > > > > > > > send
> > > > > > > > >> > > > OperatorEvent to the coordinator to report its owns
> > > > status,
> > > > > so
> > > > > > > > that
> > > > > > > > >> the
> > > > > > > > >> > > > coordinator can act accordingly. This is sometimes
> > > useful.
> > > > > For
> > > > > > > > >> example, a
> > > > > > > > >> > > > single invalid pattern can be disabled elegantly
> > without
> > > > > > > crashing
> > > > > > > > >> the
> > > > > > > > >> > > > entire Flink job. In the future, if we allow users
> to
> > > send
> > > > > > > > external
> > > > > > > > >> > > command
> > > > > > > > >> > > > to OC via JM, a default self-contained
> implementation
> > > can
> > > > > just
> > > > > > > > >> update the
> > > > > > > > >> > > > pattern via the REST API without external
> > dependencies.
> > > > > > > > >> > > >
> > > > > > > > >> > > > Another reason I personally prefer OC is because it
> is
> > > an
> > > > > > > explicit
> > > > > > > > >> > > control
> > > > > > > > >> > > > plain mechanism, where as the side-input / broadcast
> > > > stream
> > > > > > has
> > > > > > > > are
> > > > > > > > >> more
> > > > > > > > >> > > > vague semantic.
> > > > > > > > >> > > >
> > > > > > > > >> > > > Thanks,
> > > > > > > > >> > > >
> > > > > > > > >> > > > Jiangjie (Becket) Qin
> > > > > > > > >> > > >
> > > > > > > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> > > > > > dmvk@apache.org>
> > > > > > > > >> wrote:
> > > > > > > > >> > > >
> > > > > > > > >> > > > > Hi Yunfeng,
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > thanks for drafting this FLIP, this will be a
> great
> > > > > addition
> > > > > > > > into
> > > > > > > > >> the
> > > > > > > > >> > > CEP
> > > > > > > > >> > > > > toolbox!
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > Apart from running user code in JM, which want to
> > > avoid
> > > > in
> > > > > > > > >> general, I'd
> > > > > > > > >> > > > > have one more another concern about using the
> > > > > > > > OperatorCoordinator
> > > > > > > > >> and
> > > > > > > > >> > > > that
> > > > > > > > >> > > > > is re-processing of the historical data. Any
> > thoughts
> > > > > about
> > > > > > > how
> > > > > > > > >> this
> > > > > > > > >> > > will
> > > > > > > > >> > > > > work with the OC?
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > I have a slight feeling that a side-input (custom
> > > > source /
> > > > > > > > >> operator +
> > > > > > > > >> > > > > broadcast) would a better fit for this case. This
> > > would
> > > > > > > simplify
> > > > > > > > >> the
> > > > > > > > >> > > > > consistency concerns (watermarks + pushback) and
> the
> > > > > > > > >> re-processing of
> > > > > > > > >> > > > > historical data.
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > Best,
> > > > > > > > >> > > > > D.
> > > > > > > > >> > > > >
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > > > > > > >> > > nicholasjiang@apache.org
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > wrote:
> > > > > > > > >> > > > >
> > > > > > > > >> > > > > > Hi Konstantin, Martijn
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > Thanks for the detailed feedback in the
> > discussion.
> > > > > What I
> > > > > > > > >> still have
> > > > > > > > >> > > > > left
> > > > > > > > >> > > > > > to answer/reply to:
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > -- Martijn: Just to be sure, this indeed would
> > mean
> > > > that
> > > > > > if
> > > > > > > > for
> > > > > > > > >> > > > whatever
> > > > > > > > >> > > > > > reason the heartbeat timeout, it would crash the
> > > job,
> > > > > > right?
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > IMO, if for whatever reason the heartbeat
> timeout,
> > > it
> > > > > > > couldn't
> > > > > > > > >> check
> > > > > > > > >> > > > the
> > > > > > > > >> > > > > > PatternProcessor consistency between the
> > > > > > OperatorCoordinator
> > > > > > > > >> and the
> > > > > > > > >> > > > > > subtasks so that the job would be crashed.
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > -- Konstantin: What I was concerned about is
> that
> > we
> > > > > > > basically
> > > > > > > > >> let
> > > > > > > > >> > > > users
> > > > > > > > >> > > > > > run a UserFunction in the OperatorCoordinator,
> > which
> > > > it
> > > > > > does
> > > > > > > > >> not seem
> > > > > > > > >> > > > to
> > > > > > > > >> > > > > > have been designed for.
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > In general, we have reached an agreement on the
> > > design
> > > > > of
> > > > > > > this
> > > > > > > > >> FLIP,
> > > > > > > > >> > > > but
> > > > > > > > >> > > > > > there are some concerns on the
> > OperatorCoordinator,
> > > > > about
> > > > > > > > >> whether
> > > > > > > > >> > > > > basically
> > > > > > > > >> > > > > > let users run a UserFunction in the
> > > > OperatorCoordinator
> > > > > is
> > > > > > > > >> designed
> > > > > > > > >> > > for
> > > > > > > > >> > > > > > OperatorCoordinator. We would like to invite
> > Becket
> > > > Qin
> > > > > > who
> > > > > > > is
> > > > > > > > >> the
> > > > > > > > >> > > > author
> > > > > > > > >> > > > > > of OperatorCoordinator to help us to answer this
> > > > > concern.
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > Best,
> > > > > > > > >> > > > > > Nicholas Jiang
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > > > > > > >> > > > > > > Hi all,
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > Really like the discussion on this topic
> moving
> > > > > > forward. I
> > > > > > > > >> really
> > > > > > > > >> > > > think
> > > > > > > > >> > > > > > > this feature will be much appreciated by the
> > Flink
> > > > > > users.
> > > > > > > > >> What I
> > > > > > > > >> > > > still
> > > > > > > > >> > > > > > have
> > > > > > > > >> > > > > > > left to answer/reply to:
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > -- Good point. If for whatever reason the
> > > different
> > > > > > > > >> taskmanagers
> > > > > > > > >> > > > can't
> > > > > > > > >> > > > > > get
> > > > > > > > >> > > > > > > the latest rule, the Operator Coordinator
> could
> > > > send a
> > > > > > > > >> heartbeat to
> > > > > > > > >> > > > all
> > > > > > > > >> > > > > > > taskmanagers with the latest rules and check
> the
> > > > > > heartbeat
> > > > > > > > >> response
> > > > > > > > >> > > > > from
> > > > > > > > >> > > > > > > all the taskmanagers whether the latest rules
> of
> > > the
> > > > > > > > >> taskmanager is
> > > > > > > > >> > > > > equal
> > > > > > > > >> > > > > > > to these of the Operator Coordinator.
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > Just to be sure, this indeed would mean that
> if
> > > for
> > > > > > > whatever
> > > > > > > > >> reason
> > > > > > > > >> > > > the
> > > > > > > > >> > > > > > > heartbeat timeout, it would crash the job,
> > right?
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > -- We have consided about the solution
> mentioned
> > > > > above.
> > > > > > In
> > > > > > > > >> this
> > > > > > > > >> > > > > > solution, I
> > > > > > > > >> > > > > > > have some questions about how to guarantee the
> > > > > > consistency
> > > > > > > > of
> > > > > > > > >> the
> > > > > > > > >> > > > rule
> > > > > > > > >> > > > > > > between each TaskManager. By having a
> coodinator
> > > in
> > > > > the
> > > > > > > > >> JobManager
> > > > > > > > >> > > to
> > > > > > > > >> > > > > > > centrally manage the latest rules, the latest
> > > rules
> > > > of
> > > > > > all
> > > > > > > > >> > > > TaskManagers
> > > > > > > > >> > > > > > are
> > > > > > > > >> > > > > > > consistent with those of the JobManager, so as
> > to
> > > > > avoid
> > > > > > > the
> > > > > > > > >> > > > > > inconsistencies
> > > > > > > > >> > > > > > > that may be encountered in the above solution.
> > Can
> > > > you
> > > > > > > > >> introduce
> > > > > > > > >> > > how
> > > > > > > > >> > > > > this
> > > > > > > > >> > > > > > > solution guarantees the consistency of the
> > rules?
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > The consistency that we could guarantee was
> > based
> > > on
> > > > > how
> > > > > > > > >> often each
> > > > > > > > >> > > > > > > TaskManager would do a refresh and how often
> we
> > > > would
> > > > > > > > accept a
> > > > > > > > >> > > > refresh
> > > > > > > > >> > > > > to
> > > > > > > > >> > > > > > > fail. We set the refresh time to a relatively
> > > short
> > > > > one
> > > > > > > (30
> > > > > > > > >> > > seconds)
> > > > > > > > >> > > > > and
> > > > > > > > >> > > > > > > maximum failures to 3. That meant that we
> could
> > > > > > guarantee
> > > > > > > > that
> > > > > > > > >> > > rules
> > > > > > > > >> > > > > > would
> > > > > > > > >> > > > > > > be updated in < 2 minutes or else the job
> would
> > > > crash.
> > > > > > > That
> > > > > > > > >> was
> > > > > > > > >> > > > > > sufficient
> > > > > > > > >> > > > > > > for our use cases. This also really depends on
> > how
> > > > big
> > > > > > > your
> > > > > > > > >> cluster
> > > > > > > > >> > > > > is. I
> > > > > > > > >> > > > > > > can imagine that if you have a large scale
> > cluster
> > > > > that
> > > > > > > you
> > > > > > > > >> want to
> > > > > > > > >> > > > > run,
> > > > > > > > >> > > > > > > you don't want to DDOS the backend system
> where
> > > you
> > > > > have
> > > > > > > > your
> > > > > > > > >> rules
> > > > > > > > >> > > > > > stored.
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > -- In summary, the current design is that
> > > JobManager
> > > > > > tells
> > > > > > > > all
> > > > > > > > >> > > > > > TaskManagers
> > > > > > > > >> > > > > > > the latest rules through OperatorCoodinator,
> and
> > > > will
> > > > > > > > >> initiate a
> > > > > > > > >> > > > > > heartbeat
> > > > > > > > >> > > > > > > to check whether the latest rules on each
> > > > TaskManager
> > > > > > are
> > > > > > > > >> > > consistent.
> > > > > > > > >> > > > > We
> > > > > > > > >> > > > > > > will describe how to deal with the Failover
> > > scenario
> > > > > in
> > > > > > > more
> > > > > > > > >> detail
> > > > > > > > >> > > > on
> > > > > > > > >> > > > > > FLIP.
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > Thanks for that. I think having the JobManager
> > > tell
> > > > > the
> > > > > > > > >> > > TaskManagers
> > > > > > > > >> > > > > the
> > > > > > > > >> > > > > > > applicable rules would indeed end up being the
> > > best
> > > > > > > design.
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > -- about the concerns around consistency
> raised
> > by
> > > > > > > Martijn:
> > > > > > > > I
> > > > > > > > >> > > think a
> > > > > > > > >> > > > > lot
> > > > > > > > >> > > > > > > of those can be mitigated by using an event
> time
> > > > > > timestamp
> > > > > > > > >> from
> > > > > > > > >> > > which
> > > > > > > > >> > > > > the
> > > > > > > > >> > > > > > > rules take effect. The reprocessing scenario,
> > for
> > > > > > example,
> > > > > > > > is
> > > > > > > > >> > > covered
> > > > > > > > >> > > > > by
> > > > > > > > >> > > > > > > this. If a pattern processor should become
> > active
> > > as
> > > > > > soon
> > > > > > > as
> > > > > > > > >> > > > possible,
> > > > > > > > >> > > > > > > there will still be inconsistencies between
> > > > > > Taskmanagers,
> > > > > > > > but
> > > > > > > > >> "as
> > > > > > > > >> > > > soon
> > > > > > > > >> > > > > as
> > > > > > > > >> > > > > > > possible" is vague anyway, which is why I
> think
> > > > that's
> > > > > > ok.
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > I think an event timestamp is indeed a really
> > > > > important
> > > > > > > one.
> > > > > > > > >> We
> > > > > > > > >> > > also
> > > > > > > > >> > > > > used
> > > > > > > > >> > > > > > > that in my previous role, with the
> > > > > > ruleActivationTimestamp
> > > > > > > > >> compared
> > > > > > > > >> > > > to
> > > > > > > > >> > > > > > > eventtime (well, actually we used Kafka
> > logAppend
> > > > time
> > > > > > > > because
> > > > > > > > >> > > > > > > eventtime wasn't always properly set so we
> used
> > > that
> > > > > > time
> > > > > > > to
> > > > > > > > >> > > > overwrite
> > > > > > > > >> > > > > > the
> > > > > > > > >> > > > > > > eventtime from the event itself).
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > Best regards,
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > Martijn
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin
> Knauf <
> > > > > > > > >> knaufk@apache.org>
> > > > > > > > >> > > > > > wrote:
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > about the concerns around consistency raised
> > by
> > > > > > > Martijn: I
> > > > > > > > >> think
> > > > > > > > >> > > a
> > > > > > > > >> > > > > lot
> > > > > > > > >> > > > > > of
> > > > > > > > >> > > > > > > > those can be mitigated by using an event
> time
> > > > > > timestamp
> > > > > > > > from
> > > > > > > > >> > > which
> > > > > > > > >> > > > > the
> > > > > > > > >> > > > > > > > rules take effect. The reprocessing
> scenario,
> > > for
> > > > > > > example,
> > > > > > > > >> is
> > > > > > > > >> > > > covered
> > > > > > > > >> > > > > > by
> > > > > > > > >> > > > > > > > this. If a pattern processor should become
> > > active
> > > > as
> > > > > > > soon
> > > > > > > > as
> > > > > > > > >> > > > > possible,
> > > > > > > > >> > > > > > > > there will still be inconsistencies between
> > > > > > > Taskmanagers,
> > > > > > > > >> but "as
> > > > > > > > >> > > > > soon
> > > > > > > > >> > > > > > as
> > > > > > > > >> > > > > > > > possible" is vague anyway, which is why I
> > think
> > > > > that's
> > > > > > > ok.
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > about naming: The naming with
> > "PatternProcessor"
> > > > > > sounds
> > > > > > > > >> good to
> > > > > > > > >> > > me.
> > > > > > > > >> > > > > > Final
> > > > > > > > >> > > > > > > > nit: I would go for CEP#patternProccessors,
> > > which
> > > > > > would
> > > > > > > be
> > > > > > > > >> > > > consistent
> > > > > > > > >> > > > > > with
> > > > > > > > >> > > > > > > > CEP#pattern.
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > I am not sure about one of the rejected
> > > > > alternatives:
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > > Have each subtask of an operator make the
> > > update
> > > > > on
> > > > > > > > their
> > > > > > > > >> own
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > -
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > It is hard to achieve consistency.
> > > > > > > > >> > > > > > > > -
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > Though the time interval that each
> > subtask
> > > > > makes
> > > > > > > the
> > > > > > > > >> update
> > > > > > > > >> > > > can
> > > > > > > > >> > > > > > be
> > > > > > > > >> > > > > > > > the same, the absolute time they make
> > the
> > > > > update
> > > > > > > > >> might be
> > > > > > > > >> > > > > > different.
> > > > > > > > >> > > > > > > > For
> > > > > > > > >> > > > > > > > example, one makes updates at 10:00,
> > > 10:05,
> > > > > etc,
> > > > > > > > while
> > > > > > > > >> > > > another
> > > > > > > > >> > > > > > does
> > > > > > > > >> > > > > > > > it at
> > > > > > > > >> > > > > > > > 10:01, 10:06. In this case the
> subtasks
> > > > might
> > > > > > > never
> > > > > > > > >> > > > processing
> > > > > > > > >> > > > > > data
> > > > > > > > >> > > > > > > > with
> > > > > > > > >> > > > > > > > the same set of pattern processors.
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > I would have thought that it is quite easy
> to
> > > poll
> > > > > for
> > > > > > > the
> > > > > > > > >> rules
> > > > > > > > >> > > > from
> > > > > > > > >> > > > > > each
> > > > > > > > >> > > > > > > > Subtask at *about *the same time. So, this
> > alone
> > > > > does
> > > > > > > not
> > > > > > > > >> seem to
> > > > > > > > >> > > > be
> > > > > > > > >> > > > > > > > enough to rule out this option. I've looped
> in
> > > > David
> > > > > > > > >> Moravek to
> > > > > > > > >> > > get
> > > > > > > > >> > > > > his
> > > > > > > > >> > > > > > > > opinion of the additional load imposed on
> the
> > > JM.
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > Thanks,
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > Konstantin
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas
> > Jiang <
> > > > > > > > >> > > > > > nicholasjiang@apache.org>
> > > > > > > > >> > > > > > > > wrote:
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > > Hi Yue,
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > Thanks for your feedback of the FLIP. I
> have
> > > > > > addressed
> > > > > > > > >> your
> > > > > > > > >> > > > > > questions and
> > > > > > > > >> > > > > > > > > made a corresponding explanation as
> follows:
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > > > >> > > > to
> > > > > > > > >> > > > > > > > update
> > > > > > > > >> > > > > > > > > the rules, will it increase the load of
> JM?
> > > For
> > > > > > > example,
> > > > > > > > >> if the
> > > > > > > > >> > > > > user
> > > > > > > > >> > > > > > > > wants
> > > > > > > > >> > > > > > > > > the updated rule to take effect
> > immediately,,
> > > > > which
> > > > > > > > means
> > > > > > > > >> that
> > > > > > > > >> > > we
> > > > > > > > >> > > > > > need to
> > > > > > > > >> > > > > > > > > set a shorter check interval or there is
> > > another
> > > > > > > > scenario
> > > > > > > > >> when
> > > > > > > > >> > > > > users
> > > > > > > > >> > > > > > > > rarely
> > > > > > > > >> > > > > > > > > update the pattern, will the
> > > > > > > PatternProcessoerDiscoverer
> > > > > > > > >> be in
> > > > > > > > >> > > > most
> > > > > > > > >> > > > > > of
> > > > > > > > >> > > > > > > > the
> > > > > > > > >> > > > > > > > > time Do useless checks ? Will a lazy
> update
> > > mode
> > > > > > could
> > > > > > > > be
> > > > > > > > >> used,
> > > > > > > > >> > > > > > which the
> > > > > > > > >> > > > > > > > > pattern only be updated when triggered by
> > the
> > > > > user,
> > > > > > > and
> > > > > > > > do
> > > > > > > > >> > > > nothing
> > > > > > > > >> > > > > at
> > > > > > > > >> > > > > > > > other
> > > > > > > > >> > > > > > > > > times?
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > PatternProcessoerDiscoverer is a
> > user-defined
> > > > > > > interface
> > > > > > > > to
> > > > > > > > >> > > > discover
> > > > > > > > >> > > > > > the
> > > > > > > > >> > > > > > > > > PatternProcessor updates. Periodically
> > > checking
> > > > > the
> > > > > > > > >> > > > > PatternProcessor
> > > > > > > > >> > > > > > in
> > > > > > > > >> > > > > > > > the
> > > > > > > > >> > > > > > > > > database is a implementation of the
> > > > > > > > >> PatternProcessoerDiscoverer
> > > > > > > > >> > > > > > > > interface,
> > > > > > > > >> > > > > > > > > which is that periodically querys all the
> > > > > > > > PatternProcessor
> > > > > > > > >> > > table
> > > > > > > > >> > > > in
> > > > > > > > >> > > > > > > > certain
> > > > > > > > >> > > > > > > > > interval. This implementation indeeds has
> > the
> > > > > > useless
> > > > > > > > >> checks,
> > > > > > > > >> > > and
> > > > > > > > >> > > > > > could
> > > > > > > > >> > > > > > > > > directly integrates the changelog of the
> > > table.
> > > > In
> > > > > > > > >> addition, in
> > > > > > > > >> > > > > > addition
> > > > > > > > >> > > > > > > > to
> > > > > > > > >> > > > > > > > > the implementation of periodically
> checking
> > > the
> > > > > > > > database,
> > > > > > > > >> there
> > > > > > > > >> > > > are
> > > > > > > > >> > > > > > other
> > > > > > > > >> > > > > > > > > implementations such as the
> PatternProcessor
> > > > that
> > > > > > > > provides
> > > > > > > > >> > > > Restful
> > > > > > > > >> > > > > > > > services
> > > > > > > > >> > > > > > > > > to receive updates.
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > -- I still have some confusion about how
> > Key
> > > > > > > Generating
> > > > > > > > >> > > > Opertator
> > > > > > > > >> > > > > > and
> > > > > > > > >> > > > > > > > > CepOperator (Pattern Matching & Processing
> > > > > Operator)
> > > > > > > > work
> > > > > > > > >> > > > together.
> > > > > > > > >> > > > > > If
> > > > > > > > >> > > > > > > > > there are N PatternProcessors, will the
> Key
> > > > > > Generating
> > > > > > > > >> > > Opertator
> > > > > > > > >> > > > > > > > generate N
> > > > > > > > >> > > > > > > > > keyedStreams, and then N CepOperator would
> > > > process
> > > > > > > each
> > > > > > > > >> Key
> > > > > > > > >> > > > > > separately ?
> > > > > > > > >> > > > > > > > Or
> > > > > > > > >> > > > > > > > > every CepOperator Task would process all
> > > > patterns,
> > > > > > if
> > > > > > > > so,
> > > > > > > > >> does
> > > > > > > > >> > > > the
> > > > > > > > >> > > > > > key
> > > > > > > > >> > > > > > > > type
> > > > > > > > >> > > > > > > > > in each PatternProcessor need to be the
> > same?
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > Firstly the Pattern Matching & Processing
> > > > Operator
> > > > > > is
> > > > > > > > not
> > > > > > > > >> the
> > > > > > > > >> > > > > > CepOperator
> > > > > > > > >> > > > > > > > > at present, because CepOperator mechanism
> is
> > > > based
> > > > > > on
> > > > > > > > the
> > > > > > > > >> > > > NFAState.
> > > > > > > > >> > > > > > > > > Secondly if there are N PatternProcessors,
> > the
> > > > Key
> > > > > > > > >> Generating
> > > > > > > > >> > > > > > Opertator
> > > > > > > > >> > > > > > > > > combines all the keyedStreams with keyBy()
> > > > > > operation,
> > > > > > > > >> thus the
> > > > > > > > >> > > > > > Pattern
> > > > > > > > >> > > > > > > > > Matching & Processing Operator would
> process
> > > all
> > > > > the
> > > > > > > > >> patterns.
> > > > > > > > >> > > In
> > > > > > > > >> > > > > > other
> > > > > > > > >> > > > > > > > > words, the KeySelector of the
> > PatternProcessor
> > > > is
> > > > > > used
> > > > > > > > >> for the
> > > > > > > > >> > > > Key
> > > > > > > > >> > > > > > > > > Generating Opertator, and the Pattern and
> > > > > > > > >> > > PatternProceessFunction
> > > > > > > > >> > > > > of
> > > > > > > > >> > > > > > the
> > > > > > > > >> > > > > > > > > PatternProcessor are used for the Pattern
> > > > > Matching &
> > > > > > > > >> Processing
> > > > > > > > >> > > > > > Operator.
> > > > > > > > >> > > > > > > > > Lastly the key type in each
> PatternProcessor
> > > is
> > > > > the
> > > > > > > > same,
> > > > > > > > >> > > > regarded
> > > > > > > > >> > > > > as
> > > > > > > > >> > > > > > > > > Object type.
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > -- Maybe need to pay attention to it when
> > > > > > implementing
> > > > > > > > it
> > > > > > > > >> .If
> > > > > > > > >> > > > some
> > > > > > > > >> > > > > > > > Pattern
> > > > > > > > >> > > > > > > > > has been removed or updated, will the
> > > partially
> > > > > > > matched
> > > > > > > > >> results
> > > > > > > > >> > > > in
> > > > > > > > >> > > > > > > > > StateBackend would be clean up or We rely
> on
> > > > state
> > > > > > ttl
> > > > > > > > to
> > > > > > > > >> clean
> > > > > > > > >> > > > up
> > > > > > > > >> > > > > > these
> > > > > > > > >> > > > > > > > > expired states.
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > If certain Pattern has been removed or
> > > updated,
> > > > > the
> > > > > > > > >> partially
> > > > > > > > >> > > > > matched
> > > > > > > > >> > > > > > > > > results in StateBackend would be clean up
> > > until
> > > > > the
> > > > > > > next
> > > > > > > > >> > > > > checkpoint.
> > > > > > > > >> > > > > > The
> > > > > > > > >> > > > > > > > > partially matched result doesn't depend on
> > the
> > > > > state
> > > > > > > ttl
> > > > > > > > >> of the
> > > > > > > > >> > > > > > > > > StateBackend.
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > 4. Will the PatternProcessorManager keep
> all
> > > the
> > > > > > > active
> > > > > > > > >> > > > > > PatternProcessor
> > > > > > > > >> > > > > > > > > in memory? We have also Support Multiple
> > Rule
> > > > and
> > > > > > > > Dynamic
> > > > > > > > >> Rule
> > > > > > > > >> > > > > > Changing.
> > > > > > > > >> > > > > > > > > But we are facing such a problem, some
> > users’
> > > > > usage
> > > > > > > > >> scenarios
> > > > > > > > >> > > are
> > > > > > > > >> > > > > > that
> > > > > > > > >> > > > > > > > they
> > > > > > > > >> > > > > > > > > want to have their own pattern for each
> > > user_id,
> > > > > > which
> > > > > > > > >> means
> > > > > > > > >> > > that
> > > > > > > > >> > > > > > there
> > > > > > > > >> > > > > > > > > could be thousands of patterns, which
> would
> > > make
> > > > > the
> > > > > > > > >> > > performance
> > > > > > > > >> > > > of
> > > > > > > > >> > > > > > > > Pattern
> > > > > > > > >> > > > > > > > > Matching very poor. We are also trying to
> > > solve
> > > > > this
> > > > > > > > >> problem.
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > The PatternProcessorManager keeps all the
> > > active
> > > > > > > > >> > > PatternProcessor
> > > > > > > > >> > > > > in
> > > > > > > > >> > > > > > > > > memory. For scenarios that they want to
> have
> > > > their
> > > > > > own
> > > > > > > > >> pattern
> > > > > > > > >> > > > for
> > > > > > > > >> > > > > > each
> > > > > > > > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> > > > > > > fine-grained
> > > > > > > > >> pattern
> > > > > > > > >> > > > of
> > > > > > > > >> > > > > > > > > PatternProcessor to solve the performance
> > > > problem
> > > > > of
> > > > > > > the
> > > > > > > > >> > > Pattern
> > > > > > > > >> > > > > > > > Matching,
> > > > > > > > >> > > > > > > > > for example, a pattern corresponds to a
> > group
> > > of
> > > > > > > users?
> > > > > > > > >> The
> > > > > > > > >> > > > > scenarios
> > > > > > > > >> > > > > > > > > mentioned above need to be solved by case
> by
> > > > case.
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > Best,
> > > > > > > > >> > > > > > > > > Nicholas Jiang
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > > > > > > >> > > > > > > > > > Glad to see the Community's progress in
> > > Flink
> > > > > CEP.
> > > > > > > > After
> > > > > > > > >> > > > reading
> > > > > > > > >> > > > > > this
> > > > > > > > >> > > > > > > > > Flip,
> > > > > > > > >> > > > > > > > > > I have few questions, would you please
> > take
> > > a
> > > > > look
> > > > > > > ?
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > > > > > > >> > > > PatternProcessoerDiscoverer
> > > > > > > > >> > > > > to
> > > > > > > > >> > > > > > > > > update
> > > > > > > > >> > > > > > > > > > the rules, will it increase the load of
> > JM?
> > > > For
> > > > > > > > >> example, if
> > > > > > > > >> > > the
> > > > > > > > >> > > > > > user
> > > > > > > > >> > > > > > > > > wants
> > > > > > > > >> > > > > > > > > > the updated rule to take effect
> > > immediately,,
> > > > > > which
> > > > > > > > >> means
> > > > > > > > >> > > that
> > > > > > > > >> > > > we
> > > > > > > > >> > > > > > need
> > > > > > > > >> > > > > > > > to
> > > > > > > > >> > > > > > > > > > set a shorter check interval or there
> is
> > > > > another
> > > > > > > > >> scenario
> > > > > > > > >> > > when
> > > > > > > > >> > > > > > users
> > > > > > > > >> > > > > > > > > > rarely update the pattern, will the
> > > > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > > > >> > > > > be
> > > > > > > > >> > > > > > in
> > > > > > > > >> > > > > > > > > most
> > > > > > > > >> > > > > > > > > > of the time Do useless checks ? Will a
> > lazy
> > > > > update
> > > > > > > > mode
> > > > > > > > >> could
> > > > > > > > >> > > > be
> > > > > > > > >> > > > > > used,
> > > > > > > > >> > > > > > > > > > which the pattern only be updated when
> > > > triggered
> > > > > > by
> > > > > > > > the
> > > > > > > > >> user,
> > > > > > > > >> > > > and
> > > > > > > > >> > > > > > do
> > > > > > > > >> > > > > > > > > > nothing at other times ?
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > > > 2. I still have some confusion about
> how
> > > Key
> > > > > > > > >> Generating
> > > > > > > > >> > > > > > Opertator and
> > > > > > > > >> > > > > > > > > > CepOperator (Pattern Matching &
> Processing
> > > > > > Operator)
> > > > > > > > >> work
> > > > > > > > >> > > > > > together. If
> > > > > > > > >> > > > > > > > > > there are N PatternProcessors, will the
> > Key
> > > > > > > Generating
> > > > > > > > >> > > > Opertator
> > > > > > > > >> > > > > > > > > generate N
> > > > > > > > >> > > > > > > > > > keyedStreams, and then N CepOperator
> would
> > > > > process
> > > > > > > > each
> > > > > > > > >> Key
> > > > > > > > >> > > > > > separately
> > > > > > > > >> > > > > > > > ?
> > > > > > > > >> > > > > > > > > Or
> > > > > > > > >> > > > > > > > > > every CepOperator Task would process all
> > > > > patterns,
> > > > > > > if
> > > > > > > > >> so,
> > > > > > > > >> > > does
> > > > > > > > >> > > > > the
> > > > > > > > >> > > > > > key
> > > > > > > > >> > > > > > > > > type
> > > > > > > > >> > > > > > > > > > in each PatternProcessor need to be the
> > > same ?
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > > > 3. Maybe need to pay attention to it
> when
> > > > > > > implementing
> > > > > > > > >> it .If
> > > > > > > > >> > > > > some
> > > > > > > > >> > > > > > > > > Pattern
> > > > > > > > >> > > > > > > > > > has been removed or updateed ,will the
> > > > > partially
> > > > > > > > >> matched
> > > > > > > > >> > > > results
> > > > > > > > >> > > > > > in
> > > > > > > > >> > > > > > > > > > StateBackend would be clean up or We
> rely
> > on
> > > > > state
> > > > > > > ttl
> > > > > > > > >> to
> > > > > > > > >> > > clean
> > > > > > > > >> > > > > up
> > > > > > > > >> > > > > > > > these
> > > > > > > > >> > > > > > > > > > expired states.
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > > > 4. Will the PatternProcessorManager keep
> > all
> > > > the
> > > > > > > > active
> > > > > > > > >> > > > > > > > PatternProcessor
> > > > > > > > >> > > > > > > > > in
> > > > > > > > >> > > > > > > > > > memory ? We have also Support Multiple
> > Rule
> > > > and
> > > > > > > > Dynamic
> > > > > > > > >> Rule
> > > > > > > > >> > > > > > Changing .
> > > > > > > > >> > > > > > > > > > But we are facing such a problem, some
> > > users’
> > > > > > usage
> > > > > > > > >> scenarios
> > > > > > > > >> > > > are
> > > > > > > > >> > > > > > that
> > > > > > > > >> > > > > > > > > they
> > > > > > > > >> > > > > > > > > > want to have their own pattern for each
> > > > user_id,
> > > > > > > which
> > > > > > > > >> means
> > > > > > > > >> > > > that
> > > > > > > > >> > > > > > there
> > > > > > > > >> > > > > > > > > > could be thousands of patterns, which
> > would
> > > > make
> > > > > > the
> > > > > > > > >> > > > performance
> > > > > > > > >> > > > > of
> > > > > > > > >> > > > > > > > > Pattern
> > > > > > > > >> > > > > > > > > > Matching very poor. We are also trying
> to
> > > > solve
> > > > > > this
> > > > > > > > >> problem.
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > > > Yunfeng Zhou <
> flink.zhouyunfeng@gmail.com
> > >
> > > > > > > > >> 于2021年12月10日周五
> > > > > > > > >> > > > > 19:16写道：
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > Hi all，
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > I'm opening this thread to propose the
> > > > design
> > > > > to
> > > > > > > > >> support
> > > > > > > > >> > > > > multiple
> > > > > > > > >> > > > > > > > rule
> > > > > > > > >> > > > > > > > > &
> > > > > > > > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP
> > > > > project,
> > > > > > as
> > > > > > > > >> > > described
> > > > > > > > >> > > > in
> > > > > > > > >> > > > > > > > > FLIP-200
> > > > > > > > >> > > > > > > > > > > [1]
> > > > > > > > >> > > > > > > > > > > .
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > Currently Flink CEP only supports
> > having a
> > > > > > single
> > > > > > > > >> pattern
> > > > > > > > >> > > > > inside
> > > > > > > > >> > > > > > a
> > > > > > > > >> > > > > > > > > > > CepOperator and does not support
> > changing
> > > > the
> > > > > > > > pattern
> > > > > > > > >> > > > > > dynamically. In
> > > > > > > > >> > > > > > > > > order
> > > > > > > > >> > > > > > > > > > > to reduce resource consumption and to
> > > > > experience
> > > > > > > > >> shorter
> > > > > > > > >> > > > > downtime
> > > > > > > > >> > > > > > > > > during
> > > > > > > > >> > > > > > > > > > > pattern updates, there is a growing
> need
> > > in
> > > > > the
> > > > > > > > >> production
> > > > > > > > >> > > > > > > > environment
> > > > > > > > >> > > > > > > > > that
> > > > > > > > >> > > > > > > > > > > expects CEP to support having multiple
> > > > > patterns
> > > > > > in
> > > > > > > > one
> > > > > > > > >> > > > operator
> > > > > > > > >> > > > > > and
> > > > > > > > >> > > > > > > > to
> > > > > > > > >> > > > > > > > > > > support dynamically changing them.
> > > > Therefore I
> > > > > > > > >> propose to
> > > > > > > > >> > > add
> > > > > > > > >> > > > > > certain
> > > > > > > > >> > > > > > > > > > > infrastructure as described in
> FLIP-200
> > to
> > > > > > support
> > > > > > > > >> these
> > > > > > > > >> > > > > > > > > functionalities.
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > Please feel free to reply to this
> email
> > > > > thread.
> > > > > > > > >> Looking
> > > > > > > > >> > > > forward
> > > > > > > > >> > > > > > to
> > > > > > > > >> > > > > > > > your
> > > > > > > > >> > > > > > > > > > > feedback!
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > [1]
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > >
> > > > > > > > >> > > >
> > > > > > > > >> > >
> > > > > > > > >>
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > Best regards,
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > > > Yunfeng
> > > > > > > > >> > > > > > > > > > >
> > > > > > > > >> > > > > > > > > >
> > > > > > > > >> > > > > > > > >
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > --
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > Konstantin Knauf
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > https://twitter.com/snntrable
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > > > https://github.com/knaufk
> > > > > > > > >> > > > > > > >
> > > > > > > > >> > > > > > >
> > > > > > > > >> > > > > >
> > > > > > > > >> > > > >
> > > > > > > > >> > > >
> > > > > > > > >> > >
> > > > > > > > >> > >
> > > > > > > > >> > > --
> > > > > > > > >> > >
> > > > > > > > >> > > Konstantin Knauf
> > > > > > > > >> > >
> > > > > > > > >> > > https://twitter.com/snntrable
> > > > > > > > >> > >
> > > > > > > > >> > > https://github.com/knaufk
> > > > > > > > >> > >
> > > > > > > > >> >
> > > > > > > > >>
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Becket Qin <be...@gmail.com>.
Thanks for the explanation, Till. I like the idea, but have a question
about the first step.
After the first step, would users be able to actually use the dynamic
patterns in CEP?
In the first step you mentioned, the commands and formats for a new CEP
pattern seem related to how users would ingest the commands. If we go with
the OC, these commands and formats would become internal interfaces. The
end users would just use the REST API, or in the beginning, implement a
Java plugin of dynamic pattern provider. In this case our focus would be on
designing a good plugin interface. On the other hand, if we go with the
side-input, users would need to know the command format so they can send
the commands to the CEP operator. Therefore we need to think about stuff
like versioning, request validation and backwards compatibility.
Also, because the public interface is all about how the users can ingest
the dynamic patterns. It seems we still need to figure that out before we
can conclude the FLIP.
Assuming the first step closes this FLIP and after that users would be able
to use the CEP dynamic pattern, are you suggesting the following?
1. We will design the commands and format of CEP dynamic pattern, and also
how CEP operators take them into effect. This design would assume that
users can send the commands directly to the CEP operator via side-input. So
the protocol would take versioning and format evolution into account. After
the first step, the users CAN make dynamic pattern work with the help from
some external dependencies and maintenance effort.
2. Discuss about a control plane from the use case of CEP dynamic pattern,
and let CEP dynamic pattern use that control plane if we eventually think
that is the right way to go.
Assuming that we are not going to stop after step 1 is done, will the end
state be that the CEP dynamic pattern supports both approaches? It is not
clear to me how this would work. For example, will a pattern ingested from
side-input be managed by OC as well? If more and more users pick the more
ergonomic way, would the side-input option just die out? In that case, will
we deprecate that?
My main concern is that the time and work we invest in step 1 will be
thrown away. Not only that, at the end of step 1, in order to actually use
the feature and make it production ready, there is a lot of work for the
users to do. All that work may also become in vain. So it would be good if
we can avoid that by having a clean approach to begin with. What do you
think?
Thanks,
Jiangjie (Becket) Qin
On Wed, Jan 5, 2022 at 11:35 PM Till Rohrmann <tr...@apache.org> wrote:
> I think I would scope the effort slightly differently. Note that I might be
> missing some requirements or overlook something.
>
> 1. Enable Flink to support CEP dynamic patterns
>
> Here I would define the commands and formats for a new CEP pattern. Then I
> would extend the CEP operator to understand these commands so that we can
> change the CEP patterns dynamically. This should give the building blocks
> to set up a job where you can change the CEP patterns by reading from an
> arbitrary side input the CEP pattern commands. Note that it will be the
> responsibility of the user to ingest the data somehow. This is nothing
> Flink is concerned with at this time.
>
> 2. Think about how to make the CEP dynamic pattern feature more ergonomic
>
> Here we can pick up the discussion about OC and having a REST ingestion
> endpoint in Flink vs. offering tools that live outside of Flink itself. I
> could imagine that this could become a separate small project that builds
> upon Flink, for example.
>
> Cheers,
> Till
>
> On Wed, Jan 5, 2022 at 2:19 PM Becket Qin <be...@gmail.com> wrote:
>
> > Hi Till,
> >
> > Thanks for the prompt reply. Like you said, we are indeed using the
> dynamic
> > CEP pattern use case to test the existing primitives in Flink to see if
> > they can meet the requirements. I fully understand the concern of
> > exposing OC as a user interface. Meanwhile I see CEP dynamic patterns as
> a
> > good opportunity to battle test and enhance the OC as a user facing
> control
> > plane which is currently missing. After all, there is no better person
> than
> > ourselves to try it out first.
> >
> > It is not clear to me whether it is worth continuing the effort of
> > supporting dynamic CEP pattern without concluding the control plane
> > discussion. Let's say we have a CEP job reading from Kafka. To make this
> > work with side-input, a few things need to be done.
> >
> > 1. In order to support dynamic patterns, users would create another
> > Kafka topic as side-input to receive dynamic patterns.
> > 2. In order to insert dynamic patterns, users would use a separate web
> > server that is provided by us as a separate tool. The web server takes
> > http
> > requests and sends dynamic pattern records to Kafka via a Kafka sink
> > (using
> > a KafkaProducer is likely simpler here, though).
> > 3. Regarding querying the running dynamic patterns, given Kafka is not
> > queryable, users would probably introduce a database and insert the
> > patterns there so they can query the running patterns. Maybe this
> could
> > be
> > done by the CEP operator side-output, so there is less chance of
> > inconsistency between Kafka and the database.
> > 4. If the Flink job is to be stopped, the dynamic pattern Kafka topic
> > needs to be deleted, the companion web server also needs to be stopped
> > (assuming it is not shared with other CEP jobs), and the database
> table
> > storing the dynamic pattern needs to be dropped.
> >
> > Please correct me if I misunderstood something, but this seems quite
> > involved. Moreover, all the work here is going to be thrown away after we
> > have OC as a decent user facing control plane in place. And we will
> likely
> > have a backwards incompatible API change here. Given that, I am wondering
> > if we should wait until the OC discussion concludes before moving on with
> > the dynamic patterns?
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> >
> >
> > On Wed, Jan 5, 2022 at 5:53 PM Till Rohrmann <tr...@apache.org>
> wrote:
> >
> > > Thanks for the detailed explanation Becket.
> > >
> > > Do you think that an additional dependency is a deal breaker for people
> > to
> > > use dynamic CEP patterns? At the very least people have to operate some
> > > kind of storage/queue system from which the CEP job can read anyway.
> > Maybe
> > > it could be good enough to provide a REST endpoint (as a separate tool)
> > > that can be instantiated with a Flink sink to ingest REST requests
> > > into some queue. A general concern I have is that by making the JM a
> REST
> > > ingestion point for data will push another responsibility to Flink and
> > > increase the surface area further.
> > >
> > > For how to handle data that cannot be processed by patterns, I think
> > there
> > > also exist other solutions. I could imagine that users could define
> > > different failover strategies. E.g. one could simply ignore the record,
> > the
> > > pattern could get deactivated on the affected TM or the processing
> fails.
> > >
> > > Maybe we are coupling the dynamic CEP pattern effort too much on where
> > the
> > > new patterns come from. Maybe we can split these efforts into
> supporting
> > > dynamic CEP patterns on the TM reading from some source and then fork
> off
> > > the discussion about introducing a user controlled control plane to
> > Flink.
> > > That way we wouldn't block this effort and could discuss more about the
> > > exact properties such a user control plane would need to have. What do
> > you
> > > think?
> > >
> > > Cheers,
> > > Till
> > >
> > > On Wed, Jan 5, 2022 at 7:18 AM Becket Qin <be...@gmail.com>
> wrote:
> > >
> > > > Hi Till,
> > > >
> > > > Thanks for the comments and questions. To be clear, I am not saying
> > that
> > > > the side-input stream does not work for the dynamic pattern update
> use
> > > > case. But I think OC is a better solution. The design goal for CEP
> > > dynamic
> > > > pattern is not only make it work, but also make it user friendly and
> > > > extensible. So as a user, I expect the following:
> > > >
> > > > - Use CEP with dynamic pattern update without depending on external
> > > > systems. e.g. updating the pattern by directly talking to the Flink
> job
> > > > itself.
> > > > - Some sort of isolation between patterns. e.g. a pattern update
> > failure
> > > > won't cause other running patterns to fail.
> > > > - Easy to query the currently running patterns in the Flink job.
> > > > - Extensible to add new features. e.g. apply some pattern to a subset
> > of
> > > > subtasks. Disable dynamic pattern update during a service window,
> etc.
> > > >
> > > > It looks to me that OC is a more promising way to to achieve the
> above.
> > > >
> > > > Please also see the reply to your questions inline below.
> > > >
> > > > > You mentioned that a TM might find out that a pattern is invalid
> and
> > > then
> > > > > it could use the 2-way communication with the JM to tell the other
> > TMs
> > > > that
> > > > > the pattern is invalid. How exactly would a TM detect that a
> pattern
> > is
> > > > > invalid at data processing time? And assuming that this is possible
> > > for a
> > > > > single TM, why can't the other TMs not detect this problem? Is it
> > > because
> > > > > the validity of patterns might depend on data that is different
> > between
> > > > > TMs?
> > > >
> > > >
> > > > Yes, the TMs are processing different records, so some may encounter
> > > issue
> > > > while others are running fine, for example, a field may be missing
> > from a
> > > > record while the pattern requires it. Even if all the TMs have
> detected
> > > the
> > > > problem, without a channel to report back the issue, the only thing
> TMs
> > > can
> > > > do is either to throw exception and stop processing.
> > > >
> > > > You also mentioned that deep-learning-on-flink could benefit from an
> OC
> > > > > control plane but I couldn't find the referenced link. Would
> > > > > deep-learning-on-flink like to use OCs as a kind of parameter
> server?
> > > > Could
> > > > > you elaborate on deep-learning-on-flink's usage of such a feature?
> > > >
> > > >
> > > > deep-learning-on-flink[1] has a general ML cluster abstraction that
> can
> > > run
> > > > TF / PyTorch etc. This cluster has a ML master role to manage the
> > > > liveliness of all the ML workers which are python processes running
> > > > side-by-side with TMs. The ML workers can be PS or Worker of
> > TensorFlow.
> > > > For example, if 10 TF worker and 5 TF PS nodes are needed, a Flink
> UDF
> > > > operator of parallelism 10 and a Flink Source operator with
> parallelism
> > > = 5
> > > > will be created to run the TF worker and TF PS respectively. All the
> 15
> > > > nodes running either PS or Worker are managed by the ML master. Prior
> > to
> > > > OC, the implementation was having a Source operator with parallelism
> =
> > 1
> > > to
> > > > run the master; let the ML workers register themselves to the an
> > external
> > > > ZK so the master can discover them. So basically users have to build
> > > their
> > > > own control plane. With OC, at very least, we no longer need ZK
> > anymore.
> > > >
> > > > Concerning reprocessing command history and repeatable processing
> > > results I
> > > > > think there is actually quite a big difference between using a
> Flink
> > > > source
> > > > > vs. offering a REST server that can receive command that are
> > > distributed
> > > > > via the OCs. In the former case we can rely on the external system
> to
> > > > > persist commands whereas in the latter approach we/users have to
> > > > implement
> > > > > a storage solution on their own (in the simplest case users will
> > > probably
> > > > > store everything in state which might grow indefinitely if stored
> as
> > a
> > > > > changelog).
> > > >
> > > >
> > > > It is true that a Flink Source is easier to provide a change log of
> > > > patterns. But there are also downsides. The most prominent one is
> that
> > in
> > > > order to update the dynamic pattern, users have to run an external
> > system
> > > > for the source to read. Or users have to implement a REST Source
> taking
> > > > command directly like a web server. In that case, the service
> discovery
> > > is
> > > > again a problem and needs external dependency.
> > > > On the other hand, it is not so difficult for OC to store a change
> log
> > > > history. Assuming there are 100 pattern updates / day for a CEP job
> and
> > > one
> > > > year of history should be stored. Let's say each pattern change log
> > entry
> > > > is 1K bytes. The pattern update change log for the entire year is
> just
> > 34
> > > > MB, which seems quite small. And users can also query the patterns in
> > > > effect via the same endpoint. I think this would provide a good
> > > out-of-box
> > > > experience in the vast majority of cases. No external dependencies
> and
> > a
> > > > single REST endpoint. In rare cases where there is a large amount of
> > > > pattern update log. External systems can still be leveraged. One
> > > potential
> > > > issue might be that a command that has been received but not
> > checkpointed
> > > > yet may got lost if the job fails over. This can be mitigated by
> > allowing
> > > > OC to ask JM to trigger a checkpoint (not there yet but may worth
> > > > thinking), or simply introduce a *PendingCommit* state for a pattern
> > > > indicating it's not committed yet. In the worst case, we can always
> > > > fallback to store patterns in external systems such as a database.
> > > >
> > > > Thanks,
> > > >
> > > > Jiangjie (Becket) Qin
> > > >
> > > > [1]
> > > >
> > > >
> > >
> >
> https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
> > > >
> > > >
> > > > On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <tr...@apache.org>
> > > wrote:
> > > >
> > > > > Hi Becket,
> > > > >
> > > > > Thanks for the explanation. While I do agree that a general 2-way
> > > > > communication pattern would be nice to have, I also believe that
> this
> > > > > approach is probably at least one magnitude more complex to realize
> > > than
> > > > > the side-input approach. Therefore, I really would like to
> understand
> > > why
> > > > > such a mechanism is required for the CEP use case.
> > > > >
> > > > > You mentioned that a TM might find out that a pattern is invalid
> and
> > > then
> > > > > it could use the 2-way communication with the JM to tell the other
> > TMs
> > > > that
> > > > > the pattern is invalid. How exactly would a TM detect that a
> pattern
> > is
> > > > > invalid at data processing time? And assuming that this is possible
> > > for a
> > > > > single TM, why can't the other TMs not detect this problem? Is it
> > > because
> > > > > the validity of patterns might depend on data that is different
> > between
> > > > > TMs?
> > > > >
> > > > > You also mentioned that deep-learning-on-flink could benefit from
> an
> > OC
> > > > > control plane but I couldn't find the referenced link. Would
> > > > > deep-learning-on-flink like to use OCs as a kind of parameter
> server?
> > > > Could
> > > > > you elaborate on deep-learning-on-flink's usage of such a feature?
> > > > >
> > > > > Concerning reprocessing command history and repeatable processing
> > > > results I
> > > > > think there is actually quite a big difference between using a
> Flink
> > > > source
> > > > > vs. offering a REST server that can receive command that are
> > > distributed
> > > > > via the OCs. In the former case we can rely on the external system
> to
> > > > > persist commands whereas in the latter approach we/users have to
> > > > implement
> > > > > a storage solution on their own (in the simplest case users will
> > > probably
> > > > > store everything in state which might grow indefinitely if stored
> as
> > a
> > > > > changelog).
> > > > >
> > > > > Cheers,
> > > > > Till
> > > > >
> > > > > On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com>
> > > wrote:
> > > > >
> > > > > > Hi David,
> > > > > >
> > > > > > Thanks for sharing your thoughts. Some quick reply to your
> > comments:
> > > > > >
> > > > > > We're still talking about the "web server based"
> > > > > > > pattern_processor_discoverer, but what about other use cases?
> One
> > > of
> > > > my
> > > > > > big
> > > > > > > concerns is that user's can not really reuse any part of the
> > Flink
> > > > > > > ecosystem to implement the discovery logic. For example if they
> > > want
> > > > to
> > > > > > > read patterns from Kafka topic, they need to roll their own
> > > > discoverer
> > > > > > > based on the vanilla Kafka client. If we're talking about
> > > > > extensibility,
> > > > > > > should we also make sure that the existing primitives can be
> > > reused?
> > > > > >
> > > > > >
> > > > > > KafkaSource is actually more complicated than vanilla
> KafkaConsumer
> > > > from
> > > > > > the perspective of consuming Kafka messages. The KafkaSource just
> > > helps
> > > > > > make it easier for Flink jobs to process these messages. In fact,
> > > > > > KafkaConsumer is more powerful than KafkaSource in terms of
> talking
> > > to
> > > > > > Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator]
> > and
> > > > > > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> > > > > >
> > > > > > This can be done for the side-input as well by filtering invalid
> > > > patterns
> > > > > > > before the broadcast. You can also send the invalid patterns to
> > any
> > > > > side
> > > > > > > output you want. I have a feeling that we're way too attached
> to
> > > the
> > > > > REST
> > > > > > > server use case in this discussion. I agree that for that case,
> > > this
> > > > > > > solution is the most straightforward one.
> > > > > >
> > > > > >
> > > > > > Depending on whether the invalidity is discovered in pattern
> > > definition
> > > > > > time or data processing time. e.g. A valid pattern with invalid
> > data
> > > > > which
> > > > > > fails to process can only be detected in data processing time. So
> > the
> > > > > > pattern won't be filtered out before the broadcast.
> > > > > >
> > > > > > I agree that 2-way communication in the "data-flow like" API is
> > > tricky,
> > > > > > > because it requires cycles / iterations, which are still not
> > really
> > > > > > solved
> > > > > > > (for a good reason, it's really tough nut to crack). This makes
> > me
> > > > > think
> > > > > > > that the OC may be bit of a "incomplete" workaround for not
> > having
> > > > > fully
> > > > > > > working support for iterations.
> > > > > >
> > > > > >
> > > > > > For example I'm not really confident that the checkpointing of
> the
> > OC
> > > > > works
> > > > > > > correctly right now, because it doesn't seem to require
> > checkpoint
> > > > > > barrier
> > > > > > > alignment as the regular stream inputs. We also don't have a
> > proper
> > > > > > support
> > > > > > > for watermarking (this is again tricky, because of the cycle).
> > > > > >
> > > > > >
> > > > > > If we decide to go down this road, should we first address some
> of
> > > > these
> > > > > > > limitations?
> > > > > >
> > > > > > I agree. OC is proven to be useful and we should think about how
> to
> > > > > enhance
> > > > > > it instead of not using it.
> > > > > >
> > > > > > If I understand that correctly, this means only the LATEST state
> of
> > > the
> > > > > > > patterns (in other words - patterns that are currently in use).
> > Is
> > > > this
> > > > > > > really sufficient for historical re-processing? Can someone for
> > > > example
> > > > > > > want re-process the data in more of a "temporal join" fashion?
> > Also
> > > > > AFAIK
> > > > > > > historical processing in combination with "coordinator
> > checkpoints"
> > > > is
> > > > > > not
> > > > > > > really something that we currently support of the box, are
> there
> > > any
> > > > > > plans
> > > > > > > on tackling this (my other concern is that this should not go
> > > against
> > > > > the
> > > > > > > "unified batch & stream processing" efforts)?
> > > > > >
> > > > > > I think in this case, the state would contain the entire pattern
> > > update
> > > > > > history. Not the final state, but the change log. In fact, it is
> > not
> > > > > > possible to guarantee the correct result unless you have the
> entire
> > > > > change
> > > > > > log. Even with side-input, there still could be late arrivals in
> > the
> > > > > > pattern update stream, and the only way to correct it is to
> either
> > > have
> > > > > all
> > > > > > the data reprocessed (with all the pattern change log loaded
> > upfront)
> > > > or
> > > > > > having retraction support.
> > > > > >
> > > > > > I can imagine that if this should be a concern, we could move the
> > > > > execution
> > > > > > > of the OC to the task managers. This also makes me thing, that
> we
> > > > > > shouldn't
> > > > > > > make any strong assumptions that the OC will always run in the
> > > > > JobManager
> > > > > > > (this is especially relevant for the embedded web-server use
> > case).
> > > > > >
> > > > > > This is a very good point. I think we should do this. The reason
> OC
> > > is
> > > > in
> > > > > > JM is based on the assumption that control plane usually have
> > little
> > > > > > traffic. But if that is not the case, we should move the OC out
> of
> > > JM,
> > > > > > maybe to TM.
> > > > > >
> > > > > >
> > > > > >
> > > > > > I think the key topic we are discussing is what the Flink control
> > > plane
> > > > > > should look like, and CEP is just an example use case. There are
> > > > > basically
> > > > > > two options:
> > > > > >
> > > > > > 1. Using the side-input / broadcast stream
> > > > > > 2. Using the OperatorCoordinator.
> > > > > >
> > > > > > Although we are having this discussion under the context of
> > > supporting
> > > > > CEP
> > > > > > dynamic pattern update, it would be really helpful to reach
> > agreement
> > > > on
> > > > > > the design principle in general of how Flink should handle
> similar
> > > > > external
> > > > > > control demands, a.k.a how to provide a decent control plane in
> > Flink
> > > > to
> > > > > > the users.
> > > > > >
> > > > > > Here is my take on these two options, based on the requirements
> of
> > a
> > > > > > control plane.
> > > > > >
> > > > > > *Communication Requirements*
> > > > > > Flink has two kinds of control planes - in-band and out-of-band.
> > > > > > In-band control plane is like watermark and checkpoint marker. It
> > > > > requires
> > > > > > the entire DAG to be in a consistent state, so the control
> messages
> > > > flow
> > > > > > with the data in one direction. This is a one-way control flow.
> > > > > > Examples of out-of-band control plane is OC and JM/TM
> > communication.
> > > > They
> > > > > > do not require a global consistency or awareness across the
> entire
> > > DAG.
> > > > > >
> > > > > > Before OC, neither of these two kinds of control plain was
> exposed
> > to
> > > > the
> > > > > > users. OC allows the users to leverage the out-of-band control
> > plane
> > > so
> > > > > > they can coordinate across subtasks. This is a more widely used
> > > control
> > > > > > flow from user defined operator perspective which requires 2-way
> > > > > > communication.
> > > > > >
> > > > > > - side-input stream is one-way communication. Moreover, I
> don't
> > > > think
> > > > > > iteration is the right way to address this. Unlike the
> > abstraction
> > > > of
> > > > > > data
> > > > > > processing which is a DAG, the control plane may require
> > > > communication
> > > > > > between arbitrary two operators in different orders. Using
> > > > iterations
> > > > > > may
> > > > > > end up with an explosion of feedback edges that are not only
> > > > > > complicated to
> > > > > > express, but also hard to debug and maintain.
> > > > > > - OC provides a decent 2-way communication mechanism.
> > > > > >
> > > > > >
> > > > > > *Cost for low traffic use case*
> > > > > > An important difference between data channel and control channel
> is
> > > > > traffic
> > > > > > pattern. Unlike data plane, the control plane is usually idle for
> > the
> > > > > vast
> > > > > > majority of the time with occasional control messages.
> > > > > >
> > > > > > - One argument to use the side-input / broadcast stream was
> that
> > > > users
> > > > > > can reuse the existing connectors. However, most Flink sources
> > are
> > > > > > designed
> > > > > > to handle large throughput of traffic that maintains all the
> > > > threads,
> > > > > > network connections, etc. Not to say the external resources
> such
> > > as
> > > > > > Kafka
> > > > > > topics to store the commands.
> > > > > > - OC can have a much lower constant cost.
> > > > > >
> > > > > >
> > > > > > *Easy to use*
> > > > > > Personally speaking, I think the most simple and user-friendly
> > > > interface
> > > > > is
> > > > > > a REST API that accepts control commands.
> > > > > >
> > > > > > - One proposal at this point is to have a separate web server
> > > > > > independent of the Flink job. In that case, should users
> > implement
> > > > > that
> > > > > > web
> > > > > > server? In order to pass the command to the Flink job, does
> that
> > > > mean
> > > > > > users
> > > > > > should implement a Flink source that can read the commands
> from
> > > the
> > > > > web
> > > > > > server? Or the web server would send the command to something
> > like
> > > > > Kafka
> > > > > > and let the Flink side-input read from there. There seems to
> be
> > a
> > > > lot
> > > > > > for
> > > > > > the users to do. And it seems an unnecessarily complicated
> > system
> > > to
> > > > > > build
> > > > > > to send occasional control messages to a Flink job.
> > > > > > - OC can simply be reached via the JM REST API.
> > > > > > - e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > > > > > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx>
> would
> > > > simply
> > > > > > send the Content to the OC of OP_NAME.
> > > > > >
> > > > > > *Work well with checkpoints*
> > > > > >
> > > > > > - side-input streams works well with checkpoint, thanks to its
> > > > > > compatibility to the DAG abstraction.
> > > > > > - The OperatorCoordinator requires more careful design to work
> > > well
> > > > > with
> > > > > > checkpoints. The complexity mostly comes from the 2-way
> > > > communication.
> > > > > > At
> > > > > > this point the OperatorCoordinator message delivery semantic
> may
> > > not
> > > > > be
> > > > > > as
> > > > > > robust as side-input streams. However, I think this is mainly
> > due
> > > to
> > > > > > potential bugs in implementation instead of fundamental design
> > > > > problems.
> > > > > > Basically the checkpoint semantic should be:
> > > > > > - The JM will first checkpoint all the OperatorCoordinator,
> > > more
> > > > > > specifically for each OperatorCoordinator,
> > > > > > - 1) JM blocks the input queue to stop receiving new
> > events
> > > > from
> > > > > > the subtasks.
> > > > > > - 2) let all the operator coordinator finish processing
> > all
> > > > the
> > > > > > pending events in the OC input queue.
> > > > > > - 3) flush the OC output queue until all the events sent
> > are
> > > > > > acknowledged.
> > > > > > - 3) unblock the input queue, but block the output queue
> > > until
> > > > > all
> > > > > > the subtasks of the OC finish checkpoints.
> > > > > > - The JM starts a normal checkpoint starting from the
> Source.
> > > > > > - If an operator has a coordinator, and it has sent some
> > > > events
> > > > > to
> > > > > > the OC but has not been acknowledged. These events need
> to
> > > be
> > > > > > put into the
> > > > > > subtasks' checkpoint.
> > > > > > - After all the subtasks of an operator finishes
> checkpoint,
> > > the
> > > > > > output queue of the corresponding OC can be unblocked.
> > > > > > It looks that the above protocol would let OC have a clear
> > > > checkpoint
> > > > > > semantic. And this complexity seems must for 2-way
> > communication.
> > > I
> > > > > > think
> > > > > > we are able to hide the above protocol from users by having an
> > > > > abstract
> > > > > > OC
> > > > > > implementation.
> > > > > >
> > > > > >
> > > > > > *Reprocess command history and repeatable processing results*
> > > > > > This seems not something generally required for a control plane.
> > But
> > > if
> > > > > the
> > > > > > control plane changes the data processing behavior, there might
> be
> > > some
> > > > > use
> > > > > > case. Just like the CEP pattern update. In order to do this,
> users
> > > will
> > > > > > need to provide a full command history to the operators. That
> > > consists
> > > > of
> > > > > > two steps:
> > > > > >
> > > > > > 1. get the full command history. (Flink Source V.S. Custom
> way
> > to
> > > > > > retrieve command history.)
> > > > > > 2. send them to the operators. (Side-input V.S. OC/Operator
> > > > > > communication)l
> > > > > >
> > > > > > I actually don't feel much difference between these two options.
> I
> > am
> > > > not
> > > > > > sure if a Flink source is necessarily simpler than the user
> > > implemented
> > > > > > logic. For example, if all the changes are just written in a
> > database
> > > > > > table. From the user's perspective, I feel fine with querying the
> > DB
> > > by
> > > > > > myself using something like JDBC (or use KafkaConsumer to read
> the
> > > > > pattern
> > > > > > history from a Kafka topic) and send all the pattern change
> history
> > > to
> > > > > the
> > > > > > operators before they start to process the actual events.
> > > > > >
> > > > > > *Stability impact to the Flink Job*
> > > > > > I agree this is a valid concern. There is only one JM and
> currently
> > > OC
> > > > > runs
> > > > > > there, which may potentially cause JM crash and result in job
> > > failure.
> > > > > > Running in TM may have a less impact. So I think it makes sense
> to
> > > run
> > > > OC
> > > > > > in TM. However, this is more of how we can implement OC to make
> it
> > > more
> > > > > > robust. It does not forfeit the other semantic and user
> experience
> > > > > benefits
> > > > > > mentioned above.
> > > > > >
> > > > > >
> > > > > > To sum up:
> > > > > > 1. Regardless of whether CEP chooses OC or side-input stream, a
> > > decent
> > > > > > 2-way communication control plane seems really helpful and has
> been
> > > > > proven
> > > > > > by quite a few existing use cases. To me the question is how to
> > make
> > > it
> > > > > > more robust, not whether we should use it or not.
> > > > > > 2. As for CEP, if we assume OC will be robust enough, personally
> I
> > > feel
> > > > > OC
> > > > > > is a better fit than side-input mainly because of the simplicity
> > and
> > > > > > extensibility.
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Jiangjie (Becket) Qin
> > > > > >
> > > > > >
> > > > > > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org>
> > > wrote:
> > > > > >
> > > > > > > Hi all,
> > > > > > >
> > > > > > > sorry for the late reply, vacation season ;) I'm still not 100%
> > > sold
> > > > on
> > > > > > > choosing the OC for this use-case, but on the other hand I
> don't
> > > have
> > > > > > > strong arguments against it. Few more questions / thoughts:
> > > > > > >
> > > > > > > We're still talking about the "web server based"
> > > > > > > pattern_processor_discoverer, but what about other use cases?
> One
> > > of
> > > > my
> > > > > > big
> > > > > > > concerns is that user's can not really reuse any part of the
> > Flink
> > > > > > > ecosystem to implement the discovery logic. For example if they
> > > want
> > > > to
> > > > > > > read patterns from Kafka topic, they need to roll their own
> > > > discoverer
> > > > > > > based on the vanilla Kafka client. If we're talking about
> > > > > extensibility,
> > > > > > > should we also make sure that the existing primitives can be
> > > reused?
> > > > > > >
> > > > > > > For instance, the example I gave in my previous email seems not
> > > > easily
> > > > > > > > achievable with side-input / broadcast streams: a single
> > invalid
> > > > > > pattern
> > > > > > > > detected on a TM can be disabled elegantly globally without
> > > > crashing
> > > > > > the
> > > > > > > > entire Flink job.
> > > > > > >
> > > > > > >
> > > > > > > This can be done for the side-input as well by filtering
> invalid
> > > > > patterns
> > > > > > > before the broadcast. You can also send the invalid patterns to
> > any
> > > > > side
> > > > > > > output you want. I have a feeling that we're way too attached
> to
> > > the
> > > > > REST
> > > > > > > server use case in this discussion. I agree that for that case,
> > > this
> > > > > > > solution is the most straightforward one.
> > > > > > >
> > > > > > > OC is a 2-way communication mechanism, i.e. a subtask can also
> > send
> > > > > > > > OperatorEvent to the coordinator to report its owns status,
> so
> > > that
> > > > > the
> > > > > > > > coordinator can act accordingly.
> > > > > > > >
> > > > > > >
> > > > > > > I agree that 2-way communication in the "data-flow like" API is
> > > > tricky,
> > > > > > > because it requires cycles / iterations, which are still not
> > really
> > > > > > solved
> > > > > > > (for a good reason, it's really tough nut to crack). This makes
> > me
> > > > > think
> > > > > > > that the OC may be bit of a "incomplete" workaround for not
> > having
> > > > > fully
> > > > > > > working support for iterations.
> > > > > > >
> > > > > > > For example I'm not really confident that the checkpointing of
> > the
> > > OC
> > > > > > works
> > > > > > > correctly right now, because it doesn't seem to require
> > checkpoint
> > > > > > barrier
> > > > > > > alignment as the regular stream inputs. We also don't have a
> > proper
> > > > > > support
> > > > > > > for watermarking (this is again tricky, because of the cycle).
> > > > > > >
> > > > > > > If we decide to go down this road, should we first address some
> > of
> > > > > these
> > > > > > > limitations?
> > > > > > >
> > > > > > > OperatorCoordinator will checkpoint the full amount of
> > > > PatternProcessor
> > > > > > > > data. For the reprocessing of historical data, you can read
> the
> > > > > > > > PatternProcessor snapshots saved by this checkpoint from a
> > > certain
> > > > > > > > historical checkpoint, and then recreate the historical data
> > > > through
> > > > > > > these
> > > > > > > > PatternProcessor snapshots.
> > > > > > > >
> > > > > > >
> > > > > > > If I understand that correctly, this means only the LATEST
> state
> > of
> > > > the
> > > > > > > patterns (in other words - patterns that are currently in use).
> > Is
> > > > this
> > > > > > > really sufficient for historical re-processing? Can someone for
> > > > example
> > > > > > > want re-process the data in more of a "temporal join" fashion?
> > Also
> > > > > AFAIK
> > > > > > > historical processing in combination with "coordinator
> > checkpoints"
> > > > is
> > > > > > not
> > > > > > > really something that we currently support of the box, are
> there
> > > any
> > > > > > plans
> > > > > > > on tackling this (my other concern is that this should not go
> > > against
> > > > > the
> > > > > > > "unified batch & stream processing" efforts)?
> > > > > > >
> > > > > > > I do agree that having the user defined control logic defined
> in
> > > the
> > > > JM
> > > > > > > > increases the chance of instability.
> > > > > > > >
> > > > > > >
> > > > > > > I can imagine that if this should be a concern, we could move
> the
> > > > > > execution
> > > > > > > of the OC to the task managers. This also makes me thing, that
> we
> > > > > > shouldn't
> > > > > > > make any strong assumptions that the OC will always run in the
> > > > > JobManager
> > > > > > > (this is especially relevant for the embedded web-server use
> > case).
> > > > > > >
> > > > > > > If an agreement is reached on OperatorCoodinator, I will start
> > the
> > > > > voting
> > > > > > > > thread.
> > > > > > > >
> > > > > > >
> > > > > > > As for the vote, I'd would be great if we can wait until the
> next
> > > > week
> > > > > as
> > > > > > > many people took vacation until end of the year.
> > > > > > >
> > > > > > > Overall, I really like the feature, this will be a great
> addition
> > > to
> > > > > > Flink.
> > > > > > >
> > > > > > > Best,
> > > > > > > D.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <
> > > > martijn@ververica.com
> > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > > > Hi all,
> > > > > > > >
> > > > > > > > I can understand the need for a control plane mechanism. I'm
> > not
> > > > the
> > > > > > > > technical go-to person for questions on the
> > OperatorCoordinator,
> > > > but
> > > > > I
> > > > > > > > would expect that we could offer those interfaces from Flink
> > but
> > > > > > > shouldn't
> > > > > > > > recommend running user-code in the JobManager itself. I think
> > the
> > > > > user
> > > > > > > code
> > > > > > > > (like a webserver) should run outside of Flink (like via a
> > > sidecar)
> > > > > and
> > > > > > > use
> > > > > > > > only the provided interfaces to communicate.
> > > > > > > >
> > > > > > > > I would like to get @David Morávek <dm...@apache.org> opinion
> > on
> > > > the
> > > > > > > > technical part.
> > > > > > > >
> > > > > > > > Best regards,
> > > > > > > >
> > > > > > > > Martijn
> > > > > > > >
> > > > > > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> > > > > nicholasjiang@apache.org
> > > > > > >
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > >> Hi Konstantin, Becket, Martijn,
> > > > > > > >>
> > > > > > > >> Thanks for sharing your feedback. What other concerns do you
> > > have
> > > > > > about
> > > > > > > >> OperatorCoodinator? If an agreement is reached on
> > > > > OperatorCoodinator,
> > > > > > I
> > > > > > > >> will start the voting thread.
> > > > > > > >>
> > > > > > > >> Best,
> > > > > > > >> Nicholas Jiang
> > > > > > > >>
> > > > > > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > > > > > >> > Hi Konstantin,
> > > > > > > >> >
> > > > > > > >> > Thanks for sharing your thoughts. Please see the reply
> > inline
> > > > > below.
> > > > > > > >> >
> > > > > > > >> > Thanks,
> > > > > > > >> >
> > > > > > > >> > Jiangjie (Becket) Qin
> > > > > > > >> >
> > > > > > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> > > > > knaufk@apache.org
> > > > > > >
> > > > > > > >> wrote:
> > > > > > > >> >
> > > > > > > >> > > Hi Becket, Hi Nicholas,
> > > > > > > >> > >
> > > > > > > >> > > Thanks for joining the discussion.
> > > > > > > >> > >
> > > > > > > >> > > 1 ) Personally, I would argue that we should only run
> user
> > > > code
> > > > > in
> > > > > > > the
> > > > > > > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems
> > wrong
> > > to
> > > > > me
> > > > > > to
> > > > > > > >> > > encourage users to e.g. run a webserver on the
> Jobmanager,
> > > or
> > > > > > > >> continuously
> > > > > > > >> > > read patterns from a Kafka Topic on the Jobmanager, but
> > both
> > > > of
> > > > > > > these
> > > > > > > >> I see
> > > > > > > >> > > happening with the current design. We've had lots of
> > issues
> > > > with
> > > > > > > >> > > classloading leaks and other stability issues on the
> > > > Jobmanager
> > > > > > and
> > > > > > > >> making
> > > > > > > >> > > this more complicated, if there is another way, seems
> > > > > unnecessary.
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > I think the key question here is what primitive does Flink
> > > > provide
> > > > > > to
> > > > > > > >> > facilitate the user implementation of their own control
> > logic
> > > /
> > > > > > > control
> > > > > > > >> > plane? It looks that previously, Flink assumes that all
> the
> > > user
> > > > > > logic
> > > > > > > >> is
> > > > > > > >> > just data processing logic without any control /
> > coordination
> > > > > > > >> requirements.
> > > > > > > >> > However, it turns out that a decent control plane
> > abstraction
> > > is
> > > > > > > >> required
> > > > > > > >> > in association with the data processing logic in many
> cases,
> > > > > > including
> > > > > > > >> > Source / Sink and other user defined operators in general.
> > The
> > > > > fact
> > > > > > > >> that we
> > > > > > > >> > ended up with adding the SplitEnumerator and
> GlobalCommitter
> > > are
> > > > > > just
> > > > > > > >> two
> > > > > > > >> > examples of the demand of such coordination among user
> > defined
> > > > > > logics.
> > > > > > > >> > There are other cases that we see in ecosystem projects,
> > such
> > > as
> > > > > > > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > > > > > > >> >
> > > > > > > >> > Such control plane primitives are critical to the
> > > extensibility
> > > > > of a
> > > > > > > >> > project. If we look at other projects, exposing such
> control
> > > > plane
> > > > > > > >> logic is
> > > > > > > >> > quite common. For example, Hadoop ended up with exposing
> > YARN
> > > > as a
> > > > > > > >> public
> > > > > > > >> > API to the users, which is extremely popular. Kafka
> > consumers
> > > > > > exposed
> > > > > > > >> the
> > > > > > > >> > consumer group rebalance logic to the users via
> > > > > > > >> ConsumerPartitionAssigner,
> > > > > > > >> > which is also a control plane primitive.
> > > > > > > >> >
> > > > > > > >> > To me it is more important to think about how we can
> improve
> > > the
> > > > > > > >> stability
> > > > > > > >> > of such a control plane mechanism, instead of simply
> saying
> > no
> > > > to
> > > > > > the
> > > > > > > >> users.
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > > 2) In addition, I suspect that, over time we will have
> to
> > > > > > implement
> > > > > > > >> all the
> > > > > > > >> > > functionality that regular sources already provide
> around
> > > > > > > consistency
> > > > > > > >> > > (watermarks, checkpointing) for the
> > > > PatternProcessorCoordinator,
> > > > > > > too.
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > I think OperatorCoordinator should have a generic
> > > communication
> > > > > > > >> mechanism
> > > > > > > >> > for all the operators, not specific to Source. We should
> > > > probably
> > > > > > have
> > > > > > > >> an
> > > > > > > >> > AbstractOperatorCoordinator help dealing with the
> > > communication
> > > > > > layer,
> > > > > > > >> and
> > > > > > > >> > leave the state maintenance and event handling logic to
> the
> > > user
> > > > > > code.
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > > 3) I understand that running on the Jobmanager is easier
> > if
> > > > you
> > > > > > want
> > > > > > > >> to
> > > > > > > >> > > launch a REST server directly. Here my question would
> be:
> > > does
> > > > > > this
> > > > > > > >> really
> > > > > > > >> > > need to be solved inside of Flink or couldn't you start
> a
> > > > > > webserver
> > > > > > > >> next to
> > > > > > > >> > > Flink? If we start using the Jobmanager as a REST server
> > > users
> > > > > > will
> > > > > > > >> expect
> > > > > > > >> > > that e.g. it is highly available and can be load
> balanced
> > > and
> > > > we
> > > > > > > >> quickly
> > > > > > > >> > > need to think about aspects that we never wanted to
> think
> > > > about
> > > > > in
> > > > > > > the
> > > > > > > >> > > context of a Flink Jobmanager.
> > > > > > > >> > >
> > > > > > > >> >
> > > > > > > >> > I think the REST API is just for receiving commands
> > targeting
> > > a
> > > > > > > running
> > > > > > > >> > Flink job. If the job fails, the REST API would be
> useless.
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > > So, can you elaborate a bit more, why a
> > side-input/broadcast
> > > > > > stream
> > > > > > > is
> > > > > > > >> > >
> > > > > > > >> > > a) more difficult
> > > > > > > >> > > b) has vague semantics (To me semantics of a
> stream-stream
> > > > seem
> > > > > > > >> clearer
> > > > > > > >> > > when it comes to out-of-orderness, late data,
> reprocessing
> > > or
> > > > > > batch
> > > > > > > >> > > execution mode.)
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > I do agree that having the user defined control logic
> > defined
> > > in
> > > > > the
> > > > > > > JM
> > > > > > > >> > increases the chance of instability. In that case, we may
> > > think
> > > > of
> > > > > > > other
> > > > > > > >> > solutions and I am fully open to that. But the side-input
> /
> > > > > > broadcast
> > > > > > > >> > stream seems more like a bandaid instead of a carefully
> > > designed
> > > > > > > control
> > > > > > > >> > plane mechanism.
> > > > > > > >> >
> > > > > > > >> > A decent control plane requires two-way communication, so
> > > > > > information
> > > > > > > >> can
> > > > > > > >> > be reported / collected from the entity being controlled,
> > and
> > > > the
> > > > > > > >> > coordinator / controller can send decisions or commands to
> > the
> > > > > > > entities
> > > > > > > >> > accordingly, just like our TM / JM communication. IIUC,
> this
> > > is
> > > > > not
> > > > > > > >> > achievable with the existing side-input / broadcast stream
> > as
> > > > both
> > > > > > of
> > > > > > > >> them
> > > > > > > >> > are one-way communication mechanisms. For instance, the
> > > example
> > > > I
> > > > > > gave
> > > > > > > >> in
> > > > > > > >> > my previous email seems not easily achievable with
> > side-input
> > > /
> > > > > > > >> broadcast
> > > > > > > >> > streams: a single invalid pattern detected on a TM can be
> > > > disabled
> > > > > > > >> > elegantly globally without crashing the entire Flink job.
> > > > > > > >> >
> > > > > > > >> >
> > > > > > > >> > > Cheers,
> > > > > > > >> > >
> > > > > > > >> > > Konstantin
> > > > > > > >> > >
> > > > > > > >> > >
> > > > > > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> > > > > becket.qin@gmail.com
> > > > > > >
> > > > > > > >> wrote:
> > > > > > > >> > >
> > > > > > > >> > > > Hi folks,
> > > > > > > >> > > >
> > > > > > > >> > > > I just finished reading the previous emails. It was a
> > good
> > > > > > > >> discussion.
> > > > > > > >> > > Here
> > > > > > > >> > > > are my two cents:
> > > > > > > >> > > >
> > > > > > > >> > > > *Is OperatorCoordinator a public API?*
> > > > > > > >> > > > Regarding the OperatorCoordinator, although it is
> marked
> > > as
> > > > > > > internal
> > > > > > > >> > > > interface at this point, I intended to make it a
> public
> > > > > > interface
> > > > > > > >> when
> > > > > > > >> > > add
> > > > > > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> > > > > communication
> > > > > > > >> mechanism
> > > > > > > >> > > > that enables many use cases, Source / Sink / TF on
> > Flink /
> > > > CEP
> > > > > > > here
> > > > > > > >> > > again.
> > > > > > > >> > > > To my understanding, OC was marked as internal because
> > we
> > > > > think
> > > > > > it
> > > > > > > >> is not
> > > > > > > >> > > > stable enough yet. We may need to fortify the
> > > OperatorEvent
> > > > > > > delivery
> > > > > > > >> > > > semantic a little bit so it works well with checkpoint
> > in
> > > > > > general.
> > > > > > > >> > > >
> > > > > > > >> > > > I think it is a valid concern that user code running
> in
> > JM
> > > > may
> > > > > > > cause
> > > > > > > >> > > > instability. However, not providing this communication
> > > > > mechanism
> > > > > > > >> only
> > > > > > > >> > > makes
> > > > > > > >> > > > a lot of use case even harder to implement. So it
> seems
> > > that
> > > > > > > having
> > > > > > > >> the
> > > > > > > >> > > OC
> > > > > > > >> > > > exposed to end users brings more benefits than harm to
> > > > Flink.
> > > > > At
> > > > > > > >> the end
> > > > > > > >> > > of
> > > > > > > >> > > > the day, users have many ways to crash a Flink job if
> > they
> > > > do
> > > > > > not
> > > > > > > >> write
> > > > > > > >> > > > proper code. So making those who know what they do
> happy
> > > > seems
> > > > > > > more
> > > > > > > >> > > > important here.
> > > > > > > >> > > >
> > > > > > > >> > > > *OperatorCoordinator V.S. side-input / broadcast
> stream*
> > > > > > > >> > > > I think both of them can achieve the goal of dynamic
> > > > patterns.
> > > > > > The
> > > > > > > >> main
> > > > > > > >> > > > difference is the extensibility.
> > > > > > > >> > > >
> > > > > > > >> > > > OC is a 2-way communication mechanism, i.e. a subtask
> > can
> > > > also
> > > > > > > send
> > > > > > > >> > > > OperatorEvent to the coordinator to report its owns
> > > status,
> > > > so
> > > > > > > that
> > > > > > > >> the
> > > > > > > >> > > > coordinator can act accordingly. This is sometimes
> > useful.
> > > > For
> > > > > > > >> example, a
> > > > > > > >> > > > single invalid pattern can be disabled elegantly
> without
> > > > > > crashing
> > > > > > > >> the
> > > > > > > >> > > > entire Flink job. In the future, if we allow users to
> > send
> > > > > > > external
> > > > > > > >> > > command
> > > > > > > >> > > > to OC via JM, a default self-contained implementation
> > can
> > > > just
> > > > > > > >> update the
> > > > > > > >> > > > pattern via the REST API without external
> dependencies.
> > > > > > > >> > > >
> > > > > > > >> > > > Another reason I personally prefer OC is because it is
> > an
> > > > > > explicit
> > > > > > > >> > > control
> > > > > > > >> > > > plain mechanism, where as the side-input / broadcast
> > > stream
> > > > > has
> > > > > > > are
> > > > > > > >> more
> > > > > > > >> > > > vague semantic.
> > > > > > > >> > > >
> > > > > > > >> > > > Thanks,
> > > > > > > >> > > >
> > > > > > > >> > > > Jiangjie (Becket) Qin
> > > > > > > >> > > >
> > > > > > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> > > > > dmvk@apache.org>
> > > > > > > >> wrote:
> > > > > > > >> > > >
> > > > > > > >> > > > > Hi Yunfeng,
> > > > > > > >> > > > >
> > > > > > > >> > > > > thanks for drafting this FLIP, this will be a great
> > > > addition
> > > > > > > into
> > > > > > > >> the
> > > > > > > >> > > CEP
> > > > > > > >> > > > > toolbox!
> > > > > > > >> > > > >
> > > > > > > >> > > > > Apart from running user code in JM, which want to
> > avoid
> > > in
> > > > > > > >> general, I'd
> > > > > > > >> > > > > have one more another concern about using the
> > > > > > > OperatorCoordinator
> > > > > > > >> and
> > > > > > > >> > > > that
> > > > > > > >> > > > > is re-processing of the historical data. Any
> thoughts
> > > > about
> > > > > > how
> > > > > > > >> this
> > > > > > > >> > > will
> > > > > > > >> > > > > work with the OC?
> > > > > > > >> > > > >
> > > > > > > >> > > > > I have a slight feeling that a side-input (custom
> > > source /
> > > > > > > >> operator +
> > > > > > > >> > > > > broadcast) would a better fit for this case. This
> > would
> > > > > > simplify
> > > > > > > >> the
> > > > > > > >> > > > > consistency concerns (watermarks + pushback) and the
> > > > > > > >> re-processing of
> > > > > > > >> > > > > historical data.
> > > > > > > >> > > > >
> > > > > > > >> > > > > Best,
> > > > > > > >> > > > > D.
> > > > > > > >> > > > >
> > > > > > > >> > > > >
> > > > > > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > > > > > >> > > nicholasjiang@apache.org
> > > > > > > >> > > > >
> > > > > > > >> > > > > wrote:
> > > > > > > >> > > > >
> > > > > > > >> > > > > > Hi Konstantin, Martijn
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > Thanks for the detailed feedback in the
> discussion.
> > > > What I
> > > > > > > >> still have
> > > > > > > >> > > > > left
> > > > > > > >> > > > > > to answer/reply to:
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > -- Martijn: Just to be sure, this indeed would
> mean
> > > that
> > > > > if
> > > > > > > for
> > > > > > > >> > > > whatever
> > > > > > > >> > > > > > reason the heartbeat timeout, it would crash the
> > job,
> > > > > right?
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > IMO, if for whatever reason the heartbeat timeout,
> > it
> > > > > > couldn't
> > > > > > > >> check
> > > > > > > >> > > > the
> > > > > > > >> > > > > > PatternProcessor consistency between the
> > > > > OperatorCoordinator
> > > > > > > >> and the
> > > > > > > >> > > > > > subtasks so that the job would be crashed.
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > -- Konstantin: What I was concerned about is that
> we
> > > > > > basically
> > > > > > > >> let
> > > > > > > >> > > > users
> > > > > > > >> > > > > > run a UserFunction in the OperatorCoordinator,
> which
> > > it
> > > > > does
> > > > > > > >> not seem
> > > > > > > >> > > > to
> > > > > > > >> > > > > > have been designed for.
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > In general, we have reached an agreement on the
> > design
> > > > of
> > > > > > this
> > > > > > > >> FLIP,
> > > > > > > >> > > > but
> > > > > > > >> > > > > > there are some concerns on the
> OperatorCoordinator,
> > > > about
> > > > > > > >> whether
> > > > > > > >> > > > > basically
> > > > > > > >> > > > > > let users run a UserFunction in the
> > > OperatorCoordinator
> > > > is
> > > > > > > >> designed
> > > > > > > >> > > for
> > > > > > > >> > > > > > OperatorCoordinator. We would like to invite
> Becket
> > > Qin
> > > > > who
> > > > > > is
> > > > > > > >> the
> > > > > > > >> > > > author
> > > > > > > >> > > > > > of OperatorCoordinator to help us to answer this
> > > > concern.
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > Best,
> > > > > > > >> > > > > > Nicholas Jiang
> > > > > > > >> > > > > >
> > > > > > > >> > > > > >
> > > > > > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > > > > > >> > > > > > > Hi all,
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > Really like the discussion on this topic moving
> > > > > forward. I
> > > > > > > >> really
> > > > > > > >> > > > think
> > > > > > > >> > > > > > > this feature will be much appreciated by the
> Flink
> > > > > users.
> > > > > > > >> What I
> > > > > > > >> > > > still
> > > > > > > >> > > > > > have
> > > > > > > >> > > > > > > left to answer/reply to:
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > -- Good point. If for whatever reason the
> > different
> > > > > > > >> taskmanagers
> > > > > > > >> > > > can't
> > > > > > > >> > > > > > get
> > > > > > > >> > > > > > > the latest rule, the Operator Coordinator could
> > > send a
> > > > > > > >> heartbeat to
> > > > > > > >> > > > all
> > > > > > > >> > > > > > > taskmanagers with the latest rules and check the
> > > > > heartbeat
> > > > > > > >> response
> > > > > > > >> > > > > from
> > > > > > > >> > > > > > > all the taskmanagers whether the latest rules of
> > the
> > > > > > > >> taskmanager is
> > > > > > > >> > > > > equal
> > > > > > > >> > > > > > > to these of the Operator Coordinator.
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > Just to be sure, this indeed would mean that if
> > for
> > > > > > whatever
> > > > > > > >> reason
> > > > > > > >> > > > the
> > > > > > > >> > > > > > > heartbeat timeout, it would crash the job,
> right?
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > -- We have consided about the solution mentioned
> > > > above.
> > > > > In
> > > > > > > >> this
> > > > > > > >> > > > > > solution, I
> > > > > > > >> > > > > > > have some questions about how to guarantee the
> > > > > consistency
> > > > > > > of
> > > > > > > >> the
> > > > > > > >> > > > rule
> > > > > > > >> > > > > > > between each TaskManager. By having a coodinator
> > in
> > > > the
> > > > > > > >> JobManager
> > > > > > > >> > > to
> > > > > > > >> > > > > > > centrally manage the latest rules, the latest
> > rules
> > > of
> > > > > all
> > > > > > > >> > > > TaskManagers
> > > > > > > >> > > > > > are
> > > > > > > >> > > > > > > consistent with those of the JobManager, so as
> to
> > > > avoid
> > > > > > the
> > > > > > > >> > > > > > inconsistencies
> > > > > > > >> > > > > > > that may be encountered in the above solution.
> Can
> > > you
> > > > > > > >> introduce
> > > > > > > >> > > how
> > > > > > > >> > > > > this
> > > > > > > >> > > > > > > solution guarantees the consistency of the
> rules?
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > The consistency that we could guarantee was
> based
> > on
> > > > how
> > > > > > > >> often each
> > > > > > > >> > > > > > > TaskManager would do a refresh and how often we
> > > would
> > > > > > > accept a
> > > > > > > >> > > > refresh
> > > > > > > >> > > > > to
> > > > > > > >> > > > > > > fail. We set the refresh time to a relatively
> > short
> > > > one
> > > > > > (30
> > > > > > > >> > > seconds)
> > > > > > > >> > > > > and
> > > > > > > >> > > > > > > maximum failures to 3. That meant that we could
> > > > > guarantee
> > > > > > > that
> > > > > > > >> > > rules
> > > > > > > >> > > > > > would
> > > > > > > >> > > > > > > be updated in < 2 minutes or else the job would
> > > crash.
> > > > > > That
> > > > > > > >> was
> > > > > > > >> > > > > > sufficient
> > > > > > > >> > > > > > > for our use cases. This also really depends on
> how
> > > big
> > > > > > your
> > > > > > > >> cluster
> > > > > > > >> > > > > is. I
> > > > > > > >> > > > > > > can imagine that if you have a large scale
> cluster
> > > > that
> > > > > > you
> > > > > > > >> want to
> > > > > > > >> > > > > run,
> > > > > > > >> > > > > > > you don't want to DDOS the backend system where
> > you
> > > > have
> > > > > > > your
> > > > > > > >> rules
> > > > > > > >> > > > > > stored.
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > -- In summary, the current design is that
> > JobManager
> > > > > tells
> > > > > > > all
> > > > > > > >> > > > > > TaskManagers
> > > > > > > >> > > > > > > the latest rules through OperatorCoodinator, and
> > > will
> > > > > > > >> initiate a
> > > > > > > >> > > > > > heartbeat
> > > > > > > >> > > > > > > to check whether the latest rules on each
> > > TaskManager
> > > > > are
> > > > > > > >> > > consistent.
> > > > > > > >> > > > > We
> > > > > > > >> > > > > > > will describe how to deal with the Failover
> > scenario
> > > > in
> > > > > > more
> > > > > > > >> detail
> > > > > > > >> > > > on
> > > > > > > >> > > > > > FLIP.
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > Thanks for that. I think having the JobManager
> > tell
> > > > the
> > > > > > > >> > > TaskManagers
> > > > > > > >> > > > > the
> > > > > > > >> > > > > > > applicable rules would indeed end up being the
> > best
> > > > > > design.
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > -- about the concerns around consistency raised
> by
> > > > > > Martijn:
> > > > > > > I
> > > > > > > >> > > think a
> > > > > > > >> > > > > lot
> > > > > > > >> > > > > > > of those can be mitigated by using an event time
> > > > > timestamp
> > > > > > > >> from
> > > > > > > >> > > which
> > > > > > > >> > > > > the
> > > > > > > >> > > > > > > rules take effect. The reprocessing scenario,
> for
> > > > > example,
> > > > > > > is
> > > > > > > >> > > covered
> > > > > > > >> > > > > by
> > > > > > > >> > > > > > > this. If a pattern processor should become
> active
> > as
> > > > > soon
> > > > > > as
> > > > > > > >> > > > possible,
> > > > > > > >> > > > > > > there will still be inconsistencies between
> > > > > Taskmanagers,
> > > > > > > but
> > > > > > > >> "as
> > > > > > > >> > > > soon
> > > > > > > >> > > > > as
> > > > > > > >> > > > > > > possible" is vague anyway, which is why I think
> > > that's
> > > > > ok.
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > I think an event timestamp is indeed a really
> > > > important
> > > > > > one.
> > > > > > > >> We
> > > > > > > >> > > also
> > > > > > > >> > > > > used
> > > > > > > >> > > > > > > that in my previous role, with the
> > > > > ruleActivationTimestamp
> > > > > > > >> compared
> > > > > > > >> > > > to
> > > > > > > >> > > > > > > eventtime (well, actually we used Kafka
> logAppend
> > > time
> > > > > > > because
> > > > > > > >> > > > > > > eventtime wasn't always properly set so we used
> > that
> > > > > time
> > > > > > to
> > > > > > > >> > > > overwrite
> > > > > > > >> > > > > > the
> > > > > > > >> > > > > > > eventtime from the event itself).
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > Best regards,
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > Martijn
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> > > > > > > >> knaufk@apache.org>
> > > > > > > >> > > > > > wrote:
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > about the concerns around consistency raised
> by
> > > > > > Martijn: I
> > > > > > > >> think
> > > > > > > >> > > a
> > > > > > > >> > > > > lot
> > > > > > > >> > > > > > of
> > > > > > > >> > > > > > > > those can be mitigated by using an event time
> > > > > timestamp
> > > > > > > from
> > > > > > > >> > > which
> > > > > > > >> > > > > the
> > > > > > > >> > > > > > > > rules take effect. The reprocessing scenario,
> > for
> > > > > > example,
> > > > > > > >> is
> > > > > > > >> > > > covered
> > > > > > > >> > > > > > by
> > > > > > > >> > > > > > > > this. If a pattern processor should become
> > active
> > > as
> > > > > > soon
> > > > > > > as
> > > > > > > >> > > > > possible,
> > > > > > > >> > > > > > > > there will still be inconsistencies between
> > > > > > Taskmanagers,
> > > > > > > >> but "as
> > > > > > > >> > > > > soon
> > > > > > > >> > > > > > as
> > > > > > > >> > > > > > > > possible" is vague anyway, which is why I
> think
> > > > that's
> > > > > > ok.
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > about naming: The naming with
> "PatternProcessor"
> > > > > sounds
> > > > > > > >> good to
> > > > > > > >> > > me.
> > > > > > > >> > > > > > Final
> > > > > > > >> > > > > > > > nit: I would go for CEP#patternProccessors,
> > which
> > > > > would
> > > > > > be
> > > > > > > >> > > > consistent
> > > > > > > >> > > > > > with
> > > > > > > >> > > > > > > > CEP#pattern.
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > I am not sure about one of the rejected
> > > > alternatives:
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > > Have each subtask of an operator make the
> > update
> > > > on
> > > > > > > their
> > > > > > > >> own
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > -
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > It is hard to achieve consistency.
> > > > > > > >> > > > > > > > -
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > Though the time interval that each
> subtask
> > > > makes
> > > > > > the
> > > > > > > >> update
> > > > > > > >> > > > can
> > > > > > > >> > > > > > be
> > > > > > > >> > > > > > > > the same, the absolute time they make
> the
> > > > update
> > > > > > > >> might be
> > > > > > > >> > > > > > different.
> > > > > > > >> > > > > > > > For
> > > > > > > >> > > > > > > > example, one makes updates at 10:00,
> > 10:05,
> > > > etc,
> > > > > > > while
> > > > > > > >> > > > another
> > > > > > > >> > > > > > does
> > > > > > > >> > > > > > > > it at
> > > > > > > >> > > > > > > > 10:01, 10:06. In this case the subtasks
> > > might
> > > > > > never
> > > > > > > >> > > > processing
> > > > > > > >> > > > > > data
> > > > > > > >> > > > > > > > with
> > > > > > > >> > > > > > > > the same set of pattern processors.
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > I would have thought that it is quite easy to
> > poll
> > > > for
> > > > > > the
> > > > > > > >> rules
> > > > > > > >> > > > from
> > > > > > > >> > > > > > each
> > > > > > > >> > > > > > > > Subtask at *about *the same time. So, this
> alone
> > > > does
> > > > > > not
> > > > > > > >> seem to
> > > > > > > >> > > > be
> > > > > > > >> > > > > > > > enough to rule out this option. I've looped in
> > > David
> > > > > > > >> Moravek to
> > > > > > > >> > > get
> > > > > > > >> > > > > his
> > > > > > > >> > > > > > > > opinion of the additional load imposed on the
> > JM.
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > Thanks,
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > Konstantin
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas
> Jiang <
> > > > > > > >> > > > > > nicholasjiang@apache.org>
> > > > > > > >> > > > > > > > wrote:
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > > Hi Yue,
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > Thanks for your feedback of the FLIP. I have
> > > > > addressed
> > > > > > > >> your
> > > > > > > >> > > > > > questions and
> > > > > > > >> > > > > > > > > made a corresponding explanation as follows:
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > > >> > > > to
> > > > > > > >> > > > > > > > update
> > > > > > > >> > > > > > > > > the rules, will it increase the load of JM?
> > For
> > > > > > example,
> > > > > > > >> if the
> > > > > > > >> > > > > user
> > > > > > > >> > > > > > > > wants
> > > > > > > >> > > > > > > > > the updated rule to take effect
> immediately,,
> > > > which
> > > > > > > means
> > > > > > > >> that
> > > > > > > >> > > we
> > > > > > > >> > > > > > need to
> > > > > > > >> > > > > > > > > set a shorter check interval or there is
> > another
> > > > > > > scenario
> > > > > > > >> when
> > > > > > > >> > > > > users
> > > > > > > >> > > > > > > > rarely
> > > > > > > >> > > > > > > > > update the pattern, will the
> > > > > > PatternProcessoerDiscoverer
> > > > > > > >> be in
> > > > > > > >> > > > most
> > > > > > > >> > > > > > of
> > > > > > > >> > > > > > > > the
> > > > > > > >> > > > > > > > > time Do useless checks ? Will a lazy update
> > mode
> > > > > could
> > > > > > > be
> > > > > > > >> used,
> > > > > > > >> > > > > > which the
> > > > > > > >> > > > > > > > > pattern only be updated when triggered by
> the
> > > > user,
> > > > > > and
> > > > > > > do
> > > > > > > >> > > > nothing
> > > > > > > >> > > > > at
> > > > > > > >> > > > > > > > other
> > > > > > > >> > > > > > > > > times?
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > PatternProcessoerDiscoverer is a
> user-defined
> > > > > > interface
> > > > > > > to
> > > > > > > >> > > > discover
> > > > > > > >> > > > > > the
> > > > > > > >> > > > > > > > > PatternProcessor updates. Periodically
> > checking
> > > > the
> > > > > > > >> > > > > PatternProcessor
> > > > > > > >> > > > > > in
> > > > > > > >> > > > > > > > the
> > > > > > > >> > > > > > > > > database is a implementation of the
> > > > > > > >> PatternProcessoerDiscoverer
> > > > > > > >> > > > > > > > interface,
> > > > > > > >> > > > > > > > > which is that periodically querys all the
> > > > > > > PatternProcessor
> > > > > > > >> > > table
> > > > > > > >> > > > in
> > > > > > > >> > > > > > > > certain
> > > > > > > >> > > > > > > > > interval. This implementation indeeds has
> the
> > > > > useless
> > > > > > > >> checks,
> > > > > > > >> > > and
> > > > > > > >> > > > > > could
> > > > > > > >> > > > > > > > > directly integrates the changelog of the
> > table.
> > > In
> > > > > > > >> addition, in
> > > > > > > >> > > > > > addition
> > > > > > > >> > > > > > > > to
> > > > > > > >> > > > > > > > > the implementation of periodically checking
> > the
> > > > > > > database,
> > > > > > > >> there
> > > > > > > >> > > > are
> > > > > > > >> > > > > > other
> > > > > > > >> > > > > > > > > implementations such as the PatternProcessor
> > > that
> > > > > > > provides
> > > > > > > >> > > > Restful
> > > > > > > >> > > > > > > > services
> > > > > > > >> > > > > > > > > to receive updates.
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > -- I still have some confusion about how
> Key
> > > > > > Generating
> > > > > > > >> > > > Opertator
> > > > > > > >> > > > > > and
> > > > > > > >> > > > > > > > > CepOperator (Pattern Matching & Processing
> > > > Operator)
> > > > > > > work
> > > > > > > >> > > > together.
> > > > > > > >> > > > > > If
> > > > > > > >> > > > > > > > > there are N PatternProcessors, will the Key
> > > > > Generating
> > > > > > > >> > > Opertator
> > > > > > > >> > > > > > > > generate N
> > > > > > > >> > > > > > > > > keyedStreams, and then N CepOperator would
> > > process
> > > > > > each
> > > > > > > >> Key
> > > > > > > >> > > > > > separately ?
> > > > > > > >> > > > > > > > Or
> > > > > > > >> > > > > > > > > every CepOperator Task would process all
> > > patterns,
> > > > > if
> > > > > > > so,
> > > > > > > >> does
> > > > > > > >> > > > the
> > > > > > > >> > > > > > key
> > > > > > > >> > > > > > > > type
> > > > > > > >> > > > > > > > > in each PatternProcessor need to be the
> same?
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > Firstly the Pattern Matching & Processing
> > > Operator
> > > > > is
> > > > > > > not
> > > > > > > >> the
> > > > > > > >> > > > > > CepOperator
> > > > > > > >> > > > > > > > > at present, because CepOperator mechanism is
> > > based
> > > > > on
> > > > > > > the
> > > > > > > >> > > > NFAState.
> > > > > > > >> > > > > > > > > Secondly if there are N PatternProcessors,
> the
> > > Key
> > > > > > > >> Generating
> > > > > > > >> > > > > > Opertator
> > > > > > > >> > > > > > > > > combines all the keyedStreams with keyBy()
> > > > > operation,
> > > > > > > >> thus the
> > > > > > > >> > > > > > Pattern
> > > > > > > >> > > > > > > > > Matching & Processing Operator would process
> > all
> > > > the
> > > > > > > >> patterns.
> > > > > > > >> > > In
> > > > > > > >> > > > > > other
> > > > > > > >> > > > > > > > > words, the KeySelector of the
> PatternProcessor
> > > is
> > > > > used
> > > > > > > >> for the
> > > > > > > >> > > > Key
> > > > > > > >> > > > > > > > > Generating Opertator, and the Pattern and
> > > > > > > >> > > PatternProceessFunction
> > > > > > > >> > > > > of
> > > > > > > >> > > > > > the
> > > > > > > >> > > > > > > > > PatternProcessor are used for the Pattern
> > > > Matching &
> > > > > > > >> Processing
> > > > > > > >> > > > > > Operator.
> > > > > > > >> > > > > > > > > Lastly the key type in each PatternProcessor
> > is
> > > > the
> > > > > > > same,
> > > > > > > >> > > > regarded
> > > > > > > >> > > > > as
> > > > > > > >> > > > > > > > > Object type.
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > -- Maybe need to pay attention to it when
> > > > > implementing
> > > > > > > it
> > > > > > > >> .If
> > > > > > > >> > > > some
> > > > > > > >> > > > > > > > Pattern
> > > > > > > >> > > > > > > > > has been removed or updated, will the
> > partially
> > > > > > matched
> > > > > > > >> results
> > > > > > > >> > > > in
> > > > > > > >> > > > > > > > > StateBackend would be clean up or We rely on
> > > state
> > > > > ttl
> > > > > > > to
> > > > > > > >> clean
> > > > > > > >> > > > up
> > > > > > > >> > > > > > these
> > > > > > > >> > > > > > > > > expired states.
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > If certain Pattern has been removed or
> > updated,
> > > > the
> > > > > > > >> partially
> > > > > > > >> > > > > matched
> > > > > > > >> > > > > > > > > results in StateBackend would be clean up
> > until
> > > > the
> > > > > > next
> > > > > > > >> > > > > checkpoint.
> > > > > > > >> > > > > > The
> > > > > > > >> > > > > > > > > partially matched result doesn't depend on
> the
> > > > state
> > > > > > ttl
> > > > > > > >> of the
> > > > > > > >> > > > > > > > > StateBackend.
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > 4. Will the PatternProcessorManager keep all
> > the
> > > > > > active
> > > > > > > >> > > > > > PatternProcessor
> > > > > > > >> > > > > > > > > in memory? We have also Support Multiple
> Rule
> > > and
> > > > > > > Dynamic
> > > > > > > >> Rule
> > > > > > > >> > > > > > Changing.
> > > > > > > >> > > > > > > > > But we are facing such a problem, some
> users’
> > > > usage
> > > > > > > >> scenarios
> > > > > > > >> > > are
> > > > > > > >> > > > > > that
> > > > > > > >> > > > > > > > they
> > > > > > > >> > > > > > > > > want to have their own pattern for each
> > user_id,
> > > > > which
> > > > > > > >> means
> > > > > > > >> > > that
> > > > > > > >> > > > > > there
> > > > > > > >> > > > > > > > > could be thousands of patterns, which would
> > make
> > > > the
> > > > > > > >> > > performance
> > > > > > > >> > > > of
> > > > > > > >> > > > > > > > Pattern
> > > > > > > >> > > > > > > > > Matching very poor. We are also trying to
> > solve
> > > > this
> > > > > > > >> problem.
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > The PatternProcessorManager keeps all the
> > active
> > > > > > > >> > > PatternProcessor
> > > > > > > >> > > > > in
> > > > > > > >> > > > > > > > > memory. For scenarios that they want to have
> > > their
> > > > > own
> > > > > > > >> pattern
> > > > > > > >> > > > for
> > > > > > > >> > > > > > each
> > > > > > > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> > > > > > fine-grained
> > > > > > > >> pattern
> > > > > > > >> > > > of
> > > > > > > >> > > > > > > > > PatternProcessor to solve the performance
> > > problem
> > > > of
> > > > > > the
> > > > > > > >> > > Pattern
> > > > > > > >> > > > > > > > Matching,
> > > > > > > >> > > > > > > > > for example, a pattern corresponds to a
> group
> > of
> > > > > > users?
> > > > > > > >> The
> > > > > > > >> > > > > scenarios
> > > > > > > >> > > > > > > > > mentioned above need to be solved by case by
> > > case.
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > Best,
> > > > > > > >> > > > > > > > > Nicholas Jiang
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > > > > > >> > > > > > > > > > Glad to see the Community's progress in
> > Flink
> > > > CEP.
> > > > > > > After
> > > > > > > >> > > > reading
> > > > > > > >> > > > > > this
> > > > > > > >> > > > > > > > > Flip,
> > > > > > > >> > > > > > > > > > I have few questions, would you please
> take
> > a
> > > > look
> > > > > > ?
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > > > > > >> > > > PatternProcessoerDiscoverer
> > > > > > > >> > > > > to
> > > > > > > >> > > > > > > > > update
> > > > > > > >> > > > > > > > > > the rules, will it increase the load of
> JM?
> > > For
> > > > > > > >> example, if
> > > > > > > >> > > the
> > > > > > > >> > > > > > user
> > > > > > > >> > > > > > > > > wants
> > > > > > > >> > > > > > > > > > the updated rule to take effect
> > immediately,,
> > > > > which
> > > > > > > >> means
> > > > > > > >> > > that
> > > > > > > >> > > > we
> > > > > > > >> > > > > > need
> > > > > > > >> > > > > > > > to
> > > > > > > >> > > > > > > > > > set a shorter check interval or there is
> > > > another
> > > > > > > >> scenario
> > > > > > > >> > > when
> > > > > > > >> > > > > > users
> > > > > > > >> > > > > > > > > > rarely update the pattern, will the
> > > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > > >> > > > > be
> > > > > > > >> > > > > > in
> > > > > > > >> > > > > > > > > most
> > > > > > > >> > > > > > > > > > of the time Do useless checks ? Will a
> lazy
> > > > update
> > > > > > > mode
> > > > > > > >> could
> > > > > > > >> > > > be
> > > > > > > >> > > > > > used,
> > > > > > > >> > > > > > > > > > which the pattern only be updated when
> > > triggered
> > > > > by
> > > > > > > the
> > > > > > > >> user,
> > > > > > > >> > > > and
> > > > > > > >> > > > > > do
> > > > > > > >> > > > > > > > > > nothing at other times ?
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > > > 2. I still have some confusion about how
> > Key
> > > > > > > >> Generating
> > > > > > > >> > > > > > Opertator and
> > > > > > > >> > > > > > > > > > CepOperator (Pattern Matching & Processing
> > > > > Operator)
> > > > > > > >> work
> > > > > > > >> > > > > > together. If
> > > > > > > >> > > > > > > > > > there are N PatternProcessors, will the
> Key
> > > > > > Generating
> > > > > > > >> > > > Opertator
> > > > > > > >> > > > > > > > > generate N
> > > > > > > >> > > > > > > > > > keyedStreams, and then N CepOperator would
> > > > process
> > > > > > > each
> > > > > > > >> Key
> > > > > > > >> > > > > > separately
> > > > > > > >> > > > > > > > ?
> > > > > > > >> > > > > > > > > Or
> > > > > > > >> > > > > > > > > > every CepOperator Task would process all
> > > > patterns,
> > > > > > if
> > > > > > > >> so,
> > > > > > > >> > > does
> > > > > > > >> > > > > the
> > > > > > > >> > > > > > key
> > > > > > > >> > > > > > > > > type
> > > > > > > >> > > > > > > > > > in each PatternProcessor need to be the
> > same ?
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > > > 3. Maybe need to pay attention to it when
> > > > > > implementing
> > > > > > > >> it .If
> > > > > > > >> > > > > some
> > > > > > > >> > > > > > > > > Pattern
> > > > > > > >> > > > > > > > > > has been removed or updateed ,will the
> > > > partially
> > > > > > > >> matched
> > > > > > > >> > > > results
> > > > > > > >> > > > > > in
> > > > > > > >> > > > > > > > > > StateBackend would be clean up or We rely
> on
> > > > state
> > > > > > ttl
> > > > > > > >> to
> > > > > > > >> > > clean
> > > > > > > >> > > > > up
> > > > > > > >> > > > > > > > these
> > > > > > > >> > > > > > > > > > expired states.
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > > > 4. Will the PatternProcessorManager keep
> all
> > > the
> > > > > > > active
> > > > > > > >> > > > > > > > PatternProcessor
> > > > > > > >> > > > > > > > > in
> > > > > > > >> > > > > > > > > > memory ? We have also Support Multiple
> Rule
> > > and
> > > > > > > Dynamic
> > > > > > > >> Rule
> > > > > > > >> > > > > > Changing .
> > > > > > > >> > > > > > > > > > But we are facing such a problem, some
> > users’
> > > > > usage
> > > > > > > >> scenarios
> > > > > > > >> > > > are
> > > > > > > >> > > > > > that
> > > > > > > >> > > > > > > > > they
> > > > > > > >> > > > > > > > > > want to have their own pattern for each
> > > user_id,
> > > > > > which
> > > > > > > >> means
> > > > > > > >> > > > that
> > > > > > > >> > > > > > there
> > > > > > > >> > > > > > > > > > could be thousands of patterns, which
> would
> > > make
> > > > > the
> > > > > > > >> > > > performance
> > > > > > > >> > > > > of
> > > > > > > >> > > > > > > > > Pattern
> > > > > > > >> > > > > > > > > > Matching very poor. We are also trying to
> > > solve
> > > > > this
> > > > > > > >> problem.
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > > > Yunfeng Zhou <flink.zhouyunfeng@gmail.com
> >
> > > > > > > >> 于2021年12月10日周五
> > > > > > > >> > > > > 19:16写道：
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > > > > Hi all，
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > > > I'm opening this thread to propose the
> > > design
> > > > to
> > > > > > > >> support
> > > > > > > >> > > > > multiple
> > > > > > > >> > > > > > > > rule
> > > > > > > >> > > > > > > > > &
> > > > > > > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP
> > > > project,
> > > > > as
> > > > > > > >> > > described
> > > > > > > >> > > > in
> > > > > > > >> > > > > > > > > FLIP-200
> > > > > > > >> > > > > > > > > > > [1]
> > > > > > > >> > > > > > > > > > > .
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > > > Currently Flink CEP only supports
> having a
> > > > > single
> > > > > > > >> pattern
> > > > > > > >> > > > > inside
> > > > > > > >> > > > > > a
> > > > > > > >> > > > > > > > > > > CepOperator and does not support
> changing
> > > the
> > > > > > > pattern
> > > > > > > >> > > > > > dynamically. In
> > > > > > > >> > > > > > > > > order
> > > > > > > >> > > > > > > > > > > to reduce resource consumption and to
> > > > experience
> > > > > > > >> shorter
> > > > > > > >> > > > > downtime
> > > > > > > >> > > > > > > > > during
> > > > > > > >> > > > > > > > > > > pattern updates, there is a growing need
> > in
> > > > the
> > > > > > > >> production
> > > > > > > >> > > > > > > > environment
> > > > > > > >> > > > > > > > > that
> > > > > > > >> > > > > > > > > > > expects CEP to support having multiple
> > > > patterns
> > > > > in
> > > > > > > one
> > > > > > > >> > > > operator
> > > > > > > >> > > > > > and
> > > > > > > >> > > > > > > > to
> > > > > > > >> > > > > > > > > > > support dynamically changing them.
> > > Therefore I
> > > > > > > >> propose to
> > > > > > > >> > > add
> > > > > > > >> > > > > > certain
> > > > > > > >> > > > > > > > > > > infrastructure as described in FLIP-200
> to
> > > > > support
> > > > > > > >> these
> > > > > > > >> > > > > > > > > functionalities.
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > > > Please feel free to reply to this email
> > > > thread.
> > > > > > > >> Looking
> > > > > > > >> > > > forward
> > > > > > > >> > > > > > to
> > > > > > > >> > > > > > > > your
> > > > > > > >> > > > > > > > > > > feedback!
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > > > [1]
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > >
> > > > > > > >> > > > >
> > > > > > > >> > > >
> > > > > > > >> > >
> > > > > > > >>
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > > > Best regards,
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > > > Yunfeng
> > > > > > > >> > > > > > > > > > >
> > > > > > > >> > > > > > > > > >
> > > > > > > >> > > > > > > > >
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > --
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > Konstantin Knauf
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > https://twitter.com/snntrable
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > > > https://github.com/knaufk
> > > > > > > >> > > > > > > >
> > > > > > > >> > > > > > >
> > > > > > > >> > > > > >
> > > > > > > >> > > > >
> > > > > > > >> > > >
> > > > > > > >> > >
> > > > > > > >> > >
> > > > > > > >> > > --
> > > > > > > >> > >
> > > > > > > >> > > Konstantin Knauf
> > > > > > > >> > >
> > > > > > > >> > > https://twitter.com/snntrable
> > > > > > > >> > >
> > > > > > > >> > > https://github.com/knaufk
> > > > > > > >> > >
> > > > > > > >> >
> > > > > > > >>
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Till Rohrmann <tr...@apache.org>.
I think I would scope the effort slightly differently. Note that I might be
missing some requirements or overlook something.
1. Enable Flink to support CEP dynamic patterns
Here I would define the commands and formats for a new CEP pattern. Then I
would extend the CEP operator to understand these commands so that we can
change the CEP patterns dynamically. This should give the building blocks
to set up a job where you can change the CEP patterns by reading from an
arbitrary side input the CEP pattern commands. Note that it will be the
responsibility of the user to ingest the data somehow. This is nothing
Flink is concerned with at this time.
2. Think about how to make the CEP dynamic pattern feature more ergonomic
Here we can pick up the discussion about OC and having a REST ingestion
endpoint in Flink vs. offering tools that live outside of Flink itself. I
could imagine that this could become a separate small project that builds
upon Flink, for example.
Cheers,
Till
On Wed, Jan 5, 2022 at 2:19 PM Becket Qin <be...@gmail.com> wrote:
> Hi Till,
>
> Thanks for the prompt reply. Like you said, we are indeed using the dynamic
> CEP pattern use case to test the existing primitives in Flink to see if
> they can meet the requirements. I fully understand the concern of
> exposing OC as a user interface. Meanwhile I see CEP dynamic patterns as a
> good opportunity to battle test and enhance the OC as a user facing control
> plane which is currently missing. After all, there is no better person than
> ourselves to try it out first.
>
> It is not clear to me whether it is worth continuing the effort of
> supporting dynamic CEP pattern without concluding the control plane
> discussion. Let's say we have a CEP job reading from Kafka. To make this
> work with side-input, a few things need to be done.
>
> 1. In order to support dynamic patterns, users would create another
> Kafka topic as side-input to receive dynamic patterns.
> 2. In order to insert dynamic patterns, users would use a separate web
> server that is provided by us as a separate tool. The web server takes
> http
> requests and sends dynamic pattern records to Kafka via a Kafka sink
> (using
> a KafkaProducer is likely simpler here, though).
> 3. Regarding querying the running dynamic patterns, given Kafka is not
> queryable, users would probably introduce a database and insert the
> patterns there so they can query the running patterns. Maybe this could
> be
> done by the CEP operator side-output, so there is less chance of
> inconsistency between Kafka and the database.
> 4. If the Flink job is to be stopped, the dynamic pattern Kafka topic
> needs to be deleted, the companion web server also needs to be stopped
> (assuming it is not shared with other CEP jobs), and the database table
> storing the dynamic pattern needs to be dropped.
>
> Please correct me if I misunderstood something, but this seems quite
> involved. Moreover, all the work here is going to be thrown away after we
> have OC as a decent user facing control plane in place. And we will likely
> have a backwards incompatible API change here. Given that, I am wondering
> if we should wait until the OC discussion concludes before moving on with
> the dynamic patterns?
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
>
>
> On Wed, Jan 5, 2022 at 5:53 PM Till Rohrmann <tr...@apache.org> wrote:
>
> > Thanks for the detailed explanation Becket.
> >
> > Do you think that an additional dependency is a deal breaker for people
> to
> > use dynamic CEP patterns? At the very least people have to operate some
> > kind of storage/queue system from which the CEP job can read anyway.
> Maybe
> > it could be good enough to provide a REST endpoint (as a separate tool)
> > that can be instantiated with a Flink sink to ingest REST requests
> > into some queue. A general concern I have is that by making the JM a REST
> > ingestion point for data will push another responsibility to Flink and
> > increase the surface area further.
> >
> > For how to handle data that cannot be processed by patterns, I think
> there
> > also exist other solutions. I could imagine that users could define
> > different failover strategies. E.g. one could simply ignore the record,
> the
> > pattern could get deactivated on the affected TM or the processing fails.
> >
> > Maybe we are coupling the dynamic CEP pattern effort too much on where
> the
> > new patterns come from. Maybe we can split these efforts into supporting
> > dynamic CEP patterns on the TM reading from some source and then fork off
> > the discussion about introducing a user controlled control plane to
> Flink.
> > That way we wouldn't block this effort and could discuss more about the
> > exact properties such a user control plane would need to have. What do
> you
> > think?
> >
> > Cheers,
> > Till
> >
> > On Wed, Jan 5, 2022 at 7:18 AM Becket Qin <be...@gmail.com> wrote:
> >
> > > Hi Till,
> > >
> > > Thanks for the comments and questions. To be clear, I am not saying
> that
> > > the side-input stream does not work for the dynamic pattern update use
> > > case. But I think OC is a better solution. The design goal for CEP
> > dynamic
> > > pattern is not only make it work, but also make it user friendly and
> > > extensible. So as a user, I expect the following:
> > >
> > > - Use CEP with dynamic pattern update without depending on external
> > > systems. e.g. updating the pattern by directly talking to the Flink job
> > > itself.
> > > - Some sort of isolation between patterns. e.g. a pattern update
> failure
> > > won't cause other running patterns to fail.
> > > - Easy to query the currently running patterns in the Flink job.
> > > - Extensible to add new features. e.g. apply some pattern to a subset
> of
> > > subtasks. Disable dynamic pattern update during a service window, etc.
> > >
> > > It looks to me that OC is a more promising way to to achieve the above.
> > >
> > > Please also see the reply to your questions inline below.
> > >
> > > > You mentioned that a TM might find out that a pattern is invalid and
> > then
> > > > it could use the 2-way communication with the JM to tell the other
> TMs
> > > that
> > > > the pattern is invalid. How exactly would a TM detect that a pattern
> is
> > > > invalid at data processing time? And assuming that this is possible
> > for a
> > > > single TM, why can't the other TMs not detect this problem? Is it
> > because
> > > > the validity of patterns might depend on data that is different
> between
> > > > TMs?
> > >
> > >
> > > Yes, the TMs are processing different records, so some may encounter
> > issue
> > > while others are running fine, for example, a field may be missing
> from a
> > > record while the pattern requires it. Even if all the TMs have detected
> > the
> > > problem, without a channel to report back the issue, the only thing TMs
> > can
> > > do is either to throw exception and stop processing.
> > >
> > > You also mentioned that deep-learning-on-flink could benefit from an OC
> > > > control plane but I couldn't find the referenced link. Would
> > > > deep-learning-on-flink like to use OCs as a kind of parameter server?
> > > Could
> > > > you elaborate on deep-learning-on-flink's usage of such a feature?
> > >
> > >
> > > deep-learning-on-flink[1] has a general ML cluster abstraction that can
> > run
> > > TF / PyTorch etc. This cluster has a ML master role to manage the
> > > liveliness of all the ML workers which are python processes running
> > > side-by-side with TMs. The ML workers can be PS or Worker of
> TensorFlow.
> > > For example, if 10 TF worker and 5 TF PS nodes are needed, a Flink UDF
> > > operator of parallelism 10 and a Flink Source operator with parallelism
> > = 5
> > > will be created to run the TF worker and TF PS respectively. All the 15
> > > nodes running either PS or Worker are managed by the ML master. Prior
> to
> > > OC, the implementation was having a Source operator with parallelism =
> 1
> > to
> > > run the master; let the ML workers register themselves to the an
> external
> > > ZK so the master can discover them. So basically users have to build
> > their
> > > own control plane. With OC, at very least, we no longer need ZK
> anymore.
> > >
> > > Concerning reprocessing command history and repeatable processing
> > results I
> > > > think there is actually quite a big difference between using a Flink
> > > source
> > > > vs. offering a REST server that can receive command that are
> > distributed
> > > > via the OCs. In the former case we can rely on the external system to
> > > > persist commands whereas in the latter approach we/users have to
> > > implement
> > > > a storage solution on their own (in the simplest case users will
> > probably
> > > > store everything in state which might grow indefinitely if stored as
> a
> > > > changelog).
> > >
> > >
> > > It is true that a Flink Source is easier to provide a change log of
> > > patterns. But there are also downsides. The most prominent one is that
> in
> > > order to update the dynamic pattern, users have to run an external
> system
> > > for the source to read. Or users have to implement a REST Source taking
> > > command directly like a web server. In that case, the service discovery
> > is
> > > again a problem and needs external dependency.
> > > On the other hand, it is not so difficult for OC to store a change log
> > > history. Assuming there are 100 pattern updates / day for a CEP job and
> > one
> > > year of history should be stored. Let's say each pattern change log
> entry
> > > is 1K bytes. The pattern update change log for the entire year is just
> 34
> > > MB, which seems quite small. And users can also query the patterns in
> > > effect via the same endpoint. I think this would provide a good
> > out-of-box
> > > experience in the vast majority of cases. No external dependencies and
> a
> > > single REST endpoint. In rare cases where there is a large amount of
> > > pattern update log. External systems can still be leveraged. One
> > potential
> > > issue might be that a command that has been received but not
> checkpointed
> > > yet may got lost if the job fails over. This can be mitigated by
> allowing
> > > OC to ask JM to trigger a checkpoint (not there yet but may worth
> > > thinking), or simply introduce a *PendingCommit* state for a pattern
> > > indicating it's not committed yet. In the worst case, we can always
> > > fallback to store patterns in external systems such as a database.
> > >
> > > Thanks,
> > >
> > > Jiangjie (Becket) Qin
> > >
> > > [1]
> > >
> > >
> >
> https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
> > >
> > >
> > > On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <tr...@apache.org>
> > wrote:
> > >
> > > > Hi Becket,
> > > >
> > > > Thanks for the explanation. While I do agree that a general 2-way
> > > > communication pattern would be nice to have, I also believe that this
> > > > approach is probably at least one magnitude more complex to realize
> > than
> > > > the side-input approach. Therefore, I really would like to understand
> > why
> > > > such a mechanism is required for the CEP use case.
> > > >
> > > > You mentioned that a TM might find out that a pattern is invalid and
> > then
> > > > it could use the 2-way communication with the JM to tell the other
> TMs
> > > that
> > > > the pattern is invalid. How exactly would a TM detect that a pattern
> is
> > > > invalid at data processing time? And assuming that this is possible
> > for a
> > > > single TM, why can't the other TMs not detect this problem? Is it
> > because
> > > > the validity of patterns might depend on data that is different
> between
> > > > TMs?
> > > >
> > > > You also mentioned that deep-learning-on-flink could benefit from an
> OC
> > > > control plane but I couldn't find the referenced link. Would
> > > > deep-learning-on-flink like to use OCs as a kind of parameter server?
> > > Could
> > > > you elaborate on deep-learning-on-flink's usage of such a feature?
> > > >
> > > > Concerning reprocessing command history and repeatable processing
> > > results I
> > > > think there is actually quite a big difference between using a Flink
> > > source
> > > > vs. offering a REST server that can receive command that are
> > distributed
> > > > via the OCs. In the former case we can rely on the external system to
> > > > persist commands whereas in the latter approach we/users have to
> > > implement
> > > > a storage solution on their own (in the simplest case users will
> > probably
> > > > store everything in state which might grow indefinitely if stored as
> a
> > > > changelog).
> > > >
> > > > Cheers,
> > > > Till
> > > >
> > > > On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com>
> > wrote:
> > > >
> > > > > Hi David,
> > > > >
> > > > > Thanks for sharing your thoughts. Some quick reply to your
> comments:
> > > > >
> > > > > We're still talking about the "web server based"
> > > > > > pattern_processor_discoverer, but what about other use cases? One
> > of
> > > my
> > > > > big
> > > > > > concerns is that user's can not really reuse any part of the
> Flink
> > > > > > ecosystem to implement the discovery logic. For example if they
> > want
> > > to
> > > > > > read patterns from Kafka topic, they need to roll their own
> > > discoverer
> > > > > > based on the vanilla Kafka client. If we're talking about
> > > > extensibility,
> > > > > > should we also make sure that the existing primitives can be
> > reused?
> > > > >
> > > > >
> > > > > KafkaSource is actually more complicated than vanilla KafkaConsumer
> > > from
> > > > > the perspective of consuming Kafka messages. The KafkaSource just
> > helps
> > > > > make it easier for Flink jobs to process these messages. In fact,
> > > > > KafkaConsumer is more powerful than KafkaSource in terms of talking
> > to
> > > > > Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator]
> and
> > > > > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> > > > >
> > > > > This can be done for the side-input as well by filtering invalid
> > > patterns
> > > > > > before the broadcast. You can also send the invalid patterns to
> any
> > > > side
> > > > > > output you want. I have a feeling that we're way too attached to
> > the
> > > > REST
> > > > > > server use case in this discussion. I agree that for that case,
> > this
> > > > > > solution is the most straightforward one.
> > > > >
> > > > >
> > > > > Depending on whether the invalidity is discovered in pattern
> > definition
> > > > > time or data processing time. e.g. A valid pattern with invalid
> data
> > > > which
> > > > > fails to process can only be detected in data processing time. So
> the
> > > > > pattern won't be filtered out before the broadcast.
> > > > >
> > > > > I agree that 2-way communication in the "data-flow like" API is
> > tricky,
> > > > > > because it requires cycles / iterations, which are still not
> really
> > > > > solved
> > > > > > (for a good reason, it's really tough nut to crack). This makes
> me
> > > > think
> > > > > > that the OC may be bit of a "incomplete" workaround for not
> having
> > > > fully
> > > > > > working support for iterations.
> > > > >
> > > > >
> > > > > For example I'm not really confident that the checkpointing of the
> OC
> > > > works
> > > > > > correctly right now, because it doesn't seem to require
> checkpoint
> > > > > barrier
> > > > > > alignment as the regular stream inputs. We also don't have a
> proper
> > > > > support
> > > > > > for watermarking (this is again tricky, because of the cycle).
> > > > >
> > > > >
> > > > > If we decide to go down this road, should we first address some of
> > > these
> > > > > > limitations?
> > > > >
> > > > > I agree. OC is proven to be useful and we should think about how to
> > > > enhance
> > > > > it instead of not using it.
> > > > >
> > > > > If I understand that correctly, this means only the LATEST state of
> > the
> > > > > > patterns (in other words - patterns that are currently in use).
> Is
> > > this
> > > > > > really sufficient for historical re-processing? Can someone for
> > > example
> > > > > > want re-process the data in more of a "temporal join" fashion?
> Also
> > > > AFAIK
> > > > > > historical processing in combination with "coordinator
> checkpoints"
> > > is
> > > > > not
> > > > > > really something that we currently support of the box, are there
> > any
> > > > > plans
> > > > > > on tackling this (my other concern is that this should not go
> > against
> > > > the
> > > > > > "unified batch & stream processing" efforts)?
> > > > >
> > > > > I think in this case, the state would contain the entire pattern
> > update
> > > > > history. Not the final state, but the change log. In fact, it is
> not
> > > > > possible to guarantee the correct result unless you have the entire
> > > > change
> > > > > log. Even with side-input, there still could be late arrivals in
> the
> > > > > pattern update stream, and the only way to correct it is to either
> > have
> > > > all
> > > > > the data reprocessed (with all the pattern change log loaded
> upfront)
> > > or
> > > > > having retraction support.
> > > > >
> > > > > I can imagine that if this should be a concern, we could move the
> > > > execution
> > > > > > of the OC to the task managers. This also makes me thing, that we
> > > > > shouldn't
> > > > > > make any strong assumptions that the OC will always run in the
> > > > JobManager
> > > > > > (this is especially relevant for the embedded web-server use
> case).
> > > > >
> > > > > This is a very good point. I think we should do this. The reason OC
> > is
> > > in
> > > > > JM is based on the assumption that control plane usually have
> little
> > > > > traffic. But if that is not the case, we should move the OC out of
> > JM,
> > > > > maybe to TM.
> > > > >
> > > > >
> > > > >
> > > > > I think the key topic we are discussing is what the Flink control
> > plane
> > > > > should look like, and CEP is just an example use case. There are
> > > > basically
> > > > > two options:
> > > > >
> > > > > 1. Using the side-input / broadcast stream
> > > > > 2. Using the OperatorCoordinator.
> > > > >
> > > > > Although we are having this discussion under the context of
> > supporting
> > > > CEP
> > > > > dynamic pattern update, it would be really helpful to reach
> agreement
> > > on
> > > > > the design principle in general of how Flink should handle similar
> > > > external
> > > > > control demands, a.k.a how to provide a decent control plane in
> Flink
> > > to
> > > > > the users.
> > > > >
> > > > > Here is my take on these two options, based on the requirements of
> a
> > > > > control plane.
> > > > >
> > > > > *Communication Requirements*
> > > > > Flink has two kinds of control planes - in-band and out-of-band.
> > > > > In-band control plane is like watermark and checkpoint marker. It
> > > > requires
> > > > > the entire DAG to be in a consistent state, so the control messages
> > > flow
> > > > > with the data in one direction. This is a one-way control flow.
> > > > > Examples of out-of-band control plane is OC and JM/TM
> communication.
> > > They
> > > > > do not require a global consistency or awareness across the entire
> > DAG.
> > > > >
> > > > > Before OC, neither of these two kinds of control plain was exposed
> to
> > > the
> > > > > users. OC allows the users to leverage the out-of-band control
> plane
> > so
> > > > > they can coordinate across subtasks. This is a more widely used
> > control
> > > > > flow from user defined operator perspective which requires 2-way
> > > > > communication.
> > > > >
> > > > > - side-input stream is one-way communication. Moreover, I don't
> > > think
> > > > > iteration is the right way to address this. Unlike the
> abstraction
> > > of
> > > > > data
> > > > > processing which is a DAG, the control plane may require
> > > communication
> > > > > between arbitrary two operators in different orders. Using
> > > iterations
> > > > > may
> > > > > end up with an explosion of feedback edges that are not only
> > > > > complicated to
> > > > > express, but also hard to debug and maintain.
> > > > > - OC provides a decent 2-way communication mechanism.
> > > > >
> > > > >
> > > > > *Cost for low traffic use case*
> > > > > An important difference between data channel and control channel is
> > > > traffic
> > > > > pattern. Unlike data plane, the control plane is usually idle for
> the
> > > > vast
> > > > > majority of the time with occasional control messages.
> > > > >
> > > > > - One argument to use the side-input / broadcast stream was that
> > > users
> > > > > can reuse the existing connectors. However, most Flink sources
> are
> > > > > designed
> > > > > to handle large throughput of traffic that maintains all the
> > > threads,
> > > > > network connections, etc. Not to say the external resources such
> > as
> > > > > Kafka
> > > > > topics to store the commands.
> > > > > - OC can have a much lower constant cost.
> > > > >
> > > > >
> > > > > *Easy to use*
> > > > > Personally speaking, I think the most simple and user-friendly
> > > interface
> > > > is
> > > > > a REST API that accepts control commands.
> > > > >
> > > > > - One proposal at this point is to have a separate web server
> > > > > independent of the Flink job. In that case, should users
> implement
> > > > that
> > > > > web
> > > > > server? In order to pass the command to the Flink job, does that
> > > mean
> > > > > users
> > > > > should implement a Flink source that can read the commands from
> > the
> > > > web
> > > > > server? Or the web server would send the command to something
> like
> > > > Kafka
> > > > > and let the Flink side-input read from there. There seems to be
> a
> > > lot
> > > > > for
> > > > > the users to do. And it seems an unnecessarily complicated
> system
> > to
> > > > > build
> > > > > to send occasional control messages to a Flink job.
> > > > > - OC can simply be reached via the JM REST API.
> > > > > - e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > > > > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx> would
> > > simply
> > > > > send the Content to the OC of OP_NAME.
> > > > >
> > > > > *Work well with checkpoints*
> > > > >
> > > > > - side-input streams works well with checkpoint, thanks to its
> > > > > compatibility to the DAG abstraction.
> > > > > - The OperatorCoordinator requires more careful design to work
> > well
> > > > with
> > > > > checkpoints. The complexity mostly comes from the 2-way
> > > communication.
> > > > > At
> > > > > this point the OperatorCoordinator message delivery semantic may
> > not
> > > > be
> > > > > as
> > > > > robust as side-input streams. However, I think this is mainly
> due
> > to
> > > > > potential bugs in implementation instead of fundamental design
> > > > problems.
> > > > > Basically the checkpoint semantic should be:
> > > > > - The JM will first checkpoint all the OperatorCoordinator,
> > more
> > > > > specifically for each OperatorCoordinator,
> > > > > - 1) JM blocks the input queue to stop receiving new
> events
> > > from
> > > > > the subtasks.
> > > > > - 2) let all the operator coordinator finish processing
> all
> > > the
> > > > > pending events in the OC input queue.
> > > > > - 3) flush the OC output queue until all the events sent
> are
> > > > > acknowledged.
> > > > > - 3) unblock the input queue, but block the output queue
> > until
> > > > all
> > > > > the subtasks of the OC finish checkpoints.
> > > > > - The JM starts a normal checkpoint starting from the Source.
> > > > > - If an operator has a coordinator, and it has sent some
> > > events
> > > > to
> > > > > the OC but has not been acknowledged. These events need to
> > be
> > > > > put into the
> > > > > subtasks' checkpoint.
> > > > > - After all the subtasks of an operator finishes checkpoint,
> > the
> > > > > output queue of the corresponding OC can be unblocked.
> > > > > It looks that the above protocol would let OC have a clear
> > > checkpoint
> > > > > semantic. And this complexity seems must for 2-way
> communication.
> > I
> > > > > think
> > > > > we are able to hide the above protocol from users by having an
> > > > abstract
> > > > > OC
> > > > > implementation.
> > > > >
> > > > >
> > > > > *Reprocess command history and repeatable processing results*
> > > > > This seems not something generally required for a control plane.
> But
> > if
> > > > the
> > > > > control plane changes the data processing behavior, there might be
> > some
> > > > use
> > > > > case. Just like the CEP pattern update. In order to do this, users
> > will
> > > > > need to provide a full command history to the operators. That
> > consists
> > > of
> > > > > two steps:
> > > > >
> > > > > 1. get the full command history. (Flink Source V.S. Custom way
> to
> > > > > retrieve command history.)
> > > > > 2. send them to the operators. (Side-input V.S. OC/Operator
> > > > > communication)l
> > > > >
> > > > > I actually don't feel much difference between these two options. I
> am
> > > not
> > > > > sure if a Flink source is necessarily simpler than the user
> > implemented
> > > > > logic. For example, if all the changes are just written in a
> database
> > > > > table. From the user's perspective, I feel fine with querying the
> DB
> > by
> > > > > myself using something like JDBC (or use KafkaConsumer to read the
> > > > pattern
> > > > > history from a Kafka topic) and send all the pattern change history
> > to
> > > > the
> > > > > operators before they start to process the actual events.
> > > > >
> > > > > *Stability impact to the Flink Job*
> > > > > I agree this is a valid concern. There is only one JM and currently
> > OC
> > > > runs
> > > > > there, which may potentially cause JM crash and result in job
> > failure.
> > > > > Running in TM may have a less impact. So I think it makes sense to
> > run
> > > OC
> > > > > in TM. However, this is more of how we can implement OC to make it
> > more
> > > > > robust. It does not forfeit the other semantic and user experience
> > > > benefits
> > > > > mentioned above.
> > > > >
> > > > >
> > > > > To sum up:
> > > > > 1. Regardless of whether CEP chooses OC or side-input stream, a
> > decent
> > > > > 2-way communication control plane seems really helpful and has been
> > > > proven
> > > > > by quite a few existing use cases. To me the question is how to
> make
> > it
> > > > > more robust, not whether we should use it or not.
> > > > > 2. As for CEP, if we assume OC will be robust enough, personally I
> > feel
> > > > OC
> > > > > is a better fit than side-input mainly because of the simplicity
> and
> > > > > extensibility.
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Jiangjie (Becket) Qin
> > > > >
> > > > >
> > > > > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org>
> > wrote:
> > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > sorry for the late reply, vacation season ;) I'm still not 100%
> > sold
> > > on
> > > > > > choosing the OC for this use-case, but on the other hand I don't
> > have
> > > > > > strong arguments against it. Few more questions / thoughts:
> > > > > >
> > > > > > We're still talking about the "web server based"
> > > > > > pattern_processor_discoverer, but what about other use cases? One
> > of
> > > my
> > > > > big
> > > > > > concerns is that user's can not really reuse any part of the
> Flink
> > > > > > ecosystem to implement the discovery logic. For example if they
> > want
> > > to
> > > > > > read patterns from Kafka topic, they need to roll their own
> > > discoverer
> > > > > > based on the vanilla Kafka client. If we're talking about
> > > > extensibility,
> > > > > > should we also make sure that the existing primitives can be
> > reused?
> > > > > >
> > > > > > For instance, the example I gave in my previous email seems not
> > > easily
> > > > > > > achievable with side-input / broadcast streams: a single
> invalid
> > > > > pattern
> > > > > > > detected on a TM can be disabled elegantly globally without
> > > crashing
> > > > > the
> > > > > > > entire Flink job.
> > > > > >
> > > > > >
> > > > > > This can be done for the side-input as well by filtering invalid
> > > > patterns
> > > > > > before the broadcast. You can also send the invalid patterns to
> any
> > > > side
> > > > > > output you want. I have a feeling that we're way too attached to
> > the
> > > > REST
> > > > > > server use case in this discussion. I agree that for that case,
> > this
> > > > > > solution is the most straightforward one.
> > > > > >
> > > > > > OC is a 2-way communication mechanism, i.e. a subtask can also
> send
> > > > > > > OperatorEvent to the coordinator to report its owns status, so
> > that
> > > > the
> > > > > > > coordinator can act accordingly.
> > > > > > >
> > > > > >
> > > > > > I agree that 2-way communication in the "data-flow like" API is
> > > tricky,
> > > > > > because it requires cycles / iterations, which are still not
> really
> > > > > solved
> > > > > > (for a good reason, it's really tough nut to crack). This makes
> me
> > > > think
> > > > > > that the OC may be bit of a "incomplete" workaround for not
> having
> > > > fully
> > > > > > working support for iterations.
> > > > > >
> > > > > > For example I'm not really confident that the checkpointing of
> the
> > OC
> > > > > works
> > > > > > correctly right now, because it doesn't seem to require
> checkpoint
> > > > > barrier
> > > > > > alignment as the regular stream inputs. We also don't have a
> proper
> > > > > support
> > > > > > for watermarking (this is again tricky, because of the cycle).
> > > > > >
> > > > > > If we decide to go down this road, should we first address some
> of
> > > > these
> > > > > > limitations?
> > > > > >
> > > > > > OperatorCoordinator will checkpoint the full amount of
> > > PatternProcessor
> > > > > > > data. For the reprocessing of historical data, you can read the
> > > > > > > PatternProcessor snapshots saved by this checkpoint from a
> > certain
> > > > > > > historical checkpoint, and then recreate the historical data
> > > through
> > > > > > these
> > > > > > > PatternProcessor snapshots.
> > > > > > >
> > > > > >
> > > > > > If I understand that correctly, this means only the LATEST state
> of
> > > the
> > > > > > patterns (in other words - patterns that are currently in use).
> Is
> > > this
> > > > > > really sufficient for historical re-processing? Can someone for
> > > example
> > > > > > want re-process the data in more of a "temporal join" fashion?
> Also
> > > > AFAIK
> > > > > > historical processing in combination with "coordinator
> checkpoints"
> > > is
> > > > > not
> > > > > > really something that we currently support of the box, are there
> > any
> > > > > plans
> > > > > > on tackling this (my other concern is that this should not go
> > against
> > > > the
> > > > > > "unified batch & stream processing" efforts)?
> > > > > >
> > > > > > I do agree that having the user defined control logic defined in
> > the
> > > JM
> > > > > > > increases the chance of instability.
> > > > > > >
> > > > > >
> > > > > > I can imagine that if this should be a concern, we could move the
> > > > > execution
> > > > > > of the OC to the task managers. This also makes me thing, that we
> > > > > shouldn't
> > > > > > make any strong assumptions that the OC will always run in the
> > > > JobManager
> > > > > > (this is especially relevant for the embedded web-server use
> case).
> > > > > >
> > > > > > If an agreement is reached on OperatorCoodinator, I will start
> the
> > > > voting
> > > > > > > thread.
> > > > > > >
> > > > > >
> > > > > > As for the vote, I'd would be great if we can wait until the next
> > > week
> > > > as
> > > > > > many people took vacation until end of the year.
> > > > > >
> > > > > > Overall, I really like the feature, this will be a great addition
> > to
> > > > > Flink.
> > > > > >
> > > > > > Best,
> > > > > > D.
> > > > > >
> > > > > >
> > > > > >
> > > > > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <
> > > martijn@ververica.com
> > > > >
> > > > > > wrote:
> > > > > >
> > > > > > > Hi all,
> > > > > > >
> > > > > > > I can understand the need for a control plane mechanism. I'm
> not
> > > the
> > > > > > > technical go-to person for questions on the
> OperatorCoordinator,
> > > but
> > > > I
> > > > > > > would expect that we could offer those interfaces from Flink
> but
> > > > > > shouldn't
> > > > > > > recommend running user-code in the JobManager itself. I think
> the
> > > > user
> > > > > > code
> > > > > > > (like a webserver) should run outside of Flink (like via a
> > sidecar)
> > > > and
> > > > > > use
> > > > > > > only the provided interfaces to communicate.
> > > > > > >
> > > > > > > I would like to get @David Morávek <dm...@apache.org> opinion
> on
> > > the
> > > > > > > technical part.
> > > > > > >
> > > > > > > Best regards,
> > > > > > >
> > > > > > > Martijn
> > > > > > >
> > > > > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> > > > nicholasjiang@apache.org
> > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > >> Hi Konstantin, Becket, Martijn,
> > > > > > >>
> > > > > > >> Thanks for sharing your feedback. What other concerns do you
> > have
> > > > > about
> > > > > > >> OperatorCoodinator? If an agreement is reached on
> > > > OperatorCoodinator,
> > > > > I
> > > > > > >> will start the voting thread.
> > > > > > >>
> > > > > > >> Best,
> > > > > > >> Nicholas Jiang
> > > > > > >>
> > > > > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > > > > >> > Hi Konstantin,
> > > > > > >> >
> > > > > > >> > Thanks for sharing your thoughts. Please see the reply
> inline
> > > > below.
> > > > > > >> >
> > > > > > >> > Thanks,
> > > > > > >> >
> > > > > > >> > Jiangjie (Becket) Qin
> > > > > > >> >
> > > > > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> > > > knaufk@apache.org
> > > > > >
> > > > > > >> wrote:
> > > > > > >> >
> > > > > > >> > > Hi Becket, Hi Nicholas,
> > > > > > >> > >
> > > > > > >> > > Thanks for joining the discussion.
> > > > > > >> > >
> > > > > > >> > > 1 ) Personally, I would argue that we should only run user
> > > code
> > > > in
> > > > > > the
> > > > > > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems
> wrong
> > to
> > > > me
> > > > > to
> > > > > > >> > > encourage users to e.g. run a webserver on the Jobmanager,
> > or
> > > > > > >> continuously
> > > > > > >> > > read patterns from a Kafka Topic on the Jobmanager, but
> both
> > > of
> > > > > > these
> > > > > > >> I see
> > > > > > >> > > happening with the current design. We've had lots of
> issues
> > > with
> > > > > > >> > > classloading leaks and other stability issues on the
> > > Jobmanager
> > > > > and
> > > > > > >> making
> > > > > > >> > > this more complicated, if there is another way, seems
> > > > unnecessary.
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > I think the key question here is what primitive does Flink
> > > provide
> > > > > to
> > > > > > >> > facilitate the user implementation of their own control
> logic
> > /
> > > > > > control
> > > > > > >> > plane? It looks that previously, Flink assumes that all the
> > user
> > > > > logic
> > > > > > >> is
> > > > > > >> > just data processing logic without any control /
> coordination
> > > > > > >> requirements.
> > > > > > >> > However, it turns out that a decent control plane
> abstraction
> > is
> > > > > > >> required
> > > > > > >> > in association with the data processing logic in many cases,
> > > > > including
> > > > > > >> > Source / Sink and other user defined operators in general.
> The
> > > > fact
> > > > > > >> that we
> > > > > > >> > ended up with adding the SplitEnumerator and GlobalCommitter
> > are
> > > > > just
> > > > > > >> two
> > > > > > >> > examples of the demand of such coordination among user
> defined
> > > > > logics.
> > > > > > >> > There are other cases that we see in ecosystem projects,
> such
> > as
> > > > > > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > > > > > >> >
> > > > > > >> > Such control plane primitives are critical to the
> > extensibility
> > > > of a
> > > > > > >> > project. If we look at other projects, exposing such control
> > > plane
> > > > > > >> logic is
> > > > > > >> > quite common. For example, Hadoop ended up with exposing
> YARN
> > > as a
> > > > > > >> public
> > > > > > >> > API to the users, which is extremely popular. Kafka
> consumers
> > > > > exposed
> > > > > > >> the
> > > > > > >> > consumer group rebalance logic to the users via
> > > > > > >> ConsumerPartitionAssigner,
> > > > > > >> > which is also a control plane primitive.
> > > > > > >> >
> > > > > > >> > To me it is more important to think about how we can improve
> > the
> > > > > > >> stability
> > > > > > >> > of such a control plane mechanism, instead of simply saying
> no
> > > to
> > > > > the
> > > > > > >> users.
> > > > > > >> >
> > > > > > >> >
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > > 2) In addition, I suspect that, over time we will have to
> > > > > implement
> > > > > > >> all the
> > > > > > >> > > functionality that regular sources already provide around
> > > > > > consistency
> > > > > > >> > > (watermarks, checkpointing) for the
> > > PatternProcessorCoordinator,
> > > > > > too.
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > I think OperatorCoordinator should have a generic
> > communication
> > > > > > >> mechanism
> > > > > > >> > for all the operators, not specific to Source. We should
> > > probably
> > > > > have
> > > > > > >> an
> > > > > > >> > AbstractOperatorCoordinator help dealing with the
> > communication
> > > > > layer,
> > > > > > >> and
> > > > > > >> > leave the state maintenance and event handling logic to the
> > user
> > > > > code.
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > > 3) I understand that running on the Jobmanager is easier
> if
> > > you
> > > > > want
> > > > > > >> to
> > > > > > >> > > launch a REST server directly. Here my question would be:
> > does
> > > > > this
> > > > > > >> really
> > > > > > >> > > need to be solved inside of Flink or couldn't you start a
> > > > > webserver
> > > > > > >> next to
> > > > > > >> > > Flink? If we start using the Jobmanager as a REST server
> > users
> > > > > will
> > > > > > >> expect
> > > > > > >> > > that e.g. it is highly available and can be load balanced
> > and
> > > we
> > > > > > >> quickly
> > > > > > >> > > need to think about aspects that we never wanted to think
> > > about
> > > > in
> > > > > > the
> > > > > > >> > > context of a Flink Jobmanager.
> > > > > > >> > >
> > > > > > >> >
> > > > > > >> > I think the REST API is just for receiving commands
> targeting
> > a
> > > > > > running
> > > > > > >> > Flink job. If the job fails, the REST API would be useless.
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > > So, can you elaborate a bit more, why a
> side-input/broadcast
> > > > > stream
> > > > > > is
> > > > > > >> > >
> > > > > > >> > > a) more difficult
> > > > > > >> > > b) has vague semantics (To me semantics of a stream-stream
> > > seem
> > > > > > >> clearer
> > > > > > >> > > when it comes to out-of-orderness, late data, reprocessing
> > or
> > > > > batch
> > > > > > >> > > execution mode.)
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > I do agree that having the user defined control logic
> defined
> > in
> > > > the
> > > > > > JM
> > > > > > >> > increases the chance of instability. In that case, we may
> > think
> > > of
> > > > > > other
> > > > > > >> > solutions and I am fully open to that. But the side-input /
> > > > > broadcast
> > > > > > >> > stream seems more like a bandaid instead of a carefully
> > designed
> > > > > > control
> > > > > > >> > plane mechanism.
> > > > > > >> >
> > > > > > >> > A decent control plane requires two-way communication, so
> > > > > information
> > > > > > >> can
> > > > > > >> > be reported / collected from the entity being controlled,
> and
> > > the
> > > > > > >> > coordinator / controller can send decisions or commands to
> the
> > > > > > entities
> > > > > > >> > accordingly, just like our TM / JM communication. IIUC, this
> > is
> > > > not
> > > > > > >> > achievable with the existing side-input / broadcast stream
> as
> > > both
> > > > > of
> > > > > > >> them
> > > > > > >> > are one-way communication mechanisms. For instance, the
> > example
> > > I
> > > > > gave
> > > > > > >> in
> > > > > > >> > my previous email seems not easily achievable with
> side-input
> > /
> > > > > > >> broadcast
> > > > > > >> > streams: a single invalid pattern detected on a TM can be
> > > disabled
> > > > > > >> > elegantly globally without crashing the entire Flink job.
> > > > > > >> >
> > > > > > >> >
> > > > > > >> > > Cheers,
> > > > > > >> > >
> > > > > > >> > > Konstantin
> > > > > > >> > >
> > > > > > >> > >
> > > > > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> > > > becket.qin@gmail.com
> > > > > >
> > > > > > >> wrote:
> > > > > > >> > >
> > > > > > >> > > > Hi folks,
> > > > > > >> > > >
> > > > > > >> > > > I just finished reading the previous emails. It was a
> good
> > > > > > >> discussion.
> > > > > > >> > > Here
> > > > > > >> > > > are my two cents:
> > > > > > >> > > >
> > > > > > >> > > > *Is OperatorCoordinator a public API?*
> > > > > > >> > > > Regarding the OperatorCoordinator, although it is marked
> > as
> > > > > > internal
> > > > > > >> > > > interface at this point, I intended to make it a public
> > > > > interface
> > > > > > >> when
> > > > > > >> > > add
> > > > > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> > > > communication
> > > > > > >> mechanism
> > > > > > >> > > > that enables many use cases, Source / Sink / TF on
> Flink /
> > > CEP
> > > > > > here
> > > > > > >> > > again.
> > > > > > >> > > > To my understanding, OC was marked as internal because
> we
> > > > think
> > > > > it
> > > > > > >> is not
> > > > > > >> > > > stable enough yet. We may need to fortify the
> > OperatorEvent
> > > > > > delivery
> > > > > > >> > > > semantic a little bit so it works well with checkpoint
> in
> > > > > general.
> > > > > > >> > > >
> > > > > > >> > > > I think it is a valid concern that user code running in
> JM
> > > may
> > > > > > cause
> > > > > > >> > > > instability. However, not providing this communication
> > > > mechanism
> > > > > > >> only
> > > > > > >> > > makes
> > > > > > >> > > > a lot of use case even harder to implement. So it seems
> > that
> > > > > > having
> > > > > > >> the
> > > > > > >> > > OC
> > > > > > >> > > > exposed to end users brings more benefits than harm to
> > > Flink.
> > > > At
> > > > > > >> the end
> > > > > > >> > > of
> > > > > > >> > > > the day, users have many ways to crash a Flink job if
> they
> > > do
> > > > > not
> > > > > > >> write
> > > > > > >> > > > proper code. So making those who know what they do happy
> > > seems
> > > > > > more
> > > > > > >> > > > important here.
> > > > > > >> > > >
> > > > > > >> > > > *OperatorCoordinator V.S. side-input / broadcast stream*
> > > > > > >> > > > I think both of them can achieve the goal of dynamic
> > > patterns.
> > > > > The
> > > > > > >> main
> > > > > > >> > > > difference is the extensibility.
> > > > > > >> > > >
> > > > > > >> > > > OC is a 2-way communication mechanism, i.e. a subtask
> can
> > > also
> > > > > > send
> > > > > > >> > > > OperatorEvent to the coordinator to report its owns
> > status,
> > > so
> > > > > > that
> > > > > > >> the
> > > > > > >> > > > coordinator can act accordingly. This is sometimes
> useful.
> > > For
> > > > > > >> example, a
> > > > > > >> > > > single invalid pattern can be disabled elegantly without
> > > > > crashing
> > > > > > >> the
> > > > > > >> > > > entire Flink job. In the future, if we allow users to
> send
> > > > > > external
> > > > > > >> > > command
> > > > > > >> > > > to OC via JM, a default self-contained implementation
> can
> > > just
> > > > > > >> update the
> > > > > > >> > > > pattern via the REST API without external dependencies.
> > > > > > >> > > >
> > > > > > >> > > > Another reason I personally prefer OC is because it is
> an
> > > > > explicit
> > > > > > >> > > control
> > > > > > >> > > > plain mechanism, where as the side-input / broadcast
> > stream
> > > > has
> > > > > > are
> > > > > > >> more
> > > > > > >> > > > vague semantic.
> > > > > > >> > > >
> > > > > > >> > > > Thanks,
> > > > > > >> > > >
> > > > > > >> > > > Jiangjie (Becket) Qin
> > > > > > >> > > >
> > > > > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> > > > dmvk@apache.org>
> > > > > > >> wrote:
> > > > > > >> > > >
> > > > > > >> > > > > Hi Yunfeng,
> > > > > > >> > > > >
> > > > > > >> > > > > thanks for drafting this FLIP, this will be a great
> > > addition
> > > > > > into
> > > > > > >> the
> > > > > > >> > > CEP
> > > > > > >> > > > > toolbox!
> > > > > > >> > > > >
> > > > > > >> > > > > Apart from running user code in JM, which want to
> avoid
> > in
> > > > > > >> general, I'd
> > > > > > >> > > > > have one more another concern about using the
> > > > > > OperatorCoordinator
> > > > > > >> and
> > > > > > >> > > > that
> > > > > > >> > > > > is re-processing of the historical data. Any thoughts
> > > about
> > > > > how
> > > > > > >> this
> > > > > > >> > > will
> > > > > > >> > > > > work with the OC?
> > > > > > >> > > > >
> > > > > > >> > > > > I have a slight feeling that a side-input (custom
> > source /
> > > > > > >> operator +
> > > > > > >> > > > > broadcast) would a better fit for this case. This
> would
> > > > > simplify
> > > > > > >> the
> > > > > > >> > > > > consistency concerns (watermarks + pushback) and the
> > > > > > >> re-processing of
> > > > > > >> > > > > historical data.
> > > > > > >> > > > >
> > > > > > >> > > > > Best,
> > > > > > >> > > > > D.
> > > > > > >> > > > >
> > > > > > >> > > > >
> > > > > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > > > > >> > > nicholasjiang@apache.org
> > > > > > >> > > > >
> > > > > > >> > > > > wrote:
> > > > > > >> > > > >
> > > > > > >> > > > > > Hi Konstantin, Martijn
> > > > > > >> > > > > >
> > > > > > >> > > > > > Thanks for the detailed feedback in the discussion.
> > > What I
> > > > > > >> still have
> > > > > > >> > > > > left
> > > > > > >> > > > > > to answer/reply to:
> > > > > > >> > > > > >
> > > > > > >> > > > > > -- Martijn: Just to be sure, this indeed would mean
> > that
> > > > if
> > > > > > for
> > > > > > >> > > > whatever
> > > > > > >> > > > > > reason the heartbeat timeout, it would crash the
> job,
> > > > right?
> > > > > > >> > > > > >
> > > > > > >> > > > > > IMO, if for whatever reason the heartbeat timeout,
> it
> > > > > couldn't
> > > > > > >> check
> > > > > > >> > > > the
> > > > > > >> > > > > > PatternProcessor consistency between the
> > > > OperatorCoordinator
> > > > > > >> and the
> > > > > > >> > > > > > subtasks so that the job would be crashed.
> > > > > > >> > > > > >
> > > > > > >> > > > > > -- Konstantin: What I was concerned about is that we
> > > > > basically
> > > > > > >> let
> > > > > > >> > > > users
> > > > > > >> > > > > > run a UserFunction in the OperatorCoordinator, which
> > it
> > > > does
> > > > > > >> not seem
> > > > > > >> > > > to
> > > > > > >> > > > > > have been designed for.
> > > > > > >> > > > > >
> > > > > > >> > > > > > In general, we have reached an agreement on the
> design
> > > of
> > > > > this
> > > > > > >> FLIP,
> > > > > > >> > > > but
> > > > > > >> > > > > > there are some concerns on the OperatorCoordinator,
> > > about
> > > > > > >> whether
> > > > > > >> > > > > basically
> > > > > > >> > > > > > let users run a UserFunction in the
> > OperatorCoordinator
> > > is
> > > > > > >> designed
> > > > > > >> > > for
> > > > > > >> > > > > > OperatorCoordinator. We would like to invite Becket
> > Qin
> > > > who
> > > > > is
> > > > > > >> the
> > > > > > >> > > > author
> > > > > > >> > > > > > of OperatorCoordinator to help us to answer this
> > > concern.
> > > > > > >> > > > > >
> > > > > > >> > > > > > Best,
> > > > > > >> > > > > > Nicholas Jiang
> > > > > > >> > > > > >
> > > > > > >> > > > > >
> > > > > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > > > > >> > > > > > > Hi all,
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > Really like the discussion on this topic moving
> > > > forward. I
> > > > > > >> really
> > > > > > >> > > > think
> > > > > > >> > > > > > > this feature will be much appreciated by the Flink
> > > > users.
> > > > > > >> What I
> > > > > > >> > > > still
> > > > > > >> > > > > > have
> > > > > > >> > > > > > > left to answer/reply to:
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > -- Good point. If for whatever reason the
> different
> > > > > > >> taskmanagers
> > > > > > >> > > > can't
> > > > > > >> > > > > > get
> > > > > > >> > > > > > > the latest rule, the Operator Coordinator could
> > send a
> > > > > > >> heartbeat to
> > > > > > >> > > > all
> > > > > > >> > > > > > > taskmanagers with the latest rules and check the
> > > > heartbeat
> > > > > > >> response
> > > > > > >> > > > > from
> > > > > > >> > > > > > > all the taskmanagers whether the latest rules of
> the
> > > > > > >> taskmanager is
> > > > > > >> > > > > equal
> > > > > > >> > > > > > > to these of the Operator Coordinator.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > Just to be sure, this indeed would mean that if
> for
> > > > > whatever
> > > > > > >> reason
> > > > > > >> > > > the
> > > > > > >> > > > > > > heartbeat timeout, it would crash the job, right?
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > -- We have consided about the solution mentioned
> > > above.
> > > > In
> > > > > > >> this
> > > > > > >> > > > > > solution, I
> > > > > > >> > > > > > > have some questions about how to guarantee the
> > > > consistency
> > > > > > of
> > > > > > >> the
> > > > > > >> > > > rule
> > > > > > >> > > > > > > between each TaskManager. By having a coodinator
> in
> > > the
> > > > > > >> JobManager
> > > > > > >> > > to
> > > > > > >> > > > > > > centrally manage the latest rules, the latest
> rules
> > of
> > > > all
> > > > > > >> > > > TaskManagers
> > > > > > >> > > > > > are
> > > > > > >> > > > > > > consistent with those of the JobManager, so as to
> > > avoid
> > > > > the
> > > > > > >> > > > > > inconsistencies
> > > > > > >> > > > > > > that may be encountered in the above solution. Can
> > you
> > > > > > >> introduce
> > > > > > >> > > how
> > > > > > >> > > > > this
> > > > > > >> > > > > > > solution guarantees the consistency of the rules?
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > The consistency that we could guarantee was based
> on
> > > how
> > > > > > >> often each
> > > > > > >> > > > > > > TaskManager would do a refresh and how often we
> > would
> > > > > > accept a
> > > > > > >> > > > refresh
> > > > > > >> > > > > to
> > > > > > >> > > > > > > fail. We set the refresh time to a relatively
> short
> > > one
> > > > > (30
> > > > > > >> > > seconds)
> > > > > > >> > > > > and
> > > > > > >> > > > > > > maximum failures to 3. That meant that we could
> > > > guarantee
> > > > > > that
> > > > > > >> > > rules
> > > > > > >> > > > > > would
> > > > > > >> > > > > > > be updated in < 2 minutes or else the job would
> > crash.
> > > > > That
> > > > > > >> was
> > > > > > >> > > > > > sufficient
> > > > > > >> > > > > > > for our use cases. This also really depends on how
> > big
> > > > > your
> > > > > > >> cluster
> > > > > > >> > > > > is. I
> > > > > > >> > > > > > > can imagine that if you have a large scale cluster
> > > that
> > > > > you
> > > > > > >> want to
> > > > > > >> > > > > run,
> > > > > > >> > > > > > > you don't want to DDOS the backend system where
> you
> > > have
> > > > > > your
> > > > > > >> rules
> > > > > > >> > > > > > stored.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > -- In summary, the current design is that
> JobManager
> > > > tells
> > > > > > all
> > > > > > >> > > > > > TaskManagers
> > > > > > >> > > > > > > the latest rules through OperatorCoodinator, and
> > will
> > > > > > >> initiate a
> > > > > > >> > > > > > heartbeat
> > > > > > >> > > > > > > to check whether the latest rules on each
> > TaskManager
> > > > are
> > > > > > >> > > consistent.
> > > > > > >> > > > > We
> > > > > > >> > > > > > > will describe how to deal with the Failover
> scenario
> > > in
> > > > > more
> > > > > > >> detail
> > > > > > >> > > > on
> > > > > > >> > > > > > FLIP.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > Thanks for that. I think having the JobManager
> tell
> > > the
> > > > > > >> > > TaskManagers
> > > > > > >> > > > > the
> > > > > > >> > > > > > > applicable rules would indeed end up being the
> best
> > > > > design.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > -- about the concerns around consistency raised by
> > > > > Martijn:
> > > > > > I
> > > > > > >> > > think a
> > > > > > >> > > > > lot
> > > > > > >> > > > > > > of those can be mitigated by using an event time
> > > > timestamp
> > > > > > >> from
> > > > > > >> > > which
> > > > > > >> > > > > the
> > > > > > >> > > > > > > rules take effect. The reprocessing scenario, for
> > > > example,
> > > > > > is
> > > > > > >> > > covered
> > > > > > >> > > > > by
> > > > > > >> > > > > > > this. If a pattern processor should become active
> as
> > > > soon
> > > > > as
> > > > > > >> > > > possible,
> > > > > > >> > > > > > > there will still be inconsistencies between
> > > > Taskmanagers,
> > > > > > but
> > > > > > >> "as
> > > > > > >> > > > soon
> > > > > > >> > > > > as
> > > > > > >> > > > > > > possible" is vague anyway, which is why I think
> > that's
> > > > ok.
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > I think an event timestamp is indeed a really
> > > important
> > > > > one.
> > > > > > >> We
> > > > > > >> > > also
> > > > > > >> > > > > used
> > > > > > >> > > > > > > that in my previous role, with the
> > > > ruleActivationTimestamp
> > > > > > >> compared
> > > > > > >> > > > to
> > > > > > >> > > > > > > eventtime (well, actually we used Kafka logAppend
> > time
> > > > > > because
> > > > > > >> > > > > > > eventtime wasn't always properly set so we used
> that
> > > > time
> > > > > to
> > > > > > >> > > > overwrite
> > > > > > >> > > > > > the
> > > > > > >> > > > > > > eventtime from the event itself).
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > Best regards,
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > Martijn
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> > > > > > >> knaufk@apache.org>
> > > > > > >> > > > > > wrote:
> > > > > > >> > > > > > >
> > > > > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > about the concerns around consistency raised by
> > > > > Martijn: I
> > > > > > >> think
> > > > > > >> > > a
> > > > > > >> > > > > lot
> > > > > > >> > > > > > of
> > > > > > >> > > > > > > > those can be mitigated by using an event time
> > > > timestamp
> > > > > > from
> > > > > > >> > > which
> > > > > > >> > > > > the
> > > > > > >> > > > > > > > rules take effect. The reprocessing scenario,
> for
> > > > > example,
> > > > > > >> is
> > > > > > >> > > > covered
> > > > > > >> > > > > > by
> > > > > > >> > > > > > > > this. If a pattern processor should become
> active
> > as
> > > > > soon
> > > > > > as
> > > > > > >> > > > > possible,
> > > > > > >> > > > > > > > there will still be inconsistencies between
> > > > > Taskmanagers,
> > > > > > >> but "as
> > > > > > >> > > > > soon
> > > > > > >> > > > > > as
> > > > > > >> > > > > > > > possible" is vague anyway, which is why I think
> > > that's
> > > > > ok.
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > about naming: The naming with "PatternProcessor"
> > > > sounds
> > > > > > >> good to
> > > > > > >> > > me.
> > > > > > >> > > > > > Final
> > > > > > >> > > > > > > > nit: I would go for CEP#patternProccessors,
> which
> > > > would
> > > > > be
> > > > > > >> > > > consistent
> > > > > > >> > > > > > with
> > > > > > >> > > > > > > > CEP#pattern.
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > I am not sure about one of the rejected
> > > alternatives:
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > > Have each subtask of an operator make the
> update
> > > on
> > > > > > their
> > > > > > >> own
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > -
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > It is hard to achieve consistency.
> > > > > > >> > > > > > > > -
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > Though the time interval that each subtask
> > > makes
> > > > > the
> > > > > > >> update
> > > > > > >> > > > can
> > > > > > >> > > > > > be
> > > > > > >> > > > > > > > the same, the absolute time they make the
> > > update
> > > > > > >> might be
> > > > > > >> > > > > > different.
> > > > > > >> > > > > > > > For
> > > > > > >> > > > > > > > example, one makes updates at 10:00,
> 10:05,
> > > etc,
> > > > > > while
> > > > > > >> > > > another
> > > > > > >> > > > > > does
> > > > > > >> > > > > > > > it at
> > > > > > >> > > > > > > > 10:01, 10:06. In this case the subtasks
> > might
> > > > > never
> > > > > > >> > > > processing
> > > > > > >> > > > > > data
> > > > > > >> > > > > > > > with
> > > > > > >> > > > > > > > the same set of pattern processors.
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > I would have thought that it is quite easy to
> poll
> > > for
> > > > > the
> > > > > > >> rules
> > > > > > >> > > > from
> > > > > > >> > > > > > each
> > > > > > >> > > > > > > > Subtask at *about *the same time. So, this alone
> > > does
> > > > > not
> > > > > > >> seem to
> > > > > > >> > > > be
> > > > > > >> > > > > > > > enough to rule out this option. I've looped in
> > David
> > > > > > >> Moravek to
> > > > > > >> > > get
> > > > > > >> > > > > his
> > > > > > >> > > > > > > > opinion of the additional load imposed on the
> JM.
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > Thanks,
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > Konstantin
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas Jiang <
> > > > > > >> > > > > > nicholasjiang@apache.org>
> > > > > > >> > > > > > > > wrote:
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > > Hi Yue,
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > Thanks for your feedback of the FLIP. I have
> > > > addressed
> > > > > > >> your
> > > > > > >> > > > > > questions and
> > > > > > >> > > > > > > > > made a corresponding explanation as follows:
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > >> > > > to
> > > > > > >> > > > > > > > update
> > > > > > >> > > > > > > > > the rules, will it increase the load of JM?
> For
> > > > > example,
> > > > > > >> if the
> > > > > > >> > > > > user
> > > > > > >> > > > > > > > wants
> > > > > > >> > > > > > > > > the updated rule to take effect immediately,,
> > > which
> > > > > > means
> > > > > > >> that
> > > > > > >> > > we
> > > > > > >> > > > > > need to
> > > > > > >> > > > > > > > > set a shorter check interval or there is
> another
> > > > > > scenario
> > > > > > >> when
> > > > > > >> > > > > users
> > > > > > >> > > > > > > > rarely
> > > > > > >> > > > > > > > > update the pattern, will the
> > > > > PatternProcessoerDiscoverer
> > > > > > >> be in
> > > > > > >> > > > most
> > > > > > >> > > > > > of
> > > > > > >> > > > > > > > the
> > > > > > >> > > > > > > > > time Do useless checks ? Will a lazy update
> mode
> > > > could
> > > > > > be
> > > > > > >> used,
> > > > > > >> > > > > > which the
> > > > > > >> > > > > > > > > pattern only be updated when triggered by the
> > > user,
> > > > > and
> > > > > > do
> > > > > > >> > > > nothing
> > > > > > >> > > > > at
> > > > > > >> > > > > > > > other
> > > > > > >> > > > > > > > > times?
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > PatternProcessoerDiscoverer is a user-defined
> > > > > interface
> > > > > > to
> > > > > > >> > > > discover
> > > > > > >> > > > > > the
> > > > > > >> > > > > > > > > PatternProcessor updates. Periodically
> checking
> > > the
> > > > > > >> > > > > PatternProcessor
> > > > > > >> > > > > > in
> > > > > > >> > > > > > > > the
> > > > > > >> > > > > > > > > database is a implementation of the
> > > > > > >> PatternProcessoerDiscoverer
> > > > > > >> > > > > > > > interface,
> > > > > > >> > > > > > > > > which is that periodically querys all the
> > > > > > PatternProcessor
> > > > > > >> > > table
> > > > > > >> > > > in
> > > > > > >> > > > > > > > certain
> > > > > > >> > > > > > > > > interval. This implementation indeeds has the
> > > > useless
> > > > > > >> checks,
> > > > > > >> > > and
> > > > > > >> > > > > > could
> > > > > > >> > > > > > > > > directly integrates the changelog of the
> table.
> > In
> > > > > > >> addition, in
> > > > > > >> > > > > > addition
> > > > > > >> > > > > > > > to
> > > > > > >> > > > > > > > > the implementation of periodically checking
> the
> > > > > > database,
> > > > > > >> there
> > > > > > >> > > > are
> > > > > > >> > > > > > other
> > > > > > >> > > > > > > > > implementations such as the PatternProcessor
> > that
> > > > > > provides
> > > > > > >> > > > Restful
> > > > > > >> > > > > > > > services
> > > > > > >> > > > > > > > > to receive updates.
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > -- I still have some confusion about how Key
> > > > > Generating
> > > > > > >> > > > Opertator
> > > > > > >> > > > > > and
> > > > > > >> > > > > > > > > CepOperator (Pattern Matching & Processing
> > > Operator)
> > > > > > work
> > > > > > >> > > > together.
> > > > > > >> > > > > > If
> > > > > > >> > > > > > > > > there are N PatternProcessors, will the Key
> > > > Generating
> > > > > > >> > > Opertator
> > > > > > >> > > > > > > > generate N
> > > > > > >> > > > > > > > > keyedStreams, and then N CepOperator would
> > process
> > > > > each
> > > > > > >> Key
> > > > > > >> > > > > > separately ?
> > > > > > >> > > > > > > > Or
> > > > > > >> > > > > > > > > every CepOperator Task would process all
> > patterns,
> > > > if
> > > > > > so,
> > > > > > >> does
> > > > > > >> > > > the
> > > > > > >> > > > > > key
> > > > > > >> > > > > > > > type
> > > > > > >> > > > > > > > > in each PatternProcessor need to be the same?
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > Firstly the Pattern Matching & Processing
> > Operator
> > > > is
> > > > > > not
> > > > > > >> the
> > > > > > >> > > > > > CepOperator
> > > > > > >> > > > > > > > > at present, because CepOperator mechanism is
> > based
> > > > on
> > > > > > the
> > > > > > >> > > > NFAState.
> > > > > > >> > > > > > > > > Secondly if there are N PatternProcessors, the
> > Key
> > > > > > >> Generating
> > > > > > >> > > > > > Opertator
> > > > > > >> > > > > > > > > combines all the keyedStreams with keyBy()
> > > > operation,
> > > > > > >> thus the
> > > > > > >> > > > > > Pattern
> > > > > > >> > > > > > > > > Matching & Processing Operator would process
> all
> > > the
> > > > > > >> patterns.
> > > > > > >> > > In
> > > > > > >> > > > > > other
> > > > > > >> > > > > > > > > words, the KeySelector of the PatternProcessor
> > is
> > > > used
> > > > > > >> for the
> > > > > > >> > > > Key
> > > > > > >> > > > > > > > > Generating Opertator, and the Pattern and
> > > > > > >> > > PatternProceessFunction
> > > > > > >> > > > > of
> > > > > > >> > > > > > the
> > > > > > >> > > > > > > > > PatternProcessor are used for the Pattern
> > > Matching &
> > > > > > >> Processing
> > > > > > >> > > > > > Operator.
> > > > > > >> > > > > > > > > Lastly the key type in each PatternProcessor
> is
> > > the
> > > > > > same,
> > > > > > >> > > > regarded
> > > > > > >> > > > > as
> > > > > > >> > > > > > > > > Object type.
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > -- Maybe need to pay attention to it when
> > > > implementing
> > > > > > it
> > > > > > >> .If
> > > > > > >> > > > some
> > > > > > >> > > > > > > > Pattern
> > > > > > >> > > > > > > > > has been removed or updated, will the
> partially
> > > > > matched
> > > > > > >> results
> > > > > > >> > > > in
> > > > > > >> > > > > > > > > StateBackend would be clean up or We rely on
> > state
> > > > ttl
> > > > > > to
> > > > > > >> clean
> > > > > > >> > > > up
> > > > > > >> > > > > > these
> > > > > > >> > > > > > > > > expired states.
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > If certain Pattern has been removed or
> updated,
> > > the
> > > > > > >> partially
> > > > > > >> > > > > matched
> > > > > > >> > > > > > > > > results in StateBackend would be clean up
> until
> > > the
> > > > > next
> > > > > > >> > > > > checkpoint.
> > > > > > >> > > > > > The
> > > > > > >> > > > > > > > > partially matched result doesn't depend on the
> > > state
> > > > > ttl
> > > > > > >> of the
> > > > > > >> > > > > > > > > StateBackend.
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > 4. Will the PatternProcessorManager keep all
> the
> > > > > active
> > > > > > >> > > > > > PatternProcessor
> > > > > > >> > > > > > > > > in memory? We have also Support Multiple Rule
> > and
> > > > > > Dynamic
> > > > > > >> Rule
> > > > > > >> > > > > > Changing.
> > > > > > >> > > > > > > > > But we are facing such a problem, some users’
> > > usage
> > > > > > >> scenarios
> > > > > > >> > > are
> > > > > > >> > > > > > that
> > > > > > >> > > > > > > > they
> > > > > > >> > > > > > > > > want to have their own pattern for each
> user_id,
> > > > which
> > > > > > >> means
> > > > > > >> > > that
> > > > > > >> > > > > > there
> > > > > > >> > > > > > > > > could be thousands of patterns, which would
> make
> > > the
> > > > > > >> > > performance
> > > > > > >> > > > of
> > > > > > >> > > > > > > > Pattern
> > > > > > >> > > > > > > > > Matching very poor. We are also trying to
> solve
> > > this
> > > > > > >> problem.
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > The PatternProcessorManager keeps all the
> active
> > > > > > >> > > PatternProcessor
> > > > > > >> > > > > in
> > > > > > >> > > > > > > > > memory. For scenarios that they want to have
> > their
> > > > own
> > > > > > >> pattern
> > > > > > >> > > > for
> > > > > > >> > > > > > each
> > > > > > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> > > > > fine-grained
> > > > > > >> pattern
> > > > > > >> > > > of
> > > > > > >> > > > > > > > > PatternProcessor to solve the performance
> > problem
> > > of
> > > > > the
> > > > > > >> > > Pattern
> > > > > > >> > > > > > > > Matching,
> > > > > > >> > > > > > > > > for example, a pattern corresponds to a group
> of
> > > > > users?
> > > > > > >> The
> > > > > > >> > > > > scenarios
> > > > > > >> > > > > > > > > mentioned above need to be solved by case by
> > case.
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > Best,
> > > > > > >> > > > > > > > > Nicholas Jiang
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > > > > >> > > > > > > > > > Glad to see the Community's progress in
> Flink
> > > CEP.
> > > > > > After
> > > > > > >> > > > reading
> > > > > > >> > > > > > this
> > > > > > >> > > > > > > > > Flip,
> > > > > > >> > > > > > > > > > I have few questions, would you please take
> a
> > > look
> > > > > ?
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > > > > >> > > > PatternProcessoerDiscoverer
> > > > > > >> > > > > to
> > > > > > >> > > > > > > > > update
> > > > > > >> > > > > > > > > > the rules, will it increase the load of JM?
> > For
> > > > > > >> example, if
> > > > > > >> > > the
> > > > > > >> > > > > > user
> > > > > > >> > > > > > > > > wants
> > > > > > >> > > > > > > > > > the updated rule to take effect
> immediately,,
> > > > which
> > > > > > >> means
> > > > > > >> > > that
> > > > > > >> > > > we
> > > > > > >> > > > > > need
> > > > > > >> > > > > > > > to
> > > > > > >> > > > > > > > > > set a shorter check interval or there is
> > > another
> > > > > > >> scenario
> > > > > > >> > > when
> > > > > > >> > > > > > users
> > > > > > >> > > > > > > > > > rarely update the pattern, will the
> > > > > > >> > > PatternProcessoerDiscoverer
> > > > > > >> > > > > be
> > > > > > >> > > > > > in
> > > > > > >> > > > > > > > > most
> > > > > > >> > > > > > > > > > of the time Do useless checks ? Will a lazy
> > > update
> > > > > > mode
> > > > > > >> could
> > > > > > >> > > > be
> > > > > > >> > > > > > used,
> > > > > > >> > > > > > > > > > which the pattern only be updated when
> > triggered
> > > > by
> > > > > > the
> > > > > > >> user,
> > > > > > >> > > > and
> > > > > > >> > > > > > do
> > > > > > >> > > > > > > > > > nothing at other times ?
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > > > 2. I still have some confusion about how
> Key
> > > > > > >> Generating
> > > > > > >> > > > > > Opertator and
> > > > > > >> > > > > > > > > > CepOperator (Pattern Matching & Processing
> > > > Operator)
> > > > > > >> work
> > > > > > >> > > > > > together. If
> > > > > > >> > > > > > > > > > there are N PatternProcessors, will the Key
> > > > > Generating
> > > > > > >> > > > Opertator
> > > > > > >> > > > > > > > > generate N
> > > > > > >> > > > > > > > > > keyedStreams, and then N CepOperator would
> > > process
> > > > > > each
> > > > > > >> Key
> > > > > > >> > > > > > separately
> > > > > > >> > > > > > > > ?
> > > > > > >> > > > > > > > > Or
> > > > > > >> > > > > > > > > > every CepOperator Task would process all
> > > patterns,
> > > > > if
> > > > > > >> so,
> > > > > > >> > > does
> > > > > > >> > > > > the
> > > > > > >> > > > > > key
> > > > > > >> > > > > > > > > type
> > > > > > >> > > > > > > > > > in each PatternProcessor need to be the
> same ?
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > > > 3. Maybe need to pay attention to it when
> > > > > implementing
> > > > > > >> it .If
> > > > > > >> > > > > some
> > > > > > >> > > > > > > > > Pattern
> > > > > > >> > > > > > > > > > has been removed or updateed ,will the
> > > partially
> > > > > > >> matched
> > > > > > >> > > > results
> > > > > > >> > > > > > in
> > > > > > >> > > > > > > > > > StateBackend would be clean up or We rely on
> > > state
> > > > > ttl
> > > > > > >> to
> > > > > > >> > > clean
> > > > > > >> > > > > up
> > > > > > >> > > > > > > > these
> > > > > > >> > > > > > > > > > expired states.
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > > > 4. Will the PatternProcessorManager keep all
> > the
> > > > > > active
> > > > > > >> > > > > > > > PatternProcessor
> > > > > > >> > > > > > > > > in
> > > > > > >> > > > > > > > > > memory ? We have also Support Multiple Rule
> > and
> > > > > > Dynamic
> > > > > > >> Rule
> > > > > > >> > > > > > Changing .
> > > > > > >> > > > > > > > > > But we are facing such a problem, some
> users’
> > > > usage
> > > > > > >> scenarios
> > > > > > >> > > > are
> > > > > > >> > > > > > that
> > > > > > >> > > > > > > > > they
> > > > > > >> > > > > > > > > > want to have their own pattern for each
> > user_id,
> > > > > which
> > > > > > >> means
> > > > > > >> > > > that
> > > > > > >> > > > > > there
> > > > > > >> > > > > > > > > > could be thousands of patterns, which would
> > make
> > > > the
> > > > > > >> > > > performance
> > > > > > >> > > > > of
> > > > > > >> > > > > > > > > Pattern
> > > > > > >> > > > > > > > > > Matching very poor. We are also trying to
> > solve
> > > > this
> > > > > > >> problem.
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > > > Yunfeng Zhou <fl...@gmail.com>
> > > > > > >> 于2021年12月10日周五
> > > > > > >> > > > > 19:16写道：
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > > > > Hi all，
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > > > I'm opening this thread to propose the
> > design
> > > to
> > > > > > >> support
> > > > > > >> > > > > multiple
> > > > > > >> > > > > > > > rule
> > > > > > >> > > > > > > > > &
> > > > > > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP
> > > project,
> > > > as
> > > > > > >> > > described
> > > > > > >> > > > in
> > > > > > >> > > > > > > > > FLIP-200
> > > > > > >> > > > > > > > > > > [1]
> > > > > > >> > > > > > > > > > > .
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > > > Currently Flink CEP only supports having a
> > > > single
> > > > > > >> pattern
> > > > > > >> > > > > inside
> > > > > > >> > > > > > a
> > > > > > >> > > > > > > > > > > CepOperator and does not support changing
> > the
> > > > > > pattern
> > > > > > >> > > > > > dynamically. In
> > > > > > >> > > > > > > > > order
> > > > > > >> > > > > > > > > > > to reduce resource consumption and to
> > > experience
> > > > > > >> shorter
> > > > > > >> > > > > downtime
> > > > > > >> > > > > > > > > during
> > > > > > >> > > > > > > > > > > pattern updates, there is a growing need
> in
> > > the
> > > > > > >> production
> > > > > > >> > > > > > > > environment
> > > > > > >> > > > > > > > > that
> > > > > > >> > > > > > > > > > > expects CEP to support having multiple
> > > patterns
> > > > in
> > > > > > one
> > > > > > >> > > > operator
> > > > > > >> > > > > > and
> > > > > > >> > > > > > > > to
> > > > > > >> > > > > > > > > > > support dynamically changing them.
> > Therefore I
> > > > > > >> propose to
> > > > > > >> > > add
> > > > > > >> > > > > > certain
> > > > > > >> > > > > > > > > > > infrastructure as described in FLIP-200 to
> > > > support
> > > > > > >> these
> > > > > > >> > > > > > > > > functionalities.
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > > > Please feel free to reply to this email
> > > thread.
> > > > > > >> Looking
> > > > > > >> > > > forward
> > > > > > >> > > > > > to
> > > > > > >> > > > > > > > your
> > > > > > >> > > > > > > > > > > feedback!
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > > > [1]
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > >
> > > > > > >> > > > >
> > > > > > >> > > >
> > > > > > >> > >
> > > > > > >>
> > > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > > > Best regards,
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > > > Yunfeng
> > > > > > >> > > > > > > > > > >
> > > > > > >> > > > > > > > > >
> > > > > > >> > > > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > --
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > Konstantin Knauf
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > https://twitter.com/snntrable
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > > > https://github.com/knaufk
> > > > > > >> > > > > > > >
> > > > > > >> > > > > > >
> > > > > > >> > > > > >
> > > > > > >> > > > >
> > > > > > >> > > >
> > > > > > >> > >
> > > > > > >> > >
> > > > > > >> > > --
> > > > > > >> > >
> > > > > > >> > > Konstantin Knauf
> > > > > > >> > >
> > > > > > >> > > https://twitter.com/snntrable
> > > > > > >> > >
> > > > > > >> > > https://github.com/knaufk
> > > > > > >> > >
> > > > > > >> >
> > > > > > >>
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Becket Qin <be...@gmail.com>.
Hi Till,
Thanks for the prompt reply. Like you said, we are indeed using the dynamic
CEP pattern use case to test the existing primitives in Flink to see if
they can meet the requirements. I fully understand the concern of
exposing OC as a user interface. Meanwhile I see CEP dynamic patterns as a
good opportunity to battle test and enhance the OC as a user facing control
plane which is currently missing. After all, there is no better person than
ourselves to try it out first.
It is not clear to me whether it is worth continuing the effort of
supporting dynamic CEP pattern without concluding the control plane
discussion. Let's say we have a CEP job reading from Kafka. To make this
work with side-input, a few things need to be done.
1. In order to support dynamic patterns, users would create another
Kafka topic as side-input to receive dynamic patterns.
2. In order to insert dynamic patterns, users would use a separate web
server that is provided by us as a separate tool. The web server takes http
requests and sends dynamic pattern records to Kafka via a Kafka sink (using
a KafkaProducer is likely simpler here, though).
3. Regarding querying the running dynamic patterns, given Kafka is not
queryable, users would probably introduce a database and insert the
patterns there so they can query the running patterns. Maybe this could be
done by the CEP operator side-output, so there is less chance of
inconsistency between Kafka and the database.
4. If the Flink job is to be stopped, the dynamic pattern Kafka topic
needs to be deleted, the companion web server also needs to be stopped
(assuming it is not shared with other CEP jobs), and the database table
storing the dynamic pattern needs to be dropped.
Please correct me if I misunderstood something, but this seems quite
involved. Moreover, all the work here is going to be thrown away after we
have OC as a decent user facing control plane in place. And we will likely
have a backwards incompatible API change here. Given that, I am wondering
if we should wait until the OC discussion concludes before moving on with
the dynamic patterns?
Thanks,
Jiangjie (Becket) Qin
On Wed, Jan 5, 2022 at 5:53 PM Till Rohrmann <tr...@apache.org> wrote:
> Thanks for the detailed explanation Becket.
>
> Do you think that an additional dependency is a deal breaker for people to
> use dynamic CEP patterns? At the very least people have to operate some
> kind of storage/queue system from which the CEP job can read anyway. Maybe
> it could be good enough to provide a REST endpoint (as a separate tool)
> that can be instantiated with a Flink sink to ingest REST requests
> into some queue. A general concern I have is that by making the JM a REST
> ingestion point for data will push another responsibility to Flink and
> increase the surface area further.
>
> For how to handle data that cannot be processed by patterns, I think there
> also exist other solutions. I could imagine that users could define
> different failover strategies. E.g. one could simply ignore the record, the
> pattern could get deactivated on the affected TM or the processing fails.
>
> Maybe we are coupling the dynamic CEP pattern effort too much on where the
> new patterns come from. Maybe we can split these efforts into supporting
> dynamic CEP patterns on the TM reading from some source and then fork off
> the discussion about introducing a user controlled control plane to Flink.
> That way we wouldn't block this effort and could discuss more about the
> exact properties such a user control plane would need to have. What do you
> think?
>
> Cheers,
> Till
>
> On Wed, Jan 5, 2022 at 7:18 AM Becket Qin <be...@gmail.com> wrote:
>
> > Hi Till,
> >
> > Thanks for the comments and questions. To be clear, I am not saying that
> > the side-input stream does not work for the dynamic pattern update use
> > case. But I think OC is a better solution. The design goal for CEP
> dynamic
> > pattern is not only make it work, but also make it user friendly and
> > extensible. So as a user, I expect the following:
> >
> > - Use CEP with dynamic pattern update without depending on external
> > systems. e.g. updating the pattern by directly talking to the Flink job
> > itself.
> > - Some sort of isolation between patterns. e.g. a pattern update failure
> > won't cause other running patterns to fail.
> > - Easy to query the currently running patterns in the Flink job.
> > - Extensible to add new features. e.g. apply some pattern to a subset of
> > subtasks. Disable dynamic pattern update during a service window, etc.
> >
> > It looks to me that OC is a more promising way to to achieve the above.
> >
> > Please also see the reply to your questions inline below.
> >
> > > You mentioned that a TM might find out that a pattern is invalid and
> then
> > > it could use the 2-way communication with the JM to tell the other TMs
> > that
> > > the pattern is invalid. How exactly would a TM detect that a pattern is
> > > invalid at data processing time? And assuming that this is possible
> for a
> > > single TM, why can't the other TMs not detect this problem? Is it
> because
> > > the validity of patterns might depend on data that is different between
> > > TMs?
> >
> >
> > Yes, the TMs are processing different records, so some may encounter
> issue
> > while others are running fine, for example, a field may be missing from a
> > record while the pattern requires it. Even if all the TMs have detected
> the
> > problem, without a channel to report back the issue, the only thing TMs
> can
> > do is either to throw exception and stop processing.
> >
> > You also mentioned that deep-learning-on-flink could benefit from an OC
> > > control plane but I couldn't find the referenced link. Would
> > > deep-learning-on-flink like to use OCs as a kind of parameter server?
> > Could
> > > you elaborate on deep-learning-on-flink's usage of such a feature?
> >
> >
> > deep-learning-on-flink[1] has a general ML cluster abstraction that can
> run
> > TF / PyTorch etc. This cluster has a ML master role to manage the
> > liveliness of all the ML workers which are python processes running
> > side-by-side with TMs. The ML workers can be PS or Worker of TensorFlow.
> > For example, if 10 TF worker and 5 TF PS nodes are needed, a Flink UDF
> > operator of parallelism 10 and a Flink Source operator with parallelism
> = 5
> > will be created to run the TF worker and TF PS respectively. All the 15
> > nodes running either PS or Worker are managed by the ML master. Prior to
> > OC, the implementation was having a Source operator with parallelism = 1
> to
> > run the master; let the ML workers register themselves to the an external
> > ZK so the master can discover them. So basically users have to build
> their
> > own control plane. With OC, at very least, we no longer need ZK anymore.
> >
> > Concerning reprocessing command history and repeatable processing
> results I
> > > think there is actually quite a big difference between using a Flink
> > source
> > > vs. offering a REST server that can receive command that are
> distributed
> > > via the OCs. In the former case we can rely on the external system to
> > > persist commands whereas in the latter approach we/users have to
> > implement
> > > a storage solution on their own (in the simplest case users will
> probably
> > > store everything in state which might grow indefinitely if stored as a
> > > changelog).
> >
> >
> > It is true that a Flink Source is easier to provide a change log of
> > patterns. But there are also downsides. The most prominent one is that in
> > order to update the dynamic pattern, users have to run an external system
> > for the source to read. Or users have to implement a REST Source taking
> > command directly like a web server. In that case, the service discovery
> is
> > again a problem and needs external dependency.
> > On the other hand, it is not so difficult for OC to store a change log
> > history. Assuming there are 100 pattern updates / day for a CEP job and
> one
> > year of history should be stored. Let's say each pattern change log entry
> > is 1K bytes. The pattern update change log for the entire year is just 34
> > MB, which seems quite small. And users can also query the patterns in
> > effect via the same endpoint. I think this would provide a good
> out-of-box
> > experience in the vast majority of cases. No external dependencies and a
> > single REST endpoint. In rare cases where there is a large amount of
> > pattern update log. External systems can still be leveraged. One
> potential
> > issue might be that a command that has been received but not checkpointed
> > yet may got lost if the job fails over. This can be mitigated by allowing
> > OC to ask JM to trigger a checkpoint (not there yet but may worth
> > thinking), or simply introduce a *PendingCommit* state for a pattern
> > indicating it's not committed yet. In the worst case, we can always
> > fallback to store patterns in external systems such as a database.
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> > [1]
> >
> >
> https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
> >
> >
> > On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <tr...@apache.org>
> wrote:
> >
> > > Hi Becket,
> > >
> > > Thanks for the explanation. While I do agree that a general 2-way
> > > communication pattern would be nice to have, I also believe that this
> > > approach is probably at least one magnitude more complex to realize
> than
> > > the side-input approach. Therefore, I really would like to understand
> why
> > > such a mechanism is required for the CEP use case.
> > >
> > > You mentioned that a TM might find out that a pattern is invalid and
> then
> > > it could use the 2-way communication with the JM to tell the other TMs
> > that
> > > the pattern is invalid. How exactly would a TM detect that a pattern is
> > > invalid at data processing time? And assuming that this is possible
> for a
> > > single TM, why can't the other TMs not detect this problem? Is it
> because
> > > the validity of patterns might depend on data that is different between
> > > TMs?
> > >
> > > You also mentioned that deep-learning-on-flink could benefit from an OC
> > > control plane but I couldn't find the referenced link. Would
> > > deep-learning-on-flink like to use OCs as a kind of parameter server?
> > Could
> > > you elaborate on deep-learning-on-flink's usage of such a feature?
> > >
> > > Concerning reprocessing command history and repeatable processing
> > results I
> > > think there is actually quite a big difference between using a Flink
> > source
> > > vs. offering a REST server that can receive command that are
> distributed
> > > via the OCs. In the former case we can rely on the external system to
> > > persist commands whereas in the latter approach we/users have to
> > implement
> > > a storage solution on their own (in the simplest case users will
> probably
> > > store everything in state which might grow indefinitely if stored as a
> > > changelog).
> > >
> > > Cheers,
> > > Till
> > >
> > > On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com>
> wrote:
> > >
> > > > Hi David,
> > > >
> > > > Thanks for sharing your thoughts. Some quick reply to your comments:
> > > >
> > > > We're still talking about the "web server based"
> > > > > pattern_processor_discoverer, but what about other use cases? One
> of
> > my
> > > > big
> > > > > concerns is that user's can not really reuse any part of the Flink
> > > > > ecosystem to implement the discovery logic. For example if they
> want
> > to
> > > > > read patterns from Kafka topic, they need to roll their own
> > discoverer
> > > > > based on the vanilla Kafka client. If we're talking about
> > > extensibility,
> > > > > should we also make sure that the existing primitives can be
> reused?
> > > >
> > > >
> > > > KafkaSource is actually more complicated than vanilla KafkaConsumer
> > from
> > > > the perspective of consuming Kafka messages. The KafkaSource just
> helps
> > > > make it easier for Flink jobs to process these messages. In fact,
> > > > KafkaConsumer is more powerful than KafkaSource in terms of talking
> to
> > > > Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator] and
> > > > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> > > >
> > > > This can be done for the side-input as well by filtering invalid
> > patterns
> > > > > before the broadcast. You can also send the invalid patterns to any
> > > side
> > > > > output you want. I have a feeling that we're way too attached to
> the
> > > REST
> > > > > server use case in this discussion. I agree that for that case,
> this
> > > > > solution is the most straightforward one.
> > > >
> > > >
> > > > Depending on whether the invalidity is discovered in pattern
> definition
> > > > time or data processing time. e.g. A valid pattern with invalid data
> > > which
> > > > fails to process can only be detected in data processing time. So the
> > > > pattern won't be filtered out before the broadcast.
> > > >
> > > > I agree that 2-way communication in the "data-flow like" API is
> tricky,
> > > > > because it requires cycles / iterations, which are still not really
> > > > solved
> > > > > (for a good reason, it's really tough nut to crack). This makes me
> > > think
> > > > > that the OC may be bit of a "incomplete" workaround for not having
> > > fully
> > > > > working support for iterations.
> > > >
> > > >
> > > > For example I'm not really confident that the checkpointing of the OC
> > > works
> > > > > correctly right now, because it doesn't seem to require checkpoint
> > > > barrier
> > > > > alignment as the regular stream inputs. We also don't have a proper
> > > > support
> > > > > for watermarking (this is again tricky, because of the cycle).
> > > >
> > > >
> > > > If we decide to go down this road, should we first address some of
> > these
> > > > > limitations?
> > > >
> > > > I agree. OC is proven to be useful and we should think about how to
> > > enhance
> > > > it instead of not using it.
> > > >
> > > > If I understand that correctly, this means only the LATEST state of
> the
> > > > > patterns (in other words - patterns that are currently in use). Is
> > this
> > > > > really sufficient for historical re-processing? Can someone for
> > example
> > > > > want re-process the data in more of a "temporal join" fashion? Also
> > > AFAIK
> > > > > historical processing in combination with "coordinator checkpoints"
> > is
> > > > not
> > > > > really something that we currently support of the box, are there
> any
> > > > plans
> > > > > on tackling this (my other concern is that this should not go
> against
> > > the
> > > > > "unified batch & stream processing" efforts)?
> > > >
> > > > I think in this case, the state would contain the entire pattern
> update
> > > > history. Not the final state, but the change log. In fact, it is not
> > > > possible to guarantee the correct result unless you have the entire
> > > change
> > > > log. Even with side-input, there still could be late arrivals in the
> > > > pattern update stream, and the only way to correct it is to either
> have
> > > all
> > > > the data reprocessed (with all the pattern change log loaded upfront)
> > or
> > > > having retraction support.
> > > >
> > > > I can imagine that if this should be a concern, we could move the
> > > execution
> > > > > of the OC to the task managers. This also makes me thing, that we
> > > > shouldn't
> > > > > make any strong assumptions that the OC will always run in the
> > > JobManager
> > > > > (this is especially relevant for the embedded web-server use case).
> > > >
> > > > This is a very good point. I think we should do this. The reason OC
> is
> > in
> > > > JM is based on the assumption that control plane usually have little
> > > > traffic. But if that is not the case, we should move the OC out of
> JM,
> > > > maybe to TM.
> > > >
> > > >
> > > >
> > > > I think the key topic we are discussing is what the Flink control
> plane
> > > > should look like, and CEP is just an example use case. There are
> > > basically
> > > > two options:
> > > >
> > > > 1. Using the side-input / broadcast stream
> > > > 2. Using the OperatorCoordinator.
> > > >
> > > > Although we are having this discussion under the context of
> supporting
> > > CEP
> > > > dynamic pattern update, it would be really helpful to reach agreement
> > on
> > > > the design principle in general of how Flink should handle similar
> > > external
> > > > control demands, a.k.a how to provide a decent control plane in Flink
> > to
> > > > the users.
> > > >
> > > > Here is my take on these two options, based on the requirements of a
> > > > control plane.
> > > >
> > > > *Communication Requirements*
> > > > Flink has two kinds of control planes - in-band and out-of-band.
> > > > In-band control plane is like watermark and checkpoint marker. It
> > > requires
> > > > the entire DAG to be in a consistent state, so the control messages
> > flow
> > > > with the data in one direction. This is a one-way control flow.
> > > > Examples of out-of-band control plane is OC and JM/TM communication.
> > They
> > > > do not require a global consistency or awareness across the entire
> DAG.
> > > >
> > > > Before OC, neither of these two kinds of control plain was exposed to
> > the
> > > > users. OC allows the users to leverage the out-of-band control plane
> so
> > > > they can coordinate across subtasks. This is a more widely used
> control
> > > > flow from user defined operator perspective which requires 2-way
> > > > communication.
> > > >
> > > > - side-input stream is one-way communication. Moreover, I don't
> > think
> > > > iteration is the right way to address this. Unlike the abstraction
> > of
> > > > data
> > > > processing which is a DAG, the control plane may require
> > communication
> > > > between arbitrary two operators in different orders. Using
> > iterations
> > > > may
> > > > end up with an explosion of feedback edges that are not only
> > > > complicated to
> > > > express, but also hard to debug and maintain.
> > > > - OC provides a decent 2-way communication mechanism.
> > > >
> > > >
> > > > *Cost for low traffic use case*
> > > > An important difference between data channel and control channel is
> > > traffic
> > > > pattern. Unlike data plane, the control plane is usually idle for the
> > > vast
> > > > majority of the time with occasional control messages.
> > > >
> > > > - One argument to use the side-input / broadcast stream was that
> > users
> > > > can reuse the existing connectors. However, most Flink sources are
> > > > designed
> > > > to handle large throughput of traffic that maintains all the
> > threads,
> > > > network connections, etc. Not to say the external resources such
> as
> > > > Kafka
> > > > topics to store the commands.
> > > > - OC can have a much lower constant cost.
> > > >
> > > >
> > > > *Easy to use*
> > > > Personally speaking, I think the most simple and user-friendly
> > interface
> > > is
> > > > a REST API that accepts control commands.
> > > >
> > > > - One proposal at this point is to have a separate web server
> > > > independent of the Flink job. In that case, should users implement
> > > that
> > > > web
> > > > server? In order to pass the command to the Flink job, does that
> > mean
> > > > users
> > > > should implement a Flink source that can read the commands from
> the
> > > web
> > > > server? Or the web server would send the command to something like
> > > Kafka
> > > > and let the Flink side-input read from there. There seems to be a
> > lot
> > > > for
> > > > the users to do. And it seems an unnecessarily complicated system
> to
> > > > build
> > > > to send occasional control messages to a Flink job.
> > > > - OC can simply be reached via the JM REST API.
> > > > - e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > > > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx> would
> > simply
> > > > send the Content to the OC of OP_NAME.
> > > >
> > > > *Work well with checkpoints*
> > > >
> > > > - side-input streams works well with checkpoint, thanks to its
> > > > compatibility to the DAG abstraction.
> > > > - The OperatorCoordinator requires more careful design to work
> well
> > > with
> > > > checkpoints. The complexity mostly comes from the 2-way
> > communication.
> > > > At
> > > > this point the OperatorCoordinator message delivery semantic may
> not
> > > be
> > > > as
> > > > robust as side-input streams. However, I think this is mainly due
> to
> > > > potential bugs in implementation instead of fundamental design
> > > problems.
> > > > Basically the checkpoint semantic should be:
> > > > - The JM will first checkpoint all the OperatorCoordinator,
> more
> > > > specifically for each OperatorCoordinator,
> > > > - 1) JM blocks the input queue to stop receiving new events
> > from
> > > > the subtasks.
> > > > - 2) let all the operator coordinator finish processing all
> > the
> > > > pending events in the OC input queue.
> > > > - 3) flush the OC output queue until all the events sent are
> > > > acknowledged.
> > > > - 3) unblock the input queue, but block the output queue
> until
> > > all
> > > > the subtasks of the OC finish checkpoints.
> > > > - The JM starts a normal checkpoint starting from the Source.
> > > > - If an operator has a coordinator, and it has sent some
> > events
> > > to
> > > > the OC but has not been acknowledged. These events need to
> be
> > > > put into the
> > > > subtasks' checkpoint.
> > > > - After all the subtasks of an operator finishes checkpoint,
> the
> > > > output queue of the corresponding OC can be unblocked.
> > > > It looks that the above protocol would let OC have a clear
> > checkpoint
> > > > semantic. And this complexity seems must for 2-way communication.
> I
> > > > think
> > > > we are able to hide the above protocol from users by having an
> > > abstract
> > > > OC
> > > > implementation.
> > > >
> > > >
> > > > *Reprocess command history and repeatable processing results*
> > > > This seems not something generally required for a control plane. But
> if
> > > the
> > > > control plane changes the data processing behavior, there might be
> some
> > > use
> > > > case. Just like the CEP pattern update. In order to do this, users
> will
> > > > need to provide a full command history to the operators. That
> consists
> > of
> > > > two steps:
> > > >
> > > > 1. get the full command history. (Flink Source V.S. Custom way to
> > > > retrieve command history.)
> > > > 2. send them to the operators. (Side-input V.S. OC/Operator
> > > > communication)l
> > > >
> > > > I actually don't feel much difference between these two options. I am
> > not
> > > > sure if a Flink source is necessarily simpler than the user
> implemented
> > > > logic. For example, if all the changes are just written in a database
> > > > table. From the user's perspective, I feel fine with querying the DB
> by
> > > > myself using something like JDBC (or use KafkaConsumer to read the
> > > pattern
> > > > history from a Kafka topic) and send all the pattern change history
> to
> > > the
> > > > operators before they start to process the actual events.
> > > >
> > > > *Stability impact to the Flink Job*
> > > > I agree this is a valid concern. There is only one JM and currently
> OC
> > > runs
> > > > there, which may potentially cause JM crash and result in job
> failure.
> > > > Running in TM may have a less impact. So I think it makes sense to
> run
> > OC
> > > > in TM. However, this is more of how we can implement OC to make it
> more
> > > > robust. It does not forfeit the other semantic and user experience
> > > benefits
> > > > mentioned above.
> > > >
> > > >
> > > > To sum up:
> > > > 1. Regardless of whether CEP chooses OC or side-input stream, a
> decent
> > > > 2-way communication control plane seems really helpful and has been
> > > proven
> > > > by quite a few existing use cases. To me the question is how to make
> it
> > > > more robust, not whether we should use it or not.
> > > > 2. As for CEP, if we assume OC will be robust enough, personally I
> feel
> > > OC
> > > > is a better fit than side-input mainly because of the simplicity and
> > > > extensibility.
> > > >
> > > > Thanks,
> > > >
> > > > Jiangjie (Becket) Qin
> > > >
> > > >
> > > > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org>
> wrote:
> > > >
> > > > > Hi all,
> > > > >
> > > > > sorry for the late reply, vacation season ;) I'm still not 100%
> sold
> > on
> > > > > choosing the OC for this use-case, but on the other hand I don't
> have
> > > > > strong arguments against it. Few more questions / thoughts:
> > > > >
> > > > > We're still talking about the "web server based"
> > > > > pattern_processor_discoverer, but what about other use cases? One
> of
> > my
> > > > big
> > > > > concerns is that user's can not really reuse any part of the Flink
> > > > > ecosystem to implement the discovery logic. For example if they
> want
> > to
> > > > > read patterns from Kafka topic, they need to roll their own
> > discoverer
> > > > > based on the vanilla Kafka client. If we're talking about
> > > extensibility,
> > > > > should we also make sure that the existing primitives can be
> reused?
> > > > >
> > > > > For instance, the example I gave in my previous email seems not
> > easily
> > > > > > achievable with side-input / broadcast streams: a single invalid
> > > > pattern
> > > > > > detected on a TM can be disabled elegantly globally without
> > crashing
> > > > the
> > > > > > entire Flink job.
> > > > >
> > > > >
> > > > > This can be done for the side-input as well by filtering invalid
> > > patterns
> > > > > before the broadcast. You can also send the invalid patterns to any
> > > side
> > > > > output you want. I have a feeling that we're way too attached to
> the
> > > REST
> > > > > server use case in this discussion. I agree that for that case,
> this
> > > > > solution is the most straightforward one.
> > > > >
> > > > > OC is a 2-way communication mechanism, i.e. a subtask can also send
> > > > > > OperatorEvent to the coordinator to report its owns status, so
> that
> > > the
> > > > > > coordinator can act accordingly.
> > > > > >
> > > > >
> > > > > I agree that 2-way communication in the "data-flow like" API is
> > tricky,
> > > > > because it requires cycles / iterations, which are still not really
> > > > solved
> > > > > (for a good reason, it's really tough nut to crack). This makes me
> > > think
> > > > > that the OC may be bit of a "incomplete" workaround for not having
> > > fully
> > > > > working support for iterations.
> > > > >
> > > > > For example I'm not really confident that the checkpointing of the
> OC
> > > > works
> > > > > correctly right now, because it doesn't seem to require checkpoint
> > > > barrier
> > > > > alignment as the regular stream inputs. We also don't have a proper
> > > > support
> > > > > for watermarking (this is again tricky, because of the cycle).
> > > > >
> > > > > If we decide to go down this road, should we first address some of
> > > these
> > > > > limitations?
> > > > >
> > > > > OperatorCoordinator will checkpoint the full amount of
> > PatternProcessor
> > > > > > data. For the reprocessing of historical data, you can read the
> > > > > > PatternProcessor snapshots saved by this checkpoint from a
> certain
> > > > > > historical checkpoint, and then recreate the historical data
> > through
> > > > > these
> > > > > > PatternProcessor snapshots.
> > > > > >
> > > > >
> > > > > If I understand that correctly, this means only the LATEST state of
> > the
> > > > > patterns (in other words - patterns that are currently in use). Is
> > this
> > > > > really sufficient for historical re-processing? Can someone for
> > example
> > > > > want re-process the data in more of a "temporal join" fashion? Also
> > > AFAIK
> > > > > historical processing in combination with "coordinator checkpoints"
> > is
> > > > not
> > > > > really something that we currently support of the box, are there
> any
> > > > plans
> > > > > on tackling this (my other concern is that this should not go
> against
> > > the
> > > > > "unified batch & stream processing" efforts)?
> > > > >
> > > > > I do agree that having the user defined control logic defined in
> the
> > JM
> > > > > > increases the chance of instability.
> > > > > >
> > > > >
> > > > > I can imagine that if this should be a concern, we could move the
> > > > execution
> > > > > of the OC to the task managers. This also makes me thing, that we
> > > > shouldn't
> > > > > make any strong assumptions that the OC will always run in the
> > > JobManager
> > > > > (this is especially relevant for the embedded web-server use case).
> > > > >
> > > > > If an agreement is reached on OperatorCoodinator, I will start the
> > > voting
> > > > > > thread.
> > > > > >
> > > > >
> > > > > As for the vote, I'd would be great if we can wait until the next
> > week
> > > as
> > > > > many people took vacation until end of the year.
> > > > >
> > > > > Overall, I really like the feature, this will be a great addition
> to
> > > > Flink.
> > > > >
> > > > > Best,
> > > > > D.
> > > > >
> > > > >
> > > > >
> > > > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <
> > martijn@ververica.com
> > > >
> > > > > wrote:
> > > > >
> > > > > > Hi all,
> > > > > >
> > > > > > I can understand the need for a control plane mechanism. I'm not
> > the
> > > > > > technical go-to person for questions on the OperatorCoordinator,
> > but
> > > I
> > > > > > would expect that we could offer those interfaces from Flink but
> > > > > shouldn't
> > > > > > recommend running user-code in the JobManager itself. I think the
> > > user
> > > > > code
> > > > > > (like a webserver) should run outside of Flink (like via a
> sidecar)
> > > and
> > > > > use
> > > > > > only the provided interfaces to communicate.
> > > > > >
> > > > > > I would like to get @David Morávek <dm...@apache.org> opinion on
> > the
> > > > > > technical part.
> > > > > >
> > > > > > Best regards,
> > > > > >
> > > > > > Martijn
> > > > > >
> > > > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> > > nicholasjiang@apache.org
> > > > >
> > > > > > wrote:
> > > > > >
> > > > > >> Hi Konstantin, Becket, Martijn,
> > > > > >>
> > > > > >> Thanks for sharing your feedback. What other concerns do you
> have
> > > > about
> > > > > >> OperatorCoodinator? If an agreement is reached on
> > > OperatorCoodinator,
> > > > I
> > > > > >> will start the voting thread.
> > > > > >>
> > > > > >> Best,
> > > > > >> Nicholas Jiang
> > > > > >>
> > > > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > > > >> > Hi Konstantin,
> > > > > >> >
> > > > > >> > Thanks for sharing your thoughts. Please see the reply inline
> > > below.
> > > > > >> >
> > > > > >> > Thanks,
> > > > > >> >
> > > > > >> > Jiangjie (Becket) Qin
> > > > > >> >
> > > > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> > > knaufk@apache.org
> > > > >
> > > > > >> wrote:
> > > > > >> >
> > > > > >> > > Hi Becket, Hi Nicholas,
> > > > > >> > >
> > > > > >> > > Thanks for joining the discussion.
> > > > > >> > >
> > > > > >> > > 1 ) Personally, I would argue that we should only run user
> > code
> > > in
> > > > > the
> > > > > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems wrong
> to
> > > me
> > > > to
> > > > > >> > > encourage users to e.g. run a webserver on the Jobmanager,
> or
> > > > > >> continuously
> > > > > >> > > read patterns from a Kafka Topic on the Jobmanager, but both
> > of
> > > > > these
> > > > > >> I see
> > > > > >> > > happening with the current design. We've had lots of issues
> > with
> > > > > >> > > classloading leaks and other stability issues on the
> > Jobmanager
> > > > and
> > > > > >> making
> > > > > >> > > this more complicated, if there is another way, seems
> > > unnecessary.
> > > > > >> >
> > > > > >> >
> > > > > >> > I think the key question here is what primitive does Flink
> > provide
> > > > to
> > > > > >> > facilitate the user implementation of their own control logic
> /
> > > > > control
> > > > > >> > plane? It looks that previously, Flink assumes that all the
> user
> > > > logic
> > > > > >> is
> > > > > >> > just data processing logic without any control / coordination
> > > > > >> requirements.
> > > > > >> > However, it turns out that a decent control plane abstraction
> is
> > > > > >> required
> > > > > >> > in association with the data processing logic in many cases,
> > > > including
> > > > > >> > Source / Sink and other user defined operators in general. The
> > > fact
> > > > > >> that we
> > > > > >> > ended up with adding the SplitEnumerator and GlobalCommitter
> are
> > > > just
> > > > > >> two
> > > > > >> > examples of the demand of such coordination among user defined
> > > > logics.
> > > > > >> > There are other cases that we see in ecosystem projects, such
> as
> > > > > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > > > > >> >
> > > > > >> > Such control plane primitives are critical to the
> extensibility
> > > of a
> > > > > >> > project. If we look at other projects, exposing such control
> > plane
> > > > > >> logic is
> > > > > >> > quite common. For example, Hadoop ended up with exposing YARN
> > as a
> > > > > >> public
> > > > > >> > API to the users, which is extremely popular. Kafka consumers
> > > > exposed
> > > > > >> the
> > > > > >> > consumer group rebalance logic to the users via
> > > > > >> ConsumerPartitionAssigner,
> > > > > >> > which is also a control plane primitive.
> > > > > >> >
> > > > > >> > To me it is more important to think about how we can improve
> the
> > > > > >> stability
> > > > > >> > of such a control plane mechanism, instead of simply saying no
> > to
> > > > the
> > > > > >> users.
> > > > > >> >
> > > > > >> >
> > > > > >> >
> > > > > >> >
> > > > > >> > > 2) In addition, I suspect that, over time we will have to
> > > > implement
> > > > > >> all the
> > > > > >> > > functionality that regular sources already provide around
> > > > > consistency
> > > > > >> > > (watermarks, checkpointing) for the
> > PatternProcessorCoordinator,
> > > > > too.
> > > > > >> >
> > > > > >> >
> > > > > >> > I think OperatorCoordinator should have a generic
> communication
> > > > > >> mechanism
> > > > > >> > for all the operators, not specific to Source. We should
> > probably
> > > > have
> > > > > >> an
> > > > > >> > AbstractOperatorCoordinator help dealing with the
> communication
> > > > layer,
> > > > > >> and
> > > > > >> > leave the state maintenance and event handling logic to the
> user
> > > > code.
> > > > > >> >
> > > > > >> >
> > > > > >> > > 3) I understand that running on the Jobmanager is easier if
> > you
> > > > want
> > > > > >> to
> > > > > >> > > launch a REST server directly. Here my question would be:
> does
> > > > this
> > > > > >> really
> > > > > >> > > need to be solved inside of Flink or couldn't you start a
> > > > webserver
> > > > > >> next to
> > > > > >> > > Flink? If we start using the Jobmanager as a REST server
> users
> > > > will
> > > > > >> expect
> > > > > >> > > that e.g. it is highly available and can be load balanced
> and
> > we
> > > > > >> quickly
> > > > > >> > > need to think about aspects that we never wanted to think
> > about
> > > in
> > > > > the
> > > > > >> > > context of a Flink Jobmanager.
> > > > > >> > >
> > > > > >> >
> > > > > >> > I think the REST API is just for receiving commands targeting
> a
> > > > > running
> > > > > >> > Flink job. If the job fails, the REST API would be useless.
> > > > > >> >
> > > > > >> >
> > > > > >> > > So, can you elaborate a bit more, why a side-input/broadcast
> > > > stream
> > > > > is
> > > > > >> > >
> > > > > >> > > a) more difficult
> > > > > >> > > b) has vague semantics (To me semantics of a stream-stream
> > seem
> > > > > >> clearer
> > > > > >> > > when it comes to out-of-orderness, late data, reprocessing
> or
> > > > batch
> > > > > >> > > execution mode.)
> > > > > >> >
> > > > > >> >
> > > > > >> > I do agree that having the user defined control logic defined
> in
> > > the
> > > > > JM
> > > > > >> > increases the chance of instability. In that case, we may
> think
> > of
> > > > > other
> > > > > >> > solutions and I am fully open to that. But the side-input /
> > > > broadcast
> > > > > >> > stream seems more like a bandaid instead of a carefully
> designed
> > > > > control
> > > > > >> > plane mechanism.
> > > > > >> >
> > > > > >> > A decent control plane requires two-way communication, so
> > > > information
> > > > > >> can
> > > > > >> > be reported / collected from the entity being controlled, and
> > the
> > > > > >> > coordinator / controller can send decisions or commands to the
> > > > > entities
> > > > > >> > accordingly, just like our TM / JM communication. IIUC, this
> is
> > > not
> > > > > >> > achievable with the existing side-input / broadcast stream as
> > both
> > > > of
> > > > > >> them
> > > > > >> > are one-way communication mechanisms. For instance, the
> example
> > I
> > > > gave
> > > > > >> in
> > > > > >> > my previous email seems not easily achievable with side-input
> /
> > > > > >> broadcast
> > > > > >> > streams: a single invalid pattern detected on a TM can be
> > disabled
> > > > > >> > elegantly globally without crashing the entire Flink job.
> > > > > >> >
> > > > > >> >
> > > > > >> > > Cheers,
> > > > > >> > >
> > > > > >> > > Konstantin
> > > > > >> > >
> > > > > >> > >
> > > > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> > > becket.qin@gmail.com
> > > > >
> > > > > >> wrote:
> > > > > >> > >
> > > > > >> > > > Hi folks,
> > > > > >> > > >
> > > > > >> > > > I just finished reading the previous emails. It was a good
> > > > > >> discussion.
> > > > > >> > > Here
> > > > > >> > > > are my two cents:
> > > > > >> > > >
> > > > > >> > > > *Is OperatorCoordinator a public API?*
> > > > > >> > > > Regarding the OperatorCoordinator, although it is marked
> as
> > > > > internal
> > > > > >> > > > interface at this point, I intended to make it a public
> > > > interface
> > > > > >> when
> > > > > >> > > add
> > > > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> > > communication
> > > > > >> mechanism
> > > > > >> > > > that enables many use cases, Source / Sink / TF on Flink /
> > CEP
> > > > > here
> > > > > >> > > again.
> > > > > >> > > > To my understanding, OC was marked as internal because we
> > > think
> > > > it
> > > > > >> is not
> > > > > >> > > > stable enough yet. We may need to fortify the
> OperatorEvent
> > > > > delivery
> > > > > >> > > > semantic a little bit so it works well with checkpoint in
> > > > general.
> > > > > >> > > >
> > > > > >> > > > I think it is a valid concern that user code running in JM
> > may
> > > > > cause
> > > > > >> > > > instability. However, not providing this communication
> > > mechanism
> > > > > >> only
> > > > > >> > > makes
> > > > > >> > > > a lot of use case even harder to implement. So it seems
> that
> > > > > having
> > > > > >> the
> > > > > >> > > OC
> > > > > >> > > > exposed to end users brings more benefits than harm to
> > Flink.
> > > At
> > > > > >> the end
> > > > > >> > > of
> > > > > >> > > > the day, users have many ways to crash a Flink job if they
> > do
> > > > not
> > > > > >> write
> > > > > >> > > > proper code. So making those who know what they do happy
> > seems
> > > > > more
> > > > > >> > > > important here.
> > > > > >> > > >
> > > > > >> > > > *OperatorCoordinator V.S. side-input / broadcast stream*
> > > > > >> > > > I think both of them can achieve the goal of dynamic
> > patterns.
> > > > The
> > > > > >> main
> > > > > >> > > > difference is the extensibility.
> > > > > >> > > >
> > > > > >> > > > OC is a 2-way communication mechanism, i.e. a subtask can
> > also
> > > > > send
> > > > > >> > > > OperatorEvent to the coordinator to report its owns
> status,
> > so
> > > > > that
> > > > > >> the
> > > > > >> > > > coordinator can act accordingly. This is sometimes useful.
> > For
> > > > > >> example, a
> > > > > >> > > > single invalid pattern can be disabled elegantly without
> > > > crashing
> > > > > >> the
> > > > > >> > > > entire Flink job. In the future, if we allow users to send
> > > > > external
> > > > > >> > > command
> > > > > >> > > > to OC via JM, a default self-contained implementation can
> > just
> > > > > >> update the
> > > > > >> > > > pattern via the REST API without external dependencies.
> > > > > >> > > >
> > > > > >> > > > Another reason I personally prefer OC is because it is an
> > > > explicit
> > > > > >> > > control
> > > > > >> > > > plain mechanism, where as the side-input / broadcast
> stream
> > > has
> > > > > are
> > > > > >> more
> > > > > >> > > > vague semantic.
> > > > > >> > > >
> > > > > >> > > > Thanks,
> > > > > >> > > >
> > > > > >> > > > Jiangjie (Becket) Qin
> > > > > >> > > >
> > > > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> > > dmvk@apache.org>
> > > > > >> wrote:
> > > > > >> > > >
> > > > > >> > > > > Hi Yunfeng,
> > > > > >> > > > >
> > > > > >> > > > > thanks for drafting this FLIP, this will be a great
> > addition
> > > > > into
> > > > > >> the
> > > > > >> > > CEP
> > > > > >> > > > > toolbox!
> > > > > >> > > > >
> > > > > >> > > > > Apart from running user code in JM, which want to avoid
> in
> > > > > >> general, I'd
> > > > > >> > > > > have one more another concern about using the
> > > > > OperatorCoordinator
> > > > > >> and
> > > > > >> > > > that
> > > > > >> > > > > is re-processing of the historical data. Any thoughts
> > about
> > > > how
> > > > > >> this
> > > > > >> > > will
> > > > > >> > > > > work with the OC?
> > > > > >> > > > >
> > > > > >> > > > > I have a slight feeling that a side-input (custom
> source /
> > > > > >> operator +
> > > > > >> > > > > broadcast) would a better fit for this case. This would
> > > > simplify
> > > > > >> the
> > > > > >> > > > > consistency concerns (watermarks + pushback) and the
> > > > > >> re-processing of
> > > > > >> > > > > historical data.
> > > > > >> > > > >
> > > > > >> > > > > Best,
> > > > > >> > > > > D.
> > > > > >> > > > >
> > > > > >> > > > >
> > > > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > > > >> > > nicholasjiang@apache.org
> > > > > >> > > > >
> > > > > >> > > > > wrote:
> > > > > >> > > > >
> > > > > >> > > > > > Hi Konstantin, Martijn
> > > > > >> > > > > >
> > > > > >> > > > > > Thanks for the detailed feedback in the discussion.
> > What I
> > > > > >> still have
> > > > > >> > > > > left
> > > > > >> > > > > > to answer/reply to:
> > > > > >> > > > > >
> > > > > >> > > > > > -- Martijn: Just to be sure, this indeed would mean
> that
> > > if
> > > > > for
> > > > > >> > > > whatever
> > > > > >> > > > > > reason the heartbeat timeout, it would crash the job,
> > > right?
> > > > > >> > > > > >
> > > > > >> > > > > > IMO, if for whatever reason the heartbeat timeout, it
> > > > couldn't
> > > > > >> check
> > > > > >> > > > the
> > > > > >> > > > > > PatternProcessor consistency between the
> > > OperatorCoordinator
> > > > > >> and the
> > > > > >> > > > > > subtasks so that the job would be crashed.
> > > > > >> > > > > >
> > > > > >> > > > > > -- Konstantin: What I was concerned about is that we
> > > > basically
> > > > > >> let
> > > > > >> > > > users
> > > > > >> > > > > > run a UserFunction in the OperatorCoordinator, which
> it
> > > does
> > > > > >> not seem
> > > > > >> > > > to
> > > > > >> > > > > > have been designed for.
> > > > > >> > > > > >
> > > > > >> > > > > > In general, we have reached an agreement on the design
> > of
> > > > this
> > > > > >> FLIP,
> > > > > >> > > > but
> > > > > >> > > > > > there are some concerns on the OperatorCoordinator,
> > about
> > > > > >> whether
> > > > > >> > > > > basically
> > > > > >> > > > > > let users run a UserFunction in the
> OperatorCoordinator
> > is
> > > > > >> designed
> > > > > >> > > for
> > > > > >> > > > > > OperatorCoordinator. We would like to invite Becket
> Qin
> > > who
> > > > is
> > > > > >> the
> > > > > >> > > > author
> > > > > >> > > > > > of OperatorCoordinator to help us to answer this
> > concern.
> > > > > >> > > > > >
> > > > > >> > > > > > Best,
> > > > > >> > > > > > Nicholas Jiang
> > > > > >> > > > > >
> > > > > >> > > > > >
> > > > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > > > >> > > > > > > Hi all,
> > > > > >> > > > > > >
> > > > > >> > > > > > > Really like the discussion on this topic moving
> > > forward. I
> > > > > >> really
> > > > > >> > > > think
> > > > > >> > > > > > > this feature will be much appreciated by the Flink
> > > users.
> > > > > >> What I
> > > > > >> > > > still
> > > > > >> > > > > > have
> > > > > >> > > > > > > left to answer/reply to:
> > > > > >> > > > > > >
> > > > > >> > > > > > > -- Good point. If for whatever reason the different
> > > > > >> taskmanagers
> > > > > >> > > > can't
> > > > > >> > > > > > get
> > > > > >> > > > > > > the latest rule, the Operator Coordinator could
> send a
> > > > > >> heartbeat to
> > > > > >> > > > all
> > > > > >> > > > > > > taskmanagers with the latest rules and check the
> > > heartbeat
> > > > > >> response
> > > > > >> > > > > from
> > > > > >> > > > > > > all the taskmanagers whether the latest rules of the
> > > > > >> taskmanager is
> > > > > >> > > > > equal
> > > > > >> > > > > > > to these of the Operator Coordinator.
> > > > > >> > > > > > >
> > > > > >> > > > > > > Just to be sure, this indeed would mean that if for
> > > > whatever
> > > > > >> reason
> > > > > >> > > > the
> > > > > >> > > > > > > heartbeat timeout, it would crash the job, right?
> > > > > >> > > > > > >
> > > > > >> > > > > > > -- We have consided about the solution mentioned
> > above.
> > > In
> > > > > >> this
> > > > > >> > > > > > solution, I
> > > > > >> > > > > > > have some questions about how to guarantee the
> > > consistency
> > > > > of
> > > > > >> the
> > > > > >> > > > rule
> > > > > >> > > > > > > between each TaskManager. By having a coodinator in
> > the
> > > > > >> JobManager
> > > > > >> > > to
> > > > > >> > > > > > > centrally manage the latest rules, the latest rules
> of
> > > all
> > > > > >> > > > TaskManagers
> > > > > >> > > > > > are
> > > > > >> > > > > > > consistent with those of the JobManager, so as to
> > avoid
> > > > the
> > > > > >> > > > > > inconsistencies
> > > > > >> > > > > > > that may be encountered in the above solution. Can
> you
> > > > > >> introduce
> > > > > >> > > how
> > > > > >> > > > > this
> > > > > >> > > > > > > solution guarantees the consistency of the rules?
> > > > > >> > > > > > >
> > > > > >> > > > > > > The consistency that we could guarantee was based on
> > how
> > > > > >> often each
> > > > > >> > > > > > > TaskManager would do a refresh and how often we
> would
> > > > > accept a
> > > > > >> > > > refresh
> > > > > >> > > > > to
> > > > > >> > > > > > > fail. We set the refresh time to a relatively short
> > one
> > > > (30
> > > > > >> > > seconds)
> > > > > >> > > > > and
> > > > > >> > > > > > > maximum failures to 3. That meant that we could
> > > guarantee
> > > > > that
> > > > > >> > > rules
> > > > > >> > > > > > would
> > > > > >> > > > > > > be updated in < 2 minutes or else the job would
> crash.
> > > > That
> > > > > >> was
> > > > > >> > > > > > sufficient
> > > > > >> > > > > > > for our use cases. This also really depends on how
> big
> > > > your
> > > > > >> cluster
> > > > > >> > > > > is. I
> > > > > >> > > > > > > can imagine that if you have a large scale cluster
> > that
> > > > you
> > > > > >> want to
> > > > > >> > > > > run,
> > > > > >> > > > > > > you don't want to DDOS the backend system where you
> > have
> > > > > your
> > > > > >> rules
> > > > > >> > > > > > stored.
> > > > > >> > > > > > >
> > > > > >> > > > > > > -- In summary, the current design is that JobManager
> > > tells
> > > > > all
> > > > > >> > > > > > TaskManagers
> > > > > >> > > > > > > the latest rules through OperatorCoodinator, and
> will
> > > > > >> initiate a
> > > > > >> > > > > > heartbeat
> > > > > >> > > > > > > to check whether the latest rules on each
> TaskManager
> > > are
> > > > > >> > > consistent.
> > > > > >> > > > > We
> > > > > >> > > > > > > will describe how to deal with the Failover scenario
> > in
> > > > more
> > > > > >> detail
> > > > > >> > > > on
> > > > > >> > > > > > FLIP.
> > > > > >> > > > > > >
> > > > > >> > > > > > > Thanks for that. I think having the JobManager tell
> > the
> > > > > >> > > TaskManagers
> > > > > >> > > > > the
> > > > > >> > > > > > > applicable rules would indeed end up being the best
> > > > design.
> > > > > >> > > > > > >
> > > > > >> > > > > > > -- about the concerns around consistency raised by
> > > > Martijn:
> > > > > I
> > > > > >> > > think a
> > > > > >> > > > > lot
> > > > > >> > > > > > > of those can be mitigated by using an event time
> > > timestamp
> > > > > >> from
> > > > > >> > > which
> > > > > >> > > > > the
> > > > > >> > > > > > > rules take effect. The reprocessing scenario, for
> > > example,
> > > > > is
> > > > > >> > > covered
> > > > > >> > > > > by
> > > > > >> > > > > > > this. If a pattern processor should become active as
> > > soon
> > > > as
> > > > > >> > > > possible,
> > > > > >> > > > > > > there will still be inconsistencies between
> > > Taskmanagers,
> > > > > but
> > > > > >> "as
> > > > > >> > > > soon
> > > > > >> > > > > as
> > > > > >> > > > > > > possible" is vague anyway, which is why I think
> that's
> > > ok.
> > > > > >> > > > > > >
> > > > > >> > > > > > > I think an event timestamp is indeed a really
> > important
> > > > one.
> > > > > >> We
> > > > > >> > > also
> > > > > >> > > > > used
> > > > > >> > > > > > > that in my previous role, with the
> > > ruleActivationTimestamp
> > > > > >> compared
> > > > > >> > > > to
> > > > > >> > > > > > > eventtime (well, actually we used Kafka logAppend
> time
> > > > > because
> > > > > >> > > > > > > eventtime wasn't always properly set so we used that
> > > time
> > > > to
> > > > > >> > > > overwrite
> > > > > >> > > > > > the
> > > > > >> > > > > > > eventtime from the event itself).
> > > > > >> > > > > > >
> > > > > >> > > > > > > Best regards,
> > > > > >> > > > > > >
> > > > > >> > > > > > > Martijn
> > > > > >> > > > > > >
> > > > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> > > > > >> knaufk@apache.org>
> > > > > >> > > > > > wrote:
> > > > > >> > > > > > >
> > > > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > about the concerns around consistency raised by
> > > > Martijn: I
> > > > > >> think
> > > > > >> > > a
> > > > > >> > > > > lot
> > > > > >> > > > > > of
> > > > > >> > > > > > > > those can be mitigated by using an event time
> > > timestamp
> > > > > from
> > > > > >> > > which
> > > > > >> > > > > the
> > > > > >> > > > > > > > rules take effect. The reprocessing scenario, for
> > > > example,
> > > > > >> is
> > > > > >> > > > covered
> > > > > >> > > > > > by
> > > > > >> > > > > > > > this. If a pattern processor should become active
> as
> > > > soon
> > > > > as
> > > > > >> > > > > possible,
> > > > > >> > > > > > > > there will still be inconsistencies between
> > > > Taskmanagers,
> > > > > >> but "as
> > > > > >> > > > > soon
> > > > > >> > > > > > as
> > > > > >> > > > > > > > possible" is vague anyway, which is why I think
> > that's
> > > > ok.
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > about naming: The naming with "PatternProcessor"
> > > sounds
> > > > > >> good to
> > > > > >> > > me.
> > > > > >> > > > > > Final
> > > > > >> > > > > > > > nit: I would go for CEP#patternProccessors, which
> > > would
> > > > be
> > > > > >> > > > consistent
> > > > > >> > > > > > with
> > > > > >> > > > > > > > CEP#pattern.
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > I am not sure about one of the rejected
> > alternatives:
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > > Have each subtask of an operator make the update
> > on
> > > > > their
> > > > > >> own
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > -
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > It is hard to achieve consistency.
> > > > > >> > > > > > > > -
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > Though the time interval that each subtask
> > makes
> > > > the
> > > > > >> update
> > > > > >> > > > can
> > > > > >> > > > > > be
> > > > > >> > > > > > > > the same, the absolute time they make the
> > update
> > > > > >> might be
> > > > > >> > > > > > different.
> > > > > >> > > > > > > > For
> > > > > >> > > > > > > > example, one makes updates at 10:00, 10:05,
> > etc,
> > > > > while
> > > > > >> > > > another
> > > > > >> > > > > > does
> > > > > >> > > > > > > > it at
> > > > > >> > > > > > > > 10:01, 10:06. In this case the subtasks
> might
> > > > never
> > > > > >> > > > processing
> > > > > >> > > > > > data
> > > > > >> > > > > > > > with
> > > > > >> > > > > > > > the same set of pattern processors.
> > > > > >> > > > > > > >
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > I would have thought that it is quite easy to poll
> > for
> > > > the
> > > > > >> rules
> > > > > >> > > > from
> > > > > >> > > > > > each
> > > > > >> > > > > > > > Subtask at *about *the same time. So, this alone
> > does
> > > > not
> > > > > >> seem to
> > > > > >> > > > be
> > > > > >> > > > > > > > enough to rule out this option. I've looped in
> David
> > > > > >> Moravek to
> > > > > >> > > get
> > > > > >> > > > > his
> > > > > >> > > > > > > > opinion of the additional load imposed on the JM.
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > Thanks,
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > Konstantin
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas Jiang <
> > > > > >> > > > > > nicholasjiang@apache.org>
> > > > > >> > > > > > > > wrote:
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > > Hi Yue,
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > Thanks for your feedback of the FLIP. I have
> > > addressed
> > > > > >> your
> > > > > >> > > > > > questions and
> > > > > >> > > > > > > > > made a corresponding explanation as follows:
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > > > >> > > PatternProcessoerDiscoverer
> > > > > >> > > > to
> > > > > >> > > > > > > > update
> > > > > >> > > > > > > > > the rules, will it increase the load of JM? For
> > > > example,
> > > > > >> if the
> > > > > >> > > > > user
> > > > > >> > > > > > > > wants
> > > > > >> > > > > > > > > the updated rule to take effect immediately,,
> > which
> > > > > means
> > > > > >> that
> > > > > >> > > we
> > > > > >> > > > > > need to
> > > > > >> > > > > > > > > set a shorter check interval or there is another
> > > > > scenario
> > > > > >> when
> > > > > >> > > > > users
> > > > > >> > > > > > > > rarely
> > > > > >> > > > > > > > > update the pattern, will the
> > > > PatternProcessoerDiscoverer
> > > > > >> be in
> > > > > >> > > > most
> > > > > >> > > > > > of
> > > > > >> > > > > > > > the
> > > > > >> > > > > > > > > time Do useless checks ? Will a lazy update mode
> > > could
> > > > > be
> > > > > >> used,
> > > > > >> > > > > > which the
> > > > > >> > > > > > > > > pattern only be updated when triggered by the
> > user,
> > > > and
> > > > > do
> > > > > >> > > > nothing
> > > > > >> > > > > at
> > > > > >> > > > > > > > other
> > > > > >> > > > > > > > > times?
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > PatternProcessoerDiscoverer is a user-defined
> > > > interface
> > > > > to
> > > > > >> > > > discover
> > > > > >> > > > > > the
> > > > > >> > > > > > > > > PatternProcessor updates. Periodically checking
> > the
> > > > > >> > > > > PatternProcessor
> > > > > >> > > > > > in
> > > > > >> > > > > > > > the
> > > > > >> > > > > > > > > database is a implementation of the
> > > > > >> PatternProcessoerDiscoverer
> > > > > >> > > > > > > > interface,
> > > > > >> > > > > > > > > which is that periodically querys all the
> > > > > PatternProcessor
> > > > > >> > > table
> > > > > >> > > > in
> > > > > >> > > > > > > > certain
> > > > > >> > > > > > > > > interval. This implementation indeeds has the
> > > useless
> > > > > >> checks,
> > > > > >> > > and
> > > > > >> > > > > > could
> > > > > >> > > > > > > > > directly integrates the changelog of the table.
> In
> > > > > >> addition, in
> > > > > >> > > > > > addition
> > > > > >> > > > > > > > to
> > > > > >> > > > > > > > > the implementation of periodically checking the
> > > > > database,
> > > > > >> there
> > > > > >> > > > are
> > > > > >> > > > > > other
> > > > > >> > > > > > > > > implementations such as the PatternProcessor
> that
> > > > > provides
> > > > > >> > > > Restful
> > > > > >> > > > > > > > services
> > > > > >> > > > > > > > > to receive updates.
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > -- I still have some confusion about how Key
> > > > Generating
> > > > > >> > > > Opertator
> > > > > >> > > > > > and
> > > > > >> > > > > > > > > CepOperator (Pattern Matching & Processing
> > Operator)
> > > > > work
> > > > > >> > > > together.
> > > > > >> > > > > > If
> > > > > >> > > > > > > > > there are N PatternProcessors, will the Key
> > > Generating
> > > > > >> > > Opertator
> > > > > >> > > > > > > > generate N
> > > > > >> > > > > > > > > keyedStreams, and then N CepOperator would
> process
> > > > each
> > > > > >> Key
> > > > > >> > > > > > separately ?
> > > > > >> > > > > > > > Or
> > > > > >> > > > > > > > > every CepOperator Task would process all
> patterns,
> > > if
> > > > > so,
> > > > > >> does
> > > > > >> > > > the
> > > > > >> > > > > > key
> > > > > >> > > > > > > > type
> > > > > >> > > > > > > > > in each PatternProcessor need to be the same?
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > Firstly the Pattern Matching & Processing
> Operator
> > > is
> > > > > not
> > > > > >> the
> > > > > >> > > > > > CepOperator
> > > > > >> > > > > > > > > at present, because CepOperator mechanism is
> based
> > > on
> > > > > the
> > > > > >> > > > NFAState.
> > > > > >> > > > > > > > > Secondly if there are N PatternProcessors, the
> Key
> > > > > >> Generating
> > > > > >> > > > > > Opertator
> > > > > >> > > > > > > > > combines all the keyedStreams with keyBy()
> > > operation,
> > > > > >> thus the
> > > > > >> > > > > > Pattern
> > > > > >> > > > > > > > > Matching & Processing Operator would process all
> > the
> > > > > >> patterns.
> > > > > >> > > In
> > > > > >> > > > > > other
> > > > > >> > > > > > > > > words, the KeySelector of the PatternProcessor
> is
> > > used
> > > > > >> for the
> > > > > >> > > > Key
> > > > > >> > > > > > > > > Generating Opertator, and the Pattern and
> > > > > >> > > PatternProceessFunction
> > > > > >> > > > > of
> > > > > >> > > > > > the
> > > > > >> > > > > > > > > PatternProcessor are used for the Pattern
> > Matching &
> > > > > >> Processing
> > > > > >> > > > > > Operator.
> > > > > >> > > > > > > > > Lastly the key type in each PatternProcessor is
> > the
> > > > > same,
> > > > > >> > > > regarded
> > > > > >> > > > > as
> > > > > >> > > > > > > > > Object type.
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > -- Maybe need to pay attention to it when
> > > implementing
> > > > > it
> > > > > >> .If
> > > > > >> > > > some
> > > > > >> > > > > > > > Pattern
> > > > > >> > > > > > > > > has been removed or updated, will the partially
> > > > matched
> > > > > >> results
> > > > > >> > > > in
> > > > > >> > > > > > > > > StateBackend would be clean up or We rely on
> state
> > > ttl
> > > > > to
> > > > > >> clean
> > > > > >> > > > up
> > > > > >> > > > > > these
> > > > > >> > > > > > > > > expired states.
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > If certain Pattern has been removed or updated,
> > the
> > > > > >> partially
> > > > > >> > > > > matched
> > > > > >> > > > > > > > > results in StateBackend would be clean up until
> > the
> > > > next
> > > > > >> > > > > checkpoint.
> > > > > >> > > > > > The
> > > > > >> > > > > > > > > partially matched result doesn't depend on the
> > state
> > > > ttl
> > > > > >> of the
> > > > > >> > > > > > > > > StateBackend.
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > 4. Will the PatternProcessorManager keep all the
> > > > active
> > > > > >> > > > > > PatternProcessor
> > > > > >> > > > > > > > > in memory? We have also Support Multiple Rule
> and
> > > > > Dynamic
> > > > > >> Rule
> > > > > >> > > > > > Changing.
> > > > > >> > > > > > > > > But we are facing such a problem, some users’
> > usage
> > > > > >> scenarios
> > > > > >> > > are
> > > > > >> > > > > > that
> > > > > >> > > > > > > > they
> > > > > >> > > > > > > > > want to have their own pattern for each user_id,
> > > which
> > > > > >> means
> > > > > >> > > that
> > > > > >> > > > > > there
> > > > > >> > > > > > > > > could be thousands of patterns, which would make
> > the
> > > > > >> > > performance
> > > > > >> > > > of
> > > > > >> > > > > > > > Pattern
> > > > > >> > > > > > > > > Matching very poor. We are also trying to solve
> > this
> > > > > >> problem.
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > The PatternProcessorManager keeps all the active
> > > > > >> > > PatternProcessor
> > > > > >> > > > > in
> > > > > >> > > > > > > > > memory. For scenarios that they want to have
> their
> > > own
> > > > > >> pattern
> > > > > >> > > > for
> > > > > >> > > > > > each
> > > > > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> > > > fine-grained
> > > > > >> pattern
> > > > > >> > > > of
> > > > > >> > > > > > > > > PatternProcessor to solve the performance
> problem
> > of
> > > > the
> > > > > >> > > Pattern
> > > > > >> > > > > > > > Matching,
> > > > > >> > > > > > > > > for example, a pattern corresponds to a group of
> > > > users?
> > > > > >> The
> > > > > >> > > > > scenarios
> > > > > >> > > > > > > > > mentioned above need to be solved by case by
> case.
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > Best,
> > > > > >> > > > > > > > > Nicholas Jiang
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > > > >> > > > > > > > > > Glad to see the Community's progress in Flink
> > CEP.
> > > > > After
> > > > > >> > > > reading
> > > > > >> > > > > > this
> > > > > >> > > > > > > > > Flip,
> > > > > >> > > > > > > > > > I have few questions, would you please take a
> > look
> > > > ?
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > > > >> > > > PatternProcessoerDiscoverer
> > > > > >> > > > > to
> > > > > >> > > > > > > > > update
> > > > > >> > > > > > > > > > the rules, will it increase the load of JM?
> For
> > > > > >> example, if
> > > > > >> > > the
> > > > > >> > > > > > user
> > > > > >> > > > > > > > > wants
> > > > > >> > > > > > > > > > the updated rule to take effect immediately,,
> > > which
> > > > > >> means
> > > > > >> > > that
> > > > > >> > > > we
> > > > > >> > > > > > need
> > > > > >> > > > > > > > to
> > > > > >> > > > > > > > > > set a shorter check interval or there is
> > another
> > > > > >> scenario
> > > > > >> > > when
> > > > > >> > > > > > users
> > > > > >> > > > > > > > > > rarely update the pattern, will the
> > > > > >> > > PatternProcessoerDiscoverer
> > > > > >> > > > > be
> > > > > >> > > > > > in
> > > > > >> > > > > > > > > most
> > > > > >> > > > > > > > > > of the time Do useless checks ? Will a lazy
> > update
> > > > > mode
> > > > > >> could
> > > > > >> > > > be
> > > > > >> > > > > > used,
> > > > > >> > > > > > > > > > which the pattern only be updated when
> triggered
> > > by
> > > > > the
> > > > > >> user,
> > > > > >> > > > and
> > > > > >> > > > > > do
> > > > > >> > > > > > > > > > nothing at other times ?
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > > > 2. I still have some confusion about how Key
> > > > > >> Generating
> > > > > >> > > > > > Opertator and
> > > > > >> > > > > > > > > > CepOperator (Pattern Matching & Processing
> > > Operator)
> > > > > >> work
> > > > > >> > > > > > together. If
> > > > > >> > > > > > > > > > there are N PatternProcessors, will the Key
> > > > Generating
> > > > > >> > > > Opertator
> > > > > >> > > > > > > > > generate N
> > > > > >> > > > > > > > > > keyedStreams, and then N CepOperator would
> > process
> > > > > each
> > > > > >> Key
> > > > > >> > > > > > separately
> > > > > >> > > > > > > > ?
> > > > > >> > > > > > > > > Or
> > > > > >> > > > > > > > > > every CepOperator Task would process all
> > patterns,
> > > > if
> > > > > >> so,
> > > > > >> > > does
> > > > > >> > > > > the
> > > > > >> > > > > > key
> > > > > >> > > > > > > > > type
> > > > > >> > > > > > > > > > in each PatternProcessor need to be the same ?
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > > > 3. Maybe need to pay attention to it when
> > > > implementing
> > > > > >> it .If
> > > > > >> > > > > some
> > > > > >> > > > > > > > > Pattern
> > > > > >> > > > > > > > > > has been removed or updateed ,will the
> > partially
> > > > > >> matched
> > > > > >> > > > results
> > > > > >> > > > > > in
> > > > > >> > > > > > > > > > StateBackend would be clean up or We rely on
> > state
> > > > ttl
> > > > > >> to
> > > > > >> > > clean
> > > > > >> > > > > up
> > > > > >> > > > > > > > these
> > > > > >> > > > > > > > > > expired states.
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > > > 4. Will the PatternProcessorManager keep all
> the
> > > > > active
> > > > > >> > > > > > > > PatternProcessor
> > > > > >> > > > > > > > > in
> > > > > >> > > > > > > > > > memory ? We have also Support Multiple Rule
> and
> > > > > Dynamic
> > > > > >> Rule
> > > > > >> > > > > > Changing .
> > > > > >> > > > > > > > > > But we are facing such a problem, some users’
> > > usage
> > > > > >> scenarios
> > > > > >> > > > are
> > > > > >> > > > > > that
> > > > > >> > > > > > > > > they
> > > > > >> > > > > > > > > > want to have their own pattern for each
> user_id,
> > > > which
> > > > > >> means
> > > > > >> > > > that
> > > > > >> > > > > > there
> > > > > >> > > > > > > > > > could be thousands of patterns, which would
> make
> > > the
> > > > > >> > > > performance
> > > > > >> > > > > of
> > > > > >> > > > > > > > > Pattern
> > > > > >> > > > > > > > > > Matching very poor. We are also trying to
> solve
> > > this
> > > > > >> problem.
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > > > Yunfeng Zhou <fl...@gmail.com>
> > > > > >> 于2021年12月10日周五
> > > > > >> > > > > 19:16写道：
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > > > > Hi all，
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > > > I'm opening this thread to propose the
> design
> > to
> > > > > >> support
> > > > > >> > > > > multiple
> > > > > >> > > > > > > > rule
> > > > > >> > > > > > > > > &
> > > > > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP
> > project,
> > > as
> > > > > >> > > described
> > > > > >> > > > in
> > > > > >> > > > > > > > > FLIP-200
> > > > > >> > > > > > > > > > > [1]
> > > > > >> > > > > > > > > > > .
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > > > Currently Flink CEP only supports having a
> > > single
> > > > > >> pattern
> > > > > >> > > > > inside
> > > > > >> > > > > > a
> > > > > >> > > > > > > > > > > CepOperator and does not support changing
> the
> > > > > pattern
> > > > > >> > > > > > dynamically. In
> > > > > >> > > > > > > > > order
> > > > > >> > > > > > > > > > > to reduce resource consumption and to
> > experience
> > > > > >> shorter
> > > > > >> > > > > downtime
> > > > > >> > > > > > > > > during
> > > > > >> > > > > > > > > > > pattern updates, there is a growing need in
> > the
> > > > > >> production
> > > > > >> > > > > > > > environment
> > > > > >> > > > > > > > > that
> > > > > >> > > > > > > > > > > expects CEP to support having multiple
> > patterns
> > > in
> > > > > one
> > > > > >> > > > operator
> > > > > >> > > > > > and
> > > > > >> > > > > > > > to
> > > > > >> > > > > > > > > > > support dynamically changing them.
> Therefore I
> > > > > >> propose to
> > > > > >> > > add
> > > > > >> > > > > > certain
> > > > > >> > > > > > > > > > > infrastructure as described in FLIP-200 to
> > > support
> > > > > >> these
> > > > > >> > > > > > > > > functionalities.
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > > > Please feel free to reply to this email
> > thread.
> > > > > >> Looking
> > > > > >> > > > forward
> > > > > >> > > > > > to
> > > > > >> > > > > > > > your
> > > > > >> > > > > > > > > > > feedback!
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > > > [1]
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > >
> > > > > >> > > > > >
> > > > > >> > > > >
> > > > > >> > > >
> > > > > >> > >
> > > > > >>
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > > > Best regards,
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > > > Yunfeng
> > > > > >> > > > > > > > > > >
> > > > > >> > > > > > > > > >
> > > > > >> > > > > > > > >
> > > > > >> > > > > > > >
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > --
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > Konstantin Knauf
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > https://twitter.com/snntrable
> > > > > >> > > > > > > >
> > > > > >> > > > > > > > https://github.com/knaufk
> > > > > >> > > > > > > >
> > > > > >> > > > > > >
> > > > > >> > > > > >
> > > > > >> > > > >
> > > > > >> > > >
> > > > > >> > >
> > > > > >> > >
> > > > > >> > > --
> > > > > >> > >
> > > > > >> > > Konstantin Knauf
> > > > > >> > >
> > > > > >> > > https://twitter.com/snntrable
> > > > > >> > >
> > > > > >> > > https://github.com/knaufk
> > > > > >> > >
> > > > > >> >
> > > > > >>
> > > > > >
> > > > >
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Till Rohrmann <tr...@apache.org>.
Thanks for the detailed explanation Becket.
Do you think that an additional dependency is a deal breaker for people to
use dynamic CEP patterns? At the very least people have to operate some
kind of storage/queue system from which the CEP job can read anyway. Maybe
it could be good enough to provide a REST endpoint (as a separate tool)
that can be instantiated with a Flink sink to ingest REST requests
into some queue. A general concern I have is that by making the JM a REST
ingestion point for data will push another responsibility to Flink and
increase the surface area further.
For how to handle data that cannot be processed by patterns, I think there
also exist other solutions. I could imagine that users could define
different failover strategies. E.g. one could simply ignore the record, the
pattern could get deactivated on the affected TM or the processing fails.
Maybe we are coupling the dynamic CEP pattern effort too much on where the
new patterns come from. Maybe we can split these efforts into supporting
dynamic CEP patterns on the TM reading from some source and then fork off
the discussion about introducing a user controlled control plane to Flink.
That way we wouldn't block this effort and could discuss more about the
exact properties such a user control plane would need to have. What do you
think?
Cheers,
Till
On Wed, Jan 5, 2022 at 7:18 AM Becket Qin <be...@gmail.com> wrote:
> Hi Till,
>
> Thanks for the comments and questions. To be clear, I am not saying that
> the side-input stream does not work for the dynamic pattern update use
> case. But I think OC is a better solution. The design goal for CEP dynamic
> pattern is not only make it work, but also make it user friendly and
> extensible. So as a user, I expect the following:
>
> - Use CEP with dynamic pattern update without depending on external
> systems. e.g. updating the pattern by directly talking to the Flink job
> itself.
> - Some sort of isolation between patterns. e.g. a pattern update failure
> won't cause other running patterns to fail.
> - Easy to query the currently running patterns in the Flink job.
> - Extensible to add new features. e.g. apply some pattern to a subset of
> subtasks. Disable dynamic pattern update during a service window, etc.
>
> It looks to me that OC is a more promising way to to achieve the above.
>
> Please also see the reply to your questions inline below.
>
> > You mentioned that a TM might find out that a pattern is invalid and then
> > it could use the 2-way communication with the JM to tell the other TMs
> that
> > the pattern is invalid. How exactly would a TM detect that a pattern is
> > invalid at data processing time? And assuming that this is possible for a
> > single TM, why can't the other TMs not detect this problem? Is it because
> > the validity of patterns might depend on data that is different between
> > TMs?
>
>
> Yes, the TMs are processing different records, so some may encounter issue
> while others are running fine, for example, a field may be missing from a
> record while the pattern requires it. Even if all the TMs have detected the
> problem, without a channel to report back the issue, the only thing TMs can
> do is either to throw exception and stop processing.
>
> You also mentioned that deep-learning-on-flink could benefit from an OC
> > control plane but I couldn't find the referenced link. Would
> > deep-learning-on-flink like to use OCs as a kind of parameter server?
> Could
> > you elaborate on deep-learning-on-flink's usage of such a feature?
>
>
> deep-learning-on-flink[1] has a general ML cluster abstraction that can run
> TF / PyTorch etc. This cluster has a ML master role to manage the
> liveliness of all the ML workers which are python processes running
> side-by-side with TMs. The ML workers can be PS or Worker of TensorFlow.
> For example, if 10 TF worker and 5 TF PS nodes are needed, a Flink UDF
> operator of parallelism 10 and a Flink Source operator with parallelism = 5
> will be created to run the TF worker and TF PS respectively. All the 15
> nodes running either PS or Worker are managed by the ML master. Prior to
> OC, the implementation was having a Source operator with parallelism = 1 to
> run the master; let the ML workers register themselves to the an external
> ZK so the master can discover them. So basically users have to build their
> own control plane. With OC, at very least, we no longer need ZK anymore.
>
> Concerning reprocessing command history and repeatable processing results I
> > think there is actually quite a big difference between using a Flink
> source
> > vs. offering a REST server that can receive command that are distributed
> > via the OCs. In the former case we can rely on the external system to
> > persist commands whereas in the latter approach we/users have to
> implement
> > a storage solution on their own (in the simplest case users will probably
> > store everything in state which might grow indefinitely if stored as a
> > changelog).
>
>
> It is true that a Flink Source is easier to provide a change log of
> patterns. But there are also downsides. The most prominent one is that in
> order to update the dynamic pattern, users have to run an external system
> for the source to read. Or users have to implement a REST Source taking
> command directly like a web server. In that case, the service discovery is
> again a problem and needs external dependency.
> On the other hand, it is not so difficult for OC to store a change log
> history. Assuming there are 100 pattern updates / day for a CEP job and one
> year of history should be stored. Let's say each pattern change log entry
> is 1K bytes. The pattern update change log for the entire year is just 34
> MB, which seems quite small. And users can also query the patterns in
> effect via the same endpoint. I think this would provide a good out-of-box
> experience in the vast majority of cases. No external dependencies and a
> single REST endpoint. In rare cases where there is a large amount of
> pattern update log. External systems can still be leveraged. One potential
> issue might be that a command that has been received but not checkpointed
> yet may got lost if the job fails over. This can be mitigated by allowing
> OC to ask JM to trigger a checkpoint (not there yet but may worth
> thinking), or simply introduce a *PendingCommit* state for a pattern
> indicating it's not committed yet. In the worst case, we can always
> fallback to store patterns in external systems such as a database.
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
> [1]
>
> https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
>
>
> On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <tr...@apache.org> wrote:
>
> > Hi Becket,
> >
> > Thanks for the explanation. While I do agree that a general 2-way
> > communication pattern would be nice to have, I also believe that this
> > approach is probably at least one magnitude more complex to realize than
> > the side-input approach. Therefore, I really would like to understand why
> > such a mechanism is required for the CEP use case.
> >
> > You mentioned that a TM might find out that a pattern is invalid and then
> > it could use the 2-way communication with the JM to tell the other TMs
> that
> > the pattern is invalid. How exactly would a TM detect that a pattern is
> > invalid at data processing time? And assuming that this is possible for a
> > single TM, why can't the other TMs not detect this problem? Is it because
> > the validity of patterns might depend on data that is different between
> > TMs?
> >
> > You also mentioned that deep-learning-on-flink could benefit from an OC
> > control plane but I couldn't find the referenced link. Would
> > deep-learning-on-flink like to use OCs as a kind of parameter server?
> Could
> > you elaborate on deep-learning-on-flink's usage of such a feature?
> >
> > Concerning reprocessing command history and repeatable processing
> results I
> > think there is actually quite a big difference between using a Flink
> source
> > vs. offering a REST server that can receive command that are distributed
> > via the OCs. In the former case we can rely on the external system to
> > persist commands whereas in the latter approach we/users have to
> implement
> > a storage solution on their own (in the simplest case users will probably
> > store everything in state which might grow indefinitely if stored as a
> > changelog).
> >
> > Cheers,
> > Till
> >
> > On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com> wrote:
> >
> > > Hi David,
> > >
> > > Thanks for sharing your thoughts. Some quick reply to your comments:
> > >
> > > We're still talking about the "web server based"
> > > > pattern_processor_discoverer, but what about other use cases? One of
> my
> > > big
> > > > concerns is that user's can not really reuse any part of the Flink
> > > > ecosystem to implement the discovery logic. For example if they want
> to
> > > > read patterns from Kafka topic, they need to roll their own
> discoverer
> > > > based on the vanilla Kafka client. If we're talking about
> > extensibility,
> > > > should we also make sure that the existing primitives can be reused?
> > >
> > >
> > > KafkaSource is actually more complicated than vanilla KafkaConsumer
> from
> > > the perspective of consuming Kafka messages. The KafkaSource just helps
> > > make it easier for Flink jobs to process these messages. In fact,
> > > KafkaConsumer is more powerful than KafkaSource in terms of talking to
> > > Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator] and
> > > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> > >
> > > This can be done for the side-input as well by filtering invalid
> patterns
> > > > before the broadcast. You can also send the invalid patterns to any
> > side
> > > > output you want. I have a feeling that we're way too attached to the
> > REST
> > > > server use case in this discussion. I agree that for that case, this
> > > > solution is the most straightforward one.
> > >
> > >
> > > Depending on whether the invalidity is discovered in pattern definition
> > > time or data processing time. e.g. A valid pattern with invalid data
> > which
> > > fails to process can only be detected in data processing time. So the
> > > pattern won't be filtered out before the broadcast.
> > >
> > > I agree that 2-way communication in the "data-flow like" API is tricky,
> > > > because it requires cycles / iterations, which are still not really
> > > solved
> > > > (for a good reason, it's really tough nut to crack). This makes me
> > think
> > > > that the OC may be bit of a "incomplete" workaround for not having
> > fully
> > > > working support for iterations.
> > >
> > >
> > > For example I'm not really confident that the checkpointing of the OC
> > works
> > > > correctly right now, because it doesn't seem to require checkpoint
> > > barrier
> > > > alignment as the regular stream inputs. We also don't have a proper
> > > support
> > > > for watermarking (this is again tricky, because of the cycle).
> > >
> > >
> > > If we decide to go down this road, should we first address some of
> these
> > > > limitations?
> > >
> > > I agree. OC is proven to be useful and we should think about how to
> > enhance
> > > it instead of not using it.
> > >
> > > If I understand that correctly, this means only the LATEST state of the
> > > > patterns (in other words - patterns that are currently in use). Is
> this
> > > > really sufficient for historical re-processing? Can someone for
> example
> > > > want re-process the data in more of a "temporal join" fashion? Also
> > AFAIK
> > > > historical processing in combination with "coordinator checkpoints"
> is
> > > not
> > > > really something that we currently support of the box, are there any
> > > plans
> > > > on tackling this (my other concern is that this should not go against
> > the
> > > > "unified batch & stream processing" efforts)?
> > >
> > > I think in this case, the state would contain the entire pattern update
> > > history. Not the final state, but the change log. In fact, it is not
> > > possible to guarantee the correct result unless you have the entire
> > change
> > > log. Even with side-input, there still could be late arrivals in the
> > > pattern update stream, and the only way to correct it is to either have
> > all
> > > the data reprocessed (with all the pattern change log loaded upfront)
> or
> > > having retraction support.
> > >
> > > I can imagine that if this should be a concern, we could move the
> > execution
> > > > of the OC to the task managers. This also makes me thing, that we
> > > shouldn't
> > > > make any strong assumptions that the OC will always run in the
> > JobManager
> > > > (this is especially relevant for the embedded web-server use case).
> > >
> > > This is a very good point. I think we should do this. The reason OC is
> in
> > > JM is based on the assumption that control plane usually have little
> > > traffic. But if that is not the case, we should move the OC out of JM,
> > > maybe to TM.
> > >
> > >
> > >
> > > I think the key topic we are discussing is what the Flink control plane
> > > should look like, and CEP is just an example use case. There are
> > basically
> > > two options:
> > >
> > > 1. Using the side-input / broadcast stream
> > > 2. Using the OperatorCoordinator.
> > >
> > > Although we are having this discussion under the context of supporting
> > CEP
> > > dynamic pattern update, it would be really helpful to reach agreement
> on
> > > the design principle in general of how Flink should handle similar
> > external
> > > control demands, a.k.a how to provide a decent control plane in Flink
> to
> > > the users.
> > >
> > > Here is my take on these two options, based on the requirements of a
> > > control plane.
> > >
> > > *Communication Requirements*
> > > Flink has two kinds of control planes - in-band and out-of-band.
> > > In-band control plane is like watermark and checkpoint marker. It
> > requires
> > > the entire DAG to be in a consistent state, so the control messages
> flow
> > > with the data in one direction. This is a one-way control flow.
> > > Examples of out-of-band control plane is OC and JM/TM communication.
> They
> > > do not require a global consistency or awareness across the entire DAG.
> > >
> > > Before OC, neither of these two kinds of control plain was exposed to
> the
> > > users. OC allows the users to leverage the out-of-band control plane so
> > > they can coordinate across subtasks. This is a more widely used control
> > > flow from user defined operator perspective which requires 2-way
> > > communication.
> > >
> > > - side-input stream is one-way communication. Moreover, I don't
> think
> > > iteration is the right way to address this. Unlike the abstraction
> of
> > > data
> > > processing which is a DAG, the control plane may require
> communication
> > > between arbitrary two operators in different orders. Using
> iterations
> > > may
> > > end up with an explosion of feedback edges that are not only
> > > complicated to
> > > express, but also hard to debug and maintain.
> > > - OC provides a decent 2-way communication mechanism.
> > >
> > >
> > > *Cost for low traffic use case*
> > > An important difference between data channel and control channel is
> > traffic
> > > pattern. Unlike data plane, the control plane is usually idle for the
> > vast
> > > majority of the time with occasional control messages.
> > >
> > > - One argument to use the side-input / broadcast stream was that
> users
> > > can reuse the existing connectors. However, most Flink sources are
> > > designed
> > > to handle large throughput of traffic that maintains all the
> threads,
> > > network connections, etc. Not to say the external resources such as
> > > Kafka
> > > topics to store the commands.
> > > - OC can have a much lower constant cost.
> > >
> > >
> > > *Easy to use*
> > > Personally speaking, I think the most simple and user-friendly
> interface
> > is
> > > a REST API that accepts control commands.
> > >
> > > - One proposal at this point is to have a separate web server
> > > independent of the Flink job. In that case, should users implement
> > that
> > > web
> > > server? In order to pass the command to the Flink job, does that
> mean
> > > users
> > > should implement a Flink source that can read the commands from the
> > web
> > > server? Or the web server would send the command to something like
> > Kafka
> > > and let the Flink side-input read from there. There seems to be a
> lot
> > > for
> > > the users to do. And it seems an unnecessarily complicated system to
> > > build
> > > to send occasional control messages to a Flink job.
> > > - OC can simply be reached via the JM REST API.
> > > - e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx> would
> simply
> > > send the Content to the OC of OP_NAME.
> > >
> > > *Work well with checkpoints*
> > >
> > > - side-input streams works well with checkpoint, thanks to its
> > > compatibility to the DAG abstraction.
> > > - The OperatorCoordinator requires more careful design to work well
> > with
> > > checkpoints. The complexity mostly comes from the 2-way
> communication.
> > > At
> > > this point the OperatorCoordinator message delivery semantic may not
> > be
> > > as
> > > robust as side-input streams. However, I think this is mainly due to
> > > potential bugs in implementation instead of fundamental design
> > problems.
> > > Basically the checkpoint semantic should be:
> > > - The JM will first checkpoint all the OperatorCoordinator, more
> > > specifically for each OperatorCoordinator,
> > > - 1) JM blocks the input queue to stop receiving new events
> from
> > > the subtasks.
> > > - 2) let all the operator coordinator finish processing all
> the
> > > pending events in the OC input queue.
> > > - 3) flush the OC output queue until all the events sent are
> > > acknowledged.
> > > - 3) unblock the input queue, but block the output queue until
> > all
> > > the subtasks of the OC finish checkpoints.
> > > - The JM starts a normal checkpoint starting from the Source.
> > > - If an operator has a coordinator, and it has sent some
> events
> > to
> > > the OC but has not been acknowledged. These events need to be
> > > put into the
> > > subtasks' checkpoint.
> > > - After all the subtasks of an operator finishes checkpoint, the
> > > output queue of the corresponding OC can be unblocked.
> > > It looks that the above protocol would let OC have a clear
> checkpoint
> > > semantic. And this complexity seems must for 2-way communication. I
> > > think
> > > we are able to hide the above protocol from users by having an
> > abstract
> > > OC
> > > implementation.
> > >
> > >
> > > *Reprocess command history and repeatable processing results*
> > > This seems not something generally required for a control plane. But if
> > the
> > > control plane changes the data processing behavior, there might be some
> > use
> > > case. Just like the CEP pattern update. In order to do this, users will
> > > need to provide a full command history to the operators. That consists
> of
> > > two steps:
> > >
> > > 1. get the full command history. (Flink Source V.S. Custom way to
> > > retrieve command history.)
> > > 2. send them to the operators. (Side-input V.S. OC/Operator
> > > communication)l
> > >
> > > I actually don't feel much difference between these two options. I am
> not
> > > sure if a Flink source is necessarily simpler than the user implemented
> > > logic. For example, if all the changes are just written in a database
> > > table. From the user's perspective, I feel fine with querying the DB by
> > > myself using something like JDBC (or use KafkaConsumer to read the
> > pattern
> > > history from a Kafka topic) and send all the pattern change history to
> > the
> > > operators before they start to process the actual events.
> > >
> > > *Stability impact to the Flink Job*
> > > I agree this is a valid concern. There is only one JM and currently OC
> > runs
> > > there, which may potentially cause JM crash and result in job failure.
> > > Running in TM may have a less impact. So I think it makes sense to run
> OC
> > > in TM. However, this is more of how we can implement OC to make it more
> > > robust. It does not forfeit the other semantic and user experience
> > benefits
> > > mentioned above.
> > >
> > >
> > > To sum up:
> > > 1. Regardless of whether CEP chooses OC or side-input stream, a decent
> > > 2-way communication control plane seems really helpful and has been
> > proven
> > > by quite a few existing use cases. To me the question is how to make it
> > > more robust, not whether we should use it or not.
> > > 2. As for CEP, if we assume OC will be robust enough, personally I feel
> > OC
> > > is a better fit than side-input mainly because of the simplicity and
> > > extensibility.
> > >
> > > Thanks,
> > >
> > > Jiangjie (Becket) Qin
> > >
> > >
> > > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org> wrote:
> > >
> > > > Hi all,
> > > >
> > > > sorry for the late reply, vacation season ;) I'm still not 100% sold
> on
> > > > choosing the OC for this use-case, but on the other hand I don't have
> > > > strong arguments against it. Few more questions / thoughts:
> > > >
> > > > We're still talking about the "web server based"
> > > > pattern_processor_discoverer, but what about other use cases? One of
> my
> > > big
> > > > concerns is that user's can not really reuse any part of the Flink
> > > > ecosystem to implement the discovery logic. For example if they want
> to
> > > > read patterns from Kafka topic, they need to roll their own
> discoverer
> > > > based on the vanilla Kafka client. If we're talking about
> > extensibility,
> > > > should we also make sure that the existing primitives can be reused?
> > > >
> > > > For instance, the example I gave in my previous email seems not
> easily
> > > > > achievable with side-input / broadcast streams: a single invalid
> > > pattern
> > > > > detected on a TM can be disabled elegantly globally without
> crashing
> > > the
> > > > > entire Flink job.
> > > >
> > > >
> > > > This can be done for the side-input as well by filtering invalid
> > patterns
> > > > before the broadcast. You can also send the invalid patterns to any
> > side
> > > > output you want. I have a feeling that we're way too attached to the
> > REST
> > > > server use case in this discussion. I agree that for that case, this
> > > > solution is the most straightforward one.
> > > >
> > > > OC is a 2-way communication mechanism, i.e. a subtask can also send
> > > > > OperatorEvent to the coordinator to report its owns status, so that
> > the
> > > > > coordinator can act accordingly.
> > > > >
> > > >
> > > > I agree that 2-way communication in the "data-flow like" API is
> tricky,
> > > > because it requires cycles / iterations, which are still not really
> > > solved
> > > > (for a good reason, it's really tough nut to crack). This makes me
> > think
> > > > that the OC may be bit of a "incomplete" workaround for not having
> > fully
> > > > working support for iterations.
> > > >
> > > > For example I'm not really confident that the checkpointing of the OC
> > > works
> > > > correctly right now, because it doesn't seem to require checkpoint
> > > barrier
> > > > alignment as the regular stream inputs. We also don't have a proper
> > > support
> > > > for watermarking (this is again tricky, because of the cycle).
> > > >
> > > > If we decide to go down this road, should we first address some of
> > these
> > > > limitations?
> > > >
> > > > OperatorCoordinator will checkpoint the full amount of
> PatternProcessor
> > > > > data. For the reprocessing of historical data, you can read the
> > > > > PatternProcessor snapshots saved by this checkpoint from a certain
> > > > > historical checkpoint, and then recreate the historical data
> through
> > > > these
> > > > > PatternProcessor snapshots.
> > > > >
> > > >
> > > > If I understand that correctly, this means only the LATEST state of
> the
> > > > patterns (in other words - patterns that are currently in use). Is
> this
> > > > really sufficient for historical re-processing? Can someone for
> example
> > > > want re-process the data in more of a "temporal join" fashion? Also
> > AFAIK
> > > > historical processing in combination with "coordinator checkpoints"
> is
> > > not
> > > > really something that we currently support of the box, are there any
> > > plans
> > > > on tackling this (my other concern is that this should not go against
> > the
> > > > "unified batch & stream processing" efforts)?
> > > >
> > > > I do agree that having the user defined control logic defined in the
> JM
> > > > > increases the chance of instability.
> > > > >
> > > >
> > > > I can imagine that if this should be a concern, we could move the
> > > execution
> > > > of the OC to the task managers. This also makes me thing, that we
> > > shouldn't
> > > > make any strong assumptions that the OC will always run in the
> > JobManager
> > > > (this is especially relevant for the embedded web-server use case).
> > > >
> > > > If an agreement is reached on OperatorCoodinator, I will start the
> > voting
> > > > > thread.
> > > > >
> > > >
> > > > As for the vote, I'd would be great if we can wait until the next
> week
> > as
> > > > many people took vacation until end of the year.
> > > >
> > > > Overall, I really like the feature, this will be a great addition to
> > > Flink.
> > > >
> > > > Best,
> > > > D.
> > > >
> > > >
> > > >
> > > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <
> martijn@ververica.com
> > >
> > > > wrote:
> > > >
> > > > > Hi all,
> > > > >
> > > > > I can understand the need for a control plane mechanism. I'm not
> the
> > > > > technical go-to person for questions on the OperatorCoordinator,
> but
> > I
> > > > > would expect that we could offer those interfaces from Flink but
> > > > shouldn't
> > > > > recommend running user-code in the JobManager itself. I think the
> > user
> > > > code
> > > > > (like a webserver) should run outside of Flink (like via a sidecar)
> > and
> > > > use
> > > > > only the provided interfaces to communicate.
> > > > >
> > > > > I would like to get @David Morávek <dm...@apache.org> opinion on
> the
> > > > > technical part.
> > > > >
> > > > > Best regards,
> > > > >
> > > > > Martijn
> > > > >
> > > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> > nicholasjiang@apache.org
> > > >
> > > > > wrote:
> > > > >
> > > > >> Hi Konstantin, Becket, Martijn,
> > > > >>
> > > > >> Thanks for sharing your feedback. What other concerns do you have
> > > about
> > > > >> OperatorCoodinator? If an agreement is reached on
> > OperatorCoodinator,
> > > I
> > > > >> will start the voting thread.
> > > > >>
> > > > >> Best,
> > > > >> Nicholas Jiang
> > > > >>
> > > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > > >> > Hi Konstantin,
> > > > >> >
> > > > >> > Thanks for sharing your thoughts. Please see the reply inline
> > below.
> > > > >> >
> > > > >> > Thanks,
> > > > >> >
> > > > >> > Jiangjie (Becket) Qin
> > > > >> >
> > > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> > knaufk@apache.org
> > > >
> > > > >> wrote:
> > > > >> >
> > > > >> > > Hi Becket, Hi Nicholas,
> > > > >> > >
> > > > >> > > Thanks for joining the discussion.
> > > > >> > >
> > > > >> > > 1 ) Personally, I would argue that we should only run user
> code
> > in
> > > > the
> > > > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems wrong to
> > me
> > > to
> > > > >> > > encourage users to e.g. run a webserver on the Jobmanager, or
> > > > >> continuously
> > > > >> > > read patterns from a Kafka Topic on the Jobmanager, but both
> of
> > > > these
> > > > >> I see
> > > > >> > > happening with the current design. We've had lots of issues
> with
> > > > >> > > classloading leaks and other stability issues on the
> Jobmanager
> > > and
> > > > >> making
> > > > >> > > this more complicated, if there is another way, seems
> > unnecessary.
> > > > >> >
> > > > >> >
> > > > >> > I think the key question here is what primitive does Flink
> provide
> > > to
> > > > >> > facilitate the user implementation of their own control logic /
> > > > control
> > > > >> > plane? It looks that previously, Flink assumes that all the user
> > > logic
> > > > >> is
> > > > >> > just data processing logic without any control / coordination
> > > > >> requirements.
> > > > >> > However, it turns out that a decent control plane abstraction is
> > > > >> required
> > > > >> > in association with the data processing logic in many cases,
> > > including
> > > > >> > Source / Sink and other user defined operators in general. The
> > fact
> > > > >> that we
> > > > >> > ended up with adding the SplitEnumerator and GlobalCommitter are
> > > just
> > > > >> two
> > > > >> > examples of the demand of such coordination among user defined
> > > logics.
> > > > >> > There are other cases that we see in ecosystem projects, such as
> > > > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > > > >> >
> > > > >> > Such control plane primitives are critical to the extensibility
> > of a
> > > > >> > project. If we look at other projects, exposing such control
> plane
> > > > >> logic is
> > > > >> > quite common. For example, Hadoop ended up with exposing YARN
> as a
> > > > >> public
> > > > >> > API to the users, which is extremely popular. Kafka consumers
> > > exposed
> > > > >> the
> > > > >> > consumer group rebalance logic to the users via
> > > > >> ConsumerPartitionAssigner,
> > > > >> > which is also a control plane primitive.
> > > > >> >
> > > > >> > To me it is more important to think about how we can improve the
> > > > >> stability
> > > > >> > of such a control plane mechanism, instead of simply saying no
> to
> > > the
> > > > >> users.
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> > > 2) In addition, I suspect that, over time we will have to
> > > implement
> > > > >> all the
> > > > >> > > functionality that regular sources already provide around
> > > > consistency
> > > > >> > > (watermarks, checkpointing) for the
> PatternProcessorCoordinator,
> > > > too.
> > > > >> >
> > > > >> >
> > > > >> > I think OperatorCoordinator should have a generic communication
> > > > >> mechanism
> > > > >> > for all the operators, not specific to Source. We should
> probably
> > > have
> > > > >> an
> > > > >> > AbstractOperatorCoordinator help dealing with the communication
> > > layer,
> > > > >> and
> > > > >> > leave the state maintenance and event handling logic to the user
> > > code.
> > > > >> >
> > > > >> >
> > > > >> > > 3) I understand that running on the Jobmanager is easier if
> you
> > > want
> > > > >> to
> > > > >> > > launch a REST server directly. Here my question would be: does
> > > this
> > > > >> really
> > > > >> > > need to be solved inside of Flink or couldn't you start a
> > > webserver
> > > > >> next to
> > > > >> > > Flink? If we start using the Jobmanager as a REST server users
> > > will
> > > > >> expect
> > > > >> > > that e.g. it is highly available and can be load balanced and
> we
> > > > >> quickly
> > > > >> > > need to think about aspects that we never wanted to think
> about
> > in
> > > > the
> > > > >> > > context of a Flink Jobmanager.
> > > > >> > >
> > > > >> >
> > > > >> > I think the REST API is just for receiving commands targeting a
> > > > running
> > > > >> > Flink job. If the job fails, the REST API would be useless.
> > > > >> >
> > > > >> >
> > > > >> > > So, can you elaborate a bit more, why a side-input/broadcast
> > > stream
> > > > is
> > > > >> > >
> > > > >> > > a) more difficult
> > > > >> > > b) has vague semantics (To me semantics of a stream-stream
> seem
> > > > >> clearer
> > > > >> > > when it comes to out-of-orderness, late data, reprocessing or
> > > batch
> > > > >> > > execution mode.)
> > > > >> >
> > > > >> >
> > > > >> > I do agree that having the user defined control logic defined in
> > the
> > > > JM
> > > > >> > increases the chance of instability. In that case, we may think
> of
> > > > other
> > > > >> > solutions and I am fully open to that. But the side-input /
> > > broadcast
> > > > >> > stream seems more like a bandaid instead of a carefully designed
> > > > control
> > > > >> > plane mechanism.
> > > > >> >
> > > > >> > A decent control plane requires two-way communication, so
> > > information
> > > > >> can
> > > > >> > be reported / collected from the entity being controlled, and
> the
> > > > >> > coordinator / controller can send decisions or commands to the
> > > > entities
> > > > >> > accordingly, just like our TM / JM communication. IIUC, this is
> > not
> > > > >> > achievable with the existing side-input / broadcast stream as
> both
> > > of
> > > > >> them
> > > > >> > are one-way communication mechanisms. For instance, the example
> I
> > > gave
> > > > >> in
> > > > >> > my previous email seems not easily achievable with side-input /
> > > > >> broadcast
> > > > >> > streams: a single invalid pattern detected on a TM can be
> disabled
> > > > >> > elegantly globally without crashing the entire Flink job.
> > > > >> >
> > > > >> >
> > > > >> > > Cheers,
> > > > >> > >
> > > > >> > > Konstantin
> > > > >> > >
> > > > >> > >
> > > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> > becket.qin@gmail.com
> > > >
> > > > >> wrote:
> > > > >> > >
> > > > >> > > > Hi folks,
> > > > >> > > >
> > > > >> > > > I just finished reading the previous emails. It was a good
> > > > >> discussion.
> > > > >> > > Here
> > > > >> > > > are my two cents:
> > > > >> > > >
> > > > >> > > > *Is OperatorCoordinator a public API?*
> > > > >> > > > Regarding the OperatorCoordinator, although it is marked as
> > > > internal
> > > > >> > > > interface at this point, I intended to make it a public
> > > interface
> > > > >> when
> > > > >> > > add
> > > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> > communication
> > > > >> mechanism
> > > > >> > > > that enables many use cases, Source / Sink / TF on Flink /
> CEP
> > > > here
> > > > >> > > again.
> > > > >> > > > To my understanding, OC was marked as internal because we
> > think
> > > it
> > > > >> is not
> > > > >> > > > stable enough yet. We may need to fortify the OperatorEvent
> > > > delivery
> > > > >> > > > semantic a little bit so it works well with checkpoint in
> > > general.
> > > > >> > > >
> > > > >> > > > I think it is a valid concern that user code running in JM
> may
> > > > cause
> > > > >> > > > instability. However, not providing this communication
> > mechanism
> > > > >> only
> > > > >> > > makes
> > > > >> > > > a lot of use case even harder to implement. So it seems that
> > > > having
> > > > >> the
> > > > >> > > OC
> > > > >> > > > exposed to end users brings more benefits than harm to
> Flink.
> > At
> > > > >> the end
> > > > >> > > of
> > > > >> > > > the day, users have many ways to crash a Flink job if they
> do
> > > not
> > > > >> write
> > > > >> > > > proper code. So making those who know what they do happy
> seems
> > > > more
> > > > >> > > > important here.
> > > > >> > > >
> > > > >> > > > *OperatorCoordinator V.S. side-input / broadcast stream*
> > > > >> > > > I think both of them can achieve the goal of dynamic
> patterns.
> > > The
> > > > >> main
> > > > >> > > > difference is the extensibility.
> > > > >> > > >
> > > > >> > > > OC is a 2-way communication mechanism, i.e. a subtask can
> also
> > > > send
> > > > >> > > > OperatorEvent to the coordinator to report its owns status,
> so
> > > > that
> > > > >> the
> > > > >> > > > coordinator can act accordingly. This is sometimes useful.
> For
> > > > >> example, a
> > > > >> > > > single invalid pattern can be disabled elegantly without
> > > crashing
> > > > >> the
> > > > >> > > > entire Flink job. In the future, if we allow users to send
> > > > external
> > > > >> > > command
> > > > >> > > > to OC via JM, a default self-contained implementation can
> just
> > > > >> update the
> > > > >> > > > pattern via the REST API without external dependencies.
> > > > >> > > >
> > > > >> > > > Another reason I personally prefer OC is because it is an
> > > explicit
> > > > >> > > control
> > > > >> > > > plain mechanism, where as the side-input / broadcast stream
> > has
> > > > are
> > > > >> more
> > > > >> > > > vague semantic.
> > > > >> > > >
> > > > >> > > > Thanks,
> > > > >> > > >
> > > > >> > > > Jiangjie (Becket) Qin
> > > > >> > > >
> > > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> > dmvk@apache.org>
> > > > >> wrote:
> > > > >> > > >
> > > > >> > > > > Hi Yunfeng,
> > > > >> > > > >
> > > > >> > > > > thanks for drafting this FLIP, this will be a great
> addition
> > > > into
> > > > >> the
> > > > >> > > CEP
> > > > >> > > > > toolbox!
> > > > >> > > > >
> > > > >> > > > > Apart from running user code in JM, which want to avoid in
> > > > >> general, I'd
> > > > >> > > > > have one more another concern about using the
> > > > OperatorCoordinator
> > > > >> and
> > > > >> > > > that
> > > > >> > > > > is re-processing of the historical data. Any thoughts
> about
> > > how
> > > > >> this
> > > > >> > > will
> > > > >> > > > > work with the OC?
> > > > >> > > > >
> > > > >> > > > > I have a slight feeling that a side-input (custom source /
> > > > >> operator +
> > > > >> > > > > broadcast) would a better fit for this case. This would
> > > simplify
> > > > >> the
> > > > >> > > > > consistency concerns (watermarks + pushback) and the
> > > > >> re-processing of
> > > > >> > > > > historical data.
> > > > >> > > > >
> > > > >> > > > > Best,
> > > > >> > > > > D.
> > > > >> > > > >
> > > > >> > > > >
> > > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > > >> > > nicholasjiang@apache.org
> > > > >> > > > >
> > > > >> > > > > wrote:
> > > > >> > > > >
> > > > >> > > > > > Hi Konstantin, Martijn
> > > > >> > > > > >
> > > > >> > > > > > Thanks for the detailed feedback in the discussion.
> What I
> > > > >> still have
> > > > >> > > > > left
> > > > >> > > > > > to answer/reply to:
> > > > >> > > > > >
> > > > >> > > > > > -- Martijn: Just to be sure, this indeed would mean that
> > if
> > > > for
> > > > >> > > > whatever
> > > > >> > > > > > reason the heartbeat timeout, it would crash the job,
> > right?
> > > > >> > > > > >
> > > > >> > > > > > IMO, if for whatever reason the heartbeat timeout, it
> > > couldn't
> > > > >> check
> > > > >> > > > the
> > > > >> > > > > > PatternProcessor consistency between the
> > OperatorCoordinator
> > > > >> and the
> > > > >> > > > > > subtasks so that the job would be crashed.
> > > > >> > > > > >
> > > > >> > > > > > -- Konstantin: What I was concerned about is that we
> > > basically
> > > > >> let
> > > > >> > > > users
> > > > >> > > > > > run a UserFunction in the OperatorCoordinator, which it
> > does
> > > > >> not seem
> > > > >> > > > to
> > > > >> > > > > > have been designed for.
> > > > >> > > > > >
> > > > >> > > > > > In general, we have reached an agreement on the design
> of
> > > this
> > > > >> FLIP,
> > > > >> > > > but
> > > > >> > > > > > there are some concerns on the OperatorCoordinator,
> about
> > > > >> whether
> > > > >> > > > > basically
> > > > >> > > > > > let users run a UserFunction in the OperatorCoordinator
> is
> > > > >> designed
> > > > >> > > for
> > > > >> > > > > > OperatorCoordinator. We would like to invite Becket Qin
> > who
> > > is
> > > > >> the
> > > > >> > > > author
> > > > >> > > > > > of OperatorCoordinator to help us to answer this
> concern.
> > > > >> > > > > >
> > > > >> > > > > > Best,
> > > > >> > > > > > Nicholas Jiang
> > > > >> > > > > >
> > > > >> > > > > >
> > > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > > >> > > > > > > Hi all,
> > > > >> > > > > > >
> > > > >> > > > > > > Really like the discussion on this topic moving
> > forward. I
> > > > >> really
> > > > >> > > > think
> > > > >> > > > > > > this feature will be much appreciated by the Flink
> > users.
> > > > >> What I
> > > > >> > > > still
> > > > >> > > > > > have
> > > > >> > > > > > > left to answer/reply to:
> > > > >> > > > > > >
> > > > >> > > > > > > -- Good point. If for whatever reason the different
> > > > >> taskmanagers
> > > > >> > > > can't
> > > > >> > > > > > get
> > > > >> > > > > > > the latest rule, the Operator Coordinator could send a
> > > > >> heartbeat to
> > > > >> > > > all
> > > > >> > > > > > > taskmanagers with the latest rules and check the
> > heartbeat
> > > > >> response
> > > > >> > > > > from
> > > > >> > > > > > > all the taskmanagers whether the latest rules of the
> > > > >> taskmanager is
> > > > >> > > > > equal
> > > > >> > > > > > > to these of the Operator Coordinator.
> > > > >> > > > > > >
> > > > >> > > > > > > Just to be sure, this indeed would mean that if for
> > > whatever
> > > > >> reason
> > > > >> > > > the
> > > > >> > > > > > > heartbeat timeout, it would crash the job, right?
> > > > >> > > > > > >
> > > > >> > > > > > > -- We have consided about the solution mentioned
> above.
> > In
> > > > >> this
> > > > >> > > > > > solution, I
> > > > >> > > > > > > have some questions about how to guarantee the
> > consistency
> > > > of
> > > > >> the
> > > > >> > > > rule
> > > > >> > > > > > > between each TaskManager. By having a coodinator in
> the
> > > > >> JobManager
> > > > >> > > to
> > > > >> > > > > > > centrally manage the latest rules, the latest rules of
> > all
> > > > >> > > > TaskManagers
> > > > >> > > > > > are
> > > > >> > > > > > > consistent with those of the JobManager, so as to
> avoid
> > > the
> > > > >> > > > > > inconsistencies
> > > > >> > > > > > > that may be encountered in the above solution. Can you
> > > > >> introduce
> > > > >> > > how
> > > > >> > > > > this
> > > > >> > > > > > > solution guarantees the consistency of the rules?
> > > > >> > > > > > >
> > > > >> > > > > > > The consistency that we could guarantee was based on
> how
> > > > >> often each
> > > > >> > > > > > > TaskManager would do a refresh and how often we would
> > > > accept a
> > > > >> > > > refresh
> > > > >> > > > > to
> > > > >> > > > > > > fail. We set the refresh time to a relatively short
> one
> > > (30
> > > > >> > > seconds)
> > > > >> > > > > and
> > > > >> > > > > > > maximum failures to 3. That meant that we could
> > guarantee
> > > > that
> > > > >> > > rules
> > > > >> > > > > > would
> > > > >> > > > > > > be updated in < 2 minutes or else the job would crash.
> > > That
> > > > >> was
> > > > >> > > > > > sufficient
> > > > >> > > > > > > for our use cases. This also really depends on how big
> > > your
> > > > >> cluster
> > > > >> > > > > is. I
> > > > >> > > > > > > can imagine that if you have a large scale cluster
> that
> > > you
> > > > >> want to
> > > > >> > > > > run,
> > > > >> > > > > > > you don't want to DDOS the backend system where you
> have
> > > > your
> > > > >> rules
> > > > >> > > > > > stored.
> > > > >> > > > > > >
> > > > >> > > > > > > -- In summary, the current design is that JobManager
> > tells
> > > > all
> > > > >> > > > > > TaskManagers
> > > > >> > > > > > > the latest rules through OperatorCoodinator, and will
> > > > >> initiate a
> > > > >> > > > > > heartbeat
> > > > >> > > > > > > to check whether the latest rules on each TaskManager
> > are
> > > > >> > > consistent.
> > > > >> > > > > We
> > > > >> > > > > > > will describe how to deal with the Failover scenario
> in
> > > more
> > > > >> detail
> > > > >> > > > on
> > > > >> > > > > > FLIP.
> > > > >> > > > > > >
> > > > >> > > > > > > Thanks for that. I think having the JobManager tell
> the
> > > > >> > > TaskManagers
> > > > >> > > > > the
> > > > >> > > > > > > applicable rules would indeed end up being the best
> > > design.
> > > > >> > > > > > >
> > > > >> > > > > > > -- about the concerns around consistency raised by
> > > Martijn:
> > > > I
> > > > >> > > think a
> > > > >> > > > > lot
> > > > >> > > > > > > of those can be mitigated by using an event time
> > timestamp
> > > > >> from
> > > > >> > > which
> > > > >> > > > > the
> > > > >> > > > > > > rules take effect. The reprocessing scenario, for
> > example,
> > > > is
> > > > >> > > covered
> > > > >> > > > > by
> > > > >> > > > > > > this. If a pattern processor should become active as
> > soon
> > > as
> > > > >> > > > possible,
> > > > >> > > > > > > there will still be inconsistencies between
> > Taskmanagers,
> > > > but
> > > > >> "as
> > > > >> > > > soon
> > > > >> > > > > as
> > > > >> > > > > > > possible" is vague anyway, which is why I think that's
> > ok.
> > > > >> > > > > > >
> > > > >> > > > > > > I think an event timestamp is indeed a really
> important
> > > one.
> > > > >> We
> > > > >> > > also
> > > > >> > > > > used
> > > > >> > > > > > > that in my previous role, with the
> > ruleActivationTimestamp
> > > > >> compared
> > > > >> > > > to
> > > > >> > > > > > > eventtime (well, actually we used Kafka logAppend time
> > > > because
> > > > >> > > > > > > eventtime wasn't always properly set so we used that
> > time
> > > to
> > > > >> > > > overwrite
> > > > >> > > > > > the
> > > > >> > > > > > > eventtime from the event itself).
> > > > >> > > > > > >
> > > > >> > > > > > > Best regards,
> > > > >> > > > > > >
> > > > >> > > > > > > Martijn
> > > > >> > > > > > >
> > > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> > > > >> knaufk@apache.org>
> > > > >> > > > > > wrote:
> > > > >> > > > > > >
> > > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > > >> > > > > > > >
> > > > >> > > > > > > > about the concerns around consistency raised by
> > > Martijn: I
> > > > >> think
> > > > >> > > a
> > > > >> > > > > lot
> > > > >> > > > > > of
> > > > >> > > > > > > > those can be mitigated by using an event time
> > timestamp
> > > > from
> > > > >> > > which
> > > > >> > > > > the
> > > > >> > > > > > > > rules take effect. The reprocessing scenario, for
> > > example,
> > > > >> is
> > > > >> > > > covered
> > > > >> > > > > > by
> > > > >> > > > > > > > this. If a pattern processor should become active as
> > > soon
> > > > as
> > > > >> > > > > possible,
> > > > >> > > > > > > > there will still be inconsistencies between
> > > Taskmanagers,
> > > > >> but "as
> > > > >> > > > > soon
> > > > >> > > > > > as
> > > > >> > > > > > > > possible" is vague anyway, which is why I think
> that's
> > > ok.
> > > > >> > > > > > > >
> > > > >> > > > > > > > about naming: The naming with "PatternProcessor"
> > sounds
> > > > >> good to
> > > > >> > > me.
> > > > >> > > > > > Final
> > > > >> > > > > > > > nit: I would go for CEP#patternProccessors, which
> > would
> > > be
> > > > >> > > > consistent
> > > > >> > > > > > with
> > > > >> > > > > > > > CEP#pattern.
> > > > >> > > > > > > >
> > > > >> > > > > > > > I am not sure about one of the rejected
> alternatives:
> > > > >> > > > > > > >
> > > > >> > > > > > > > > Have each subtask of an operator make the update
> on
> > > > their
> > > > >> own
> > > > >> > > > > > > >
> > > > >> > > > > > > > -
> > > > >> > > > > > > >
> > > > >> > > > > > > > It is hard to achieve consistency.
> > > > >> > > > > > > > -
> > > > >> > > > > > > >
> > > > >> > > > > > > > Though the time interval that each subtask
> makes
> > > the
> > > > >> update
> > > > >> > > > can
> > > > >> > > > > > be
> > > > >> > > > > > > > the same, the absolute time they make the
> update
> > > > >> might be
> > > > >> > > > > > different.
> > > > >> > > > > > > > For
> > > > >> > > > > > > > example, one makes updates at 10:00, 10:05,
> etc,
> > > > while
> > > > >> > > > another
> > > > >> > > > > > does
> > > > >> > > > > > > > it at
> > > > >> > > > > > > > 10:01, 10:06. In this case the subtasks might
> > > never
> > > > >> > > > processing
> > > > >> > > > > > data
> > > > >> > > > > > > > with
> > > > >> > > > > > > > the same set of pattern processors.
> > > > >> > > > > > > >
> > > > >> > > > > > > >
> > > > >> > > > > > > > I would have thought that it is quite easy to poll
> for
> > > the
> > > > >> rules
> > > > >> > > > from
> > > > >> > > > > > each
> > > > >> > > > > > > > Subtask at *about *the same time. So, this alone
> does
> > > not
> > > > >> seem to
> > > > >> > > > be
> > > > >> > > > > > > > enough to rule out this option. I've looped in David
> > > > >> Moravek to
> > > > >> > > get
> > > > >> > > > > his
> > > > >> > > > > > > > opinion of the additional load imposed on the JM.
> > > > >> > > > > > > >
> > > > >> > > > > > > > Thanks,
> > > > >> > > > > > > >
> > > > >> > > > > > > > Konstantin
> > > > >> > > > > > > >
> > > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas Jiang <
> > > > >> > > > > > nicholasjiang@apache.org>
> > > > >> > > > > > > > wrote:
> > > > >> > > > > > > >
> > > > >> > > > > > > > > Hi Yue,
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > Thanks for your feedback of the FLIP. I have
> > addressed
> > > > >> your
> > > > >> > > > > > questions and
> > > > >> > > > > > > > > made a corresponding explanation as follows:
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > > >> > > PatternProcessoerDiscoverer
> > > > >> > > > to
> > > > >> > > > > > > > update
> > > > >> > > > > > > > > the rules, will it increase the load of JM? For
> > > example,
> > > > >> if the
> > > > >> > > > > user
> > > > >> > > > > > > > wants
> > > > >> > > > > > > > > the updated rule to take effect immediately,,
> which
> > > > means
> > > > >> that
> > > > >> > > we
> > > > >> > > > > > need to
> > > > >> > > > > > > > > set a shorter check interval or there is another
> > > > scenario
> > > > >> when
> > > > >> > > > > users
> > > > >> > > > > > > > rarely
> > > > >> > > > > > > > > update the pattern, will the
> > > PatternProcessoerDiscoverer
> > > > >> be in
> > > > >> > > > most
> > > > >> > > > > > of
> > > > >> > > > > > > > the
> > > > >> > > > > > > > > time Do useless checks ? Will a lazy update mode
> > could
> > > > be
> > > > >> used,
> > > > >> > > > > > which the
> > > > >> > > > > > > > > pattern only be updated when triggered by the
> user,
> > > and
> > > > do
> > > > >> > > > nothing
> > > > >> > > > > at
> > > > >> > > > > > > > other
> > > > >> > > > > > > > > times?
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > PatternProcessoerDiscoverer is a user-defined
> > > interface
> > > > to
> > > > >> > > > discover
> > > > >> > > > > > the
> > > > >> > > > > > > > > PatternProcessor updates. Periodically checking
> the
> > > > >> > > > > PatternProcessor
> > > > >> > > > > > in
> > > > >> > > > > > > > the
> > > > >> > > > > > > > > database is a implementation of the
> > > > >> PatternProcessoerDiscoverer
> > > > >> > > > > > > > interface,
> > > > >> > > > > > > > > which is that periodically querys all the
> > > > PatternProcessor
> > > > >> > > table
> > > > >> > > > in
> > > > >> > > > > > > > certain
> > > > >> > > > > > > > > interval. This implementation indeeds has the
> > useless
> > > > >> checks,
> > > > >> > > and
> > > > >> > > > > > could
> > > > >> > > > > > > > > directly integrates the changelog of the table. In
> > > > >> addition, in
> > > > >> > > > > > addition
> > > > >> > > > > > > > to
> > > > >> > > > > > > > > the implementation of periodically checking the
> > > > database,
> > > > >> there
> > > > >> > > > are
> > > > >> > > > > > other
> > > > >> > > > > > > > > implementations such as the PatternProcessor that
> > > > provides
> > > > >> > > > Restful
> > > > >> > > > > > > > services
> > > > >> > > > > > > > > to receive updates.
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > -- I still have some confusion about how Key
> > > Generating
> > > > >> > > > Opertator
> > > > >> > > > > > and
> > > > >> > > > > > > > > CepOperator (Pattern Matching & Processing
> Operator)
> > > > work
> > > > >> > > > together.
> > > > >> > > > > > If
> > > > >> > > > > > > > > there are N PatternProcessors, will the Key
> > Generating
> > > > >> > > Opertator
> > > > >> > > > > > > > generate N
> > > > >> > > > > > > > > keyedStreams, and then N CepOperator would process
> > > each
> > > > >> Key
> > > > >> > > > > > separately ?
> > > > >> > > > > > > > Or
> > > > >> > > > > > > > > every CepOperator Task would process all patterns,
> > if
> > > > so,
> > > > >> does
> > > > >> > > > the
> > > > >> > > > > > key
> > > > >> > > > > > > > type
> > > > >> > > > > > > > > in each PatternProcessor need to be the same?
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > Firstly the Pattern Matching & Processing Operator
> > is
> > > > not
> > > > >> the
> > > > >> > > > > > CepOperator
> > > > >> > > > > > > > > at present, because CepOperator mechanism is based
> > on
> > > > the
> > > > >> > > > NFAState.
> > > > >> > > > > > > > > Secondly if there are N PatternProcessors, the Key
> > > > >> Generating
> > > > >> > > > > > Opertator
> > > > >> > > > > > > > > combines all the keyedStreams with keyBy()
> > operation,
> > > > >> thus the
> > > > >> > > > > > Pattern
> > > > >> > > > > > > > > Matching & Processing Operator would process all
> the
> > > > >> patterns.
> > > > >> > > In
> > > > >> > > > > > other
> > > > >> > > > > > > > > words, the KeySelector of the PatternProcessor is
> > used
> > > > >> for the
> > > > >> > > > Key
> > > > >> > > > > > > > > Generating Opertator, and the Pattern and
> > > > >> > > PatternProceessFunction
> > > > >> > > > > of
> > > > >> > > > > > the
> > > > >> > > > > > > > > PatternProcessor are used for the Pattern
> Matching &
> > > > >> Processing
> > > > >> > > > > > Operator.
> > > > >> > > > > > > > > Lastly the key type in each PatternProcessor is
> the
> > > > same,
> > > > >> > > > regarded
> > > > >> > > > > as
> > > > >> > > > > > > > > Object type.
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > -- Maybe need to pay attention to it when
> > implementing
> > > > it
> > > > >> .If
> > > > >> > > > some
> > > > >> > > > > > > > Pattern
> > > > >> > > > > > > > > has been removed or updated, will the partially
> > > matched
> > > > >> results
> > > > >> > > > in
> > > > >> > > > > > > > > StateBackend would be clean up or We rely on state
> > ttl
> > > > to
> > > > >> clean
> > > > >> > > > up
> > > > >> > > > > > these
> > > > >> > > > > > > > > expired states.
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > If certain Pattern has been removed or updated,
> the
> > > > >> partially
> > > > >> > > > > matched
> > > > >> > > > > > > > > results in StateBackend would be clean up until
> the
> > > next
> > > > >> > > > > checkpoint.
> > > > >> > > > > > The
> > > > >> > > > > > > > > partially matched result doesn't depend on the
> state
> > > ttl
> > > > >> of the
> > > > >> > > > > > > > > StateBackend.
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > 4. Will the PatternProcessorManager keep all the
> > > active
> > > > >> > > > > > PatternProcessor
> > > > >> > > > > > > > > in memory? We have also Support Multiple Rule and
> > > > Dynamic
> > > > >> Rule
> > > > >> > > > > > Changing.
> > > > >> > > > > > > > > But we are facing such a problem, some users’
> usage
> > > > >> scenarios
> > > > >> > > are
> > > > >> > > > > > that
> > > > >> > > > > > > > they
> > > > >> > > > > > > > > want to have their own pattern for each user_id,
> > which
> > > > >> means
> > > > >> > > that
> > > > >> > > > > > there
> > > > >> > > > > > > > > could be thousands of patterns, which would make
> the
> > > > >> > > performance
> > > > >> > > > of
> > > > >> > > > > > > > Pattern
> > > > >> > > > > > > > > Matching very poor. We are also trying to solve
> this
> > > > >> problem.
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > The PatternProcessorManager keeps all the active
> > > > >> > > PatternProcessor
> > > > >> > > > > in
> > > > >> > > > > > > > > memory. For scenarios that they want to have their
> > own
> > > > >> pattern
> > > > >> > > > for
> > > > >> > > > > > each
> > > > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> > > fine-grained
> > > > >> pattern
> > > > >> > > > of
> > > > >> > > > > > > > > PatternProcessor to solve the performance problem
> of
> > > the
> > > > >> > > Pattern
> > > > >> > > > > > > > Matching,
> > > > >> > > > > > > > > for example, a pattern corresponds to a group of
> > > users?
> > > > >> The
> > > > >> > > > > scenarios
> > > > >> > > > > > > > > mentioned above need to be solved by case by case.
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > Best,
> > > > >> > > > > > > > > Nicholas Jiang
> > > > >> > > > > > > > >
> > > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > > >> > > > > > > > > > Glad to see the Community's progress in Flink
> CEP.
> > > > After
> > > > >> > > > reading
> > > > >> > > > > > this
> > > > >> > > > > > > > > Flip,
> > > > >> > > > > > > > > > I have few questions, would you please take a
> look
> > > ?
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > > >> > > > PatternProcessoerDiscoverer
> > > > >> > > > > to
> > > > >> > > > > > > > > update
> > > > >> > > > > > > > > > the rules, will it increase the load of JM? For
> > > > >> example, if
> > > > >> > > the
> > > > >> > > > > > user
> > > > >> > > > > > > > > wants
> > > > >> > > > > > > > > > the updated rule to take effect immediately,,
> > which
> > > > >> means
> > > > >> > > that
> > > > >> > > > we
> > > > >> > > > > > need
> > > > >> > > > > > > > to
> > > > >> > > > > > > > > > set a shorter check interval or there is
> another
> > > > >> scenario
> > > > >> > > when
> > > > >> > > > > > users
> > > > >> > > > > > > > > > rarely update the pattern, will the
> > > > >> > > PatternProcessoerDiscoverer
> > > > >> > > > > be
> > > > >> > > > > > in
> > > > >> > > > > > > > > most
> > > > >> > > > > > > > > > of the time Do useless checks ? Will a lazy
> update
> > > > mode
> > > > >> could
> > > > >> > > > be
> > > > >> > > > > > used,
> > > > >> > > > > > > > > > which the pattern only be updated when triggered
> > by
> > > > the
> > > > >> user,
> > > > >> > > > and
> > > > >> > > > > > do
> > > > >> > > > > > > > > > nothing at other times ?
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > > > 2. I still have some confusion about how Key
> > > > >> Generating
> > > > >> > > > > > Opertator and
> > > > >> > > > > > > > > > CepOperator (Pattern Matching & Processing
> > Operator)
> > > > >> work
> > > > >> > > > > > together. If
> > > > >> > > > > > > > > > there are N PatternProcessors, will the Key
> > > Generating
> > > > >> > > > Opertator
> > > > >> > > > > > > > > generate N
> > > > >> > > > > > > > > > keyedStreams, and then N CepOperator would
> process
> > > > each
> > > > >> Key
> > > > >> > > > > > separately
> > > > >> > > > > > > > ?
> > > > >> > > > > > > > > Or
> > > > >> > > > > > > > > > every CepOperator Task would process all
> patterns,
> > > if
> > > > >> so,
> > > > >> > > does
> > > > >> > > > > the
> > > > >> > > > > > key
> > > > >> > > > > > > > > type
> > > > >> > > > > > > > > > in each PatternProcessor need to be the same ?
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > > > 3. Maybe need to pay attention to it when
> > > implementing
> > > > >> it .If
> > > > >> > > > > some
> > > > >> > > > > > > > > Pattern
> > > > >> > > > > > > > > > has been removed or updateed ,will the
> partially
> > > > >> matched
> > > > >> > > > results
> > > > >> > > > > > in
> > > > >> > > > > > > > > > StateBackend would be clean up or We rely on
> state
> > > ttl
> > > > >> to
> > > > >> > > clean
> > > > >> > > > > up
> > > > >> > > > > > > > these
> > > > >> > > > > > > > > > expired states.
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > > > 4. Will the PatternProcessorManager keep all the
> > > > active
> > > > >> > > > > > > > PatternProcessor
> > > > >> > > > > > > > > in
> > > > >> > > > > > > > > > memory ? We have also Support Multiple Rule and
> > > > Dynamic
> > > > >> Rule
> > > > >> > > > > > Changing .
> > > > >> > > > > > > > > > But we are facing such a problem, some users’
> > usage
> > > > >> scenarios
> > > > >> > > > are
> > > > >> > > > > > that
> > > > >> > > > > > > > > they
> > > > >> > > > > > > > > > want to have their own pattern for each user_id,
> > > which
> > > > >> means
> > > > >> > > > that
> > > > >> > > > > > there
> > > > >> > > > > > > > > > could be thousands of patterns, which would make
> > the
> > > > >> > > > performance
> > > > >> > > > > of
> > > > >> > > > > > > > > Pattern
> > > > >> > > > > > > > > > Matching very poor. We are also trying to solve
> > this
> > > > >> problem.
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > > > Yunfeng Zhou <fl...@gmail.com>
> > > > >> 于2021年12月10日周五
> > > > >> > > > > 19:16写道：
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > > > > Hi all，
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > > > I'm opening this thread to propose the design
> to
> > > > >> support
> > > > >> > > > > multiple
> > > > >> > > > > > > > rule
> > > > >> > > > > > > > > &
> > > > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP
> project,
> > as
> > > > >> > > described
> > > > >> > > > in
> > > > >> > > > > > > > > FLIP-200
> > > > >> > > > > > > > > > > [1]
> > > > >> > > > > > > > > > > .
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > > > Currently Flink CEP only supports having a
> > single
> > > > >> pattern
> > > > >> > > > > inside
> > > > >> > > > > > a
> > > > >> > > > > > > > > > > CepOperator and does not support changing the
> > > > pattern
> > > > >> > > > > > dynamically. In
> > > > >> > > > > > > > > order
> > > > >> > > > > > > > > > > to reduce resource consumption and to
> experience
> > > > >> shorter
> > > > >> > > > > downtime
> > > > >> > > > > > > > > during
> > > > >> > > > > > > > > > > pattern updates, there is a growing need in
> the
> > > > >> production
> > > > >> > > > > > > > environment
> > > > >> > > > > > > > > that
> > > > >> > > > > > > > > > > expects CEP to support having multiple
> patterns
> > in
> > > > one
> > > > >> > > > operator
> > > > >> > > > > > and
> > > > >> > > > > > > > to
> > > > >> > > > > > > > > > > support dynamically changing them. Therefore I
> > > > >> propose to
> > > > >> > > add
> > > > >> > > > > > certain
> > > > >> > > > > > > > > > > infrastructure as described in FLIP-200 to
> > support
> > > > >> these
> > > > >> > > > > > > > > functionalities.
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > > > Please feel free to reply to this email
> thread.
> > > > >> Looking
> > > > >> > > > forward
> > > > >> > > > > > to
> > > > >> > > > > > > > your
> > > > >> > > > > > > > > > > feedback!
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > > > [1]
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > >
> > > > >> > > > > > > >
> > > > >> > > > > >
> > > > >> > > > >
> > > > >> > > >
> > > > >> > >
> > > > >>
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > > > Best regards,
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > > > Yunfeng
> > > > >> > > > > > > > > > >
> > > > >> > > > > > > > > >
> > > > >> > > > > > > > >
> > > > >> > > > > > > >
> > > > >> > > > > > > >
> > > > >> > > > > > > > --
> > > > >> > > > > > > >
> > > > >> > > > > > > > Konstantin Knauf
> > > > >> > > > > > > >
> > > > >> > > > > > > > https://twitter.com/snntrable
> > > > >> > > > > > > >
> > > > >> > > > > > > > https://github.com/knaufk
> > > > >> > > > > > > >
> > > > >> > > > > > >
> > > > >> > > > > >
> > > > >> > > > >
> > > > >> > > >
> > > > >> > >
> > > > >> > >
> > > > >> > > --
> > > > >> > >
> > > > >> > > Konstantin Knauf
> > > > >> > >
> > > > >> > > https://twitter.com/snntrable
> > > > >> > >
> > > > >> > > https://github.com/knaufk
> > > > >> > >
> > > > >> >
> > > > >>
> > > > >
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Becket Qin <be...@gmail.com>.
Hi Till,
Thanks for the comments and questions. To be clear, I am not saying that
the side-input stream does not work for the dynamic pattern update use
case. But I think OC is a better solution. The design goal for CEP dynamic
pattern is not only make it work, but also make it user friendly and
extensible. So as a user, I expect the following:
- Use CEP with dynamic pattern update without depending on external
systems. e.g. updating the pattern by directly talking to the Flink job
itself.
- Some sort of isolation between patterns. e.g. a pattern update failure
won't cause other running patterns to fail.
- Easy to query the currently running patterns in the Flink job.
- Extensible to add new features. e.g. apply some pattern to a subset of
subtasks. Disable dynamic pattern update during a service window, etc.
It looks to me that OC is a more promising way to to achieve the above.
Please also see the reply to your questions inline below.
> You mentioned that a TM might find out that a pattern is invalid and then
> it could use the 2-way communication with the JM to tell the other TMs that
> the pattern is invalid. How exactly would a TM detect that a pattern is
> invalid at data processing time? And assuming that this is possible for a
> single TM, why can't the other TMs not detect this problem? Is it because
> the validity of patterns might depend on data that is different between
> TMs?
Yes, the TMs are processing different records, so some may encounter issue
while others are running fine, for example, a field may be missing from a
record while the pattern requires it. Even if all the TMs have detected the
problem, without a channel to report back the issue, the only thing TMs can
do is either to throw exception and stop processing.
You also mentioned that deep-learning-on-flink could benefit from an OC
> control plane but I couldn't find the referenced link. Would
> deep-learning-on-flink like to use OCs as a kind of parameter server? Could
> you elaborate on deep-learning-on-flink's usage of such a feature?
deep-learning-on-flink[1] has a general ML cluster abstraction that can run
TF / PyTorch etc. This cluster has a ML master role to manage the
liveliness of all the ML workers which are python processes running
side-by-side with TMs. The ML workers can be PS or Worker of TensorFlow.
For example, if 10 TF worker and 5 TF PS nodes are needed, a Flink UDF
operator of parallelism 10 and a Flink Source operator with parallelism = 5
will be created to run the TF worker and TF PS respectively. All the 15
nodes running either PS or Worker are managed by the ML master. Prior to
OC, the implementation was having a Source operator with parallelism = 1 to
run the master; let the ML workers register themselves to the an external
ZK so the master can discover them. So basically users have to build their
own control plane. With OC, at very least, we no longer need ZK anymore.
Concerning reprocessing command history and repeatable processing results I
> think there is actually quite a big difference between using a Flink source
> vs. offering a REST server that can receive command that are distributed
> via the OCs. In the former case we can rely on the external system to
> persist commands whereas in the latter approach we/users have to implement
> a storage solution on their own (in the simplest case users will probably
> store everything in state which might grow indefinitely if stored as a
> changelog).
It is true that a Flink Source is easier to provide a change log of
patterns. But there are also downsides. The most prominent one is that in
order to update the dynamic pattern, users have to run an external system
for the source to read. Or users have to implement a REST Source taking
command directly like a web server. In that case, the service discovery is
again a problem and needs external dependency.
On the other hand, it is not so difficult for OC to store a change log
history. Assuming there are 100 pattern updates / day for a CEP job and one
year of history should be stored. Let's say each pattern change log entry
is 1K bytes. The pattern update change log for the entire year is just 34
MB, which seems quite small. And users can also query the patterns in
effect via the same endpoint. I think this would provide a good out-of-box
experience in the vast majority of cases. No external dependencies and a
single REST endpoint. In rare cases where there is a large amount of
pattern update log. External systems can still be leveraged. One potential
issue might be that a command that has been received but not checkpointed
yet may got lost if the job fails over. This can be mitigated by allowing
OC to ask JM to trigger a checkpoint (not there yet but may worth
thinking), or simply introduce a *PendingCommit* state for a pattern
indicating it's not committed yet. In the worst case, we can always
fallback to store patterns in external systems such as a database.
Thanks,
Jiangjie (Becket) Qin
[1]
https://github.com/flink-extended/dl-on-flink/tree/master/deep-learning-on-flink
On Tue, Jan 4, 2022 at 4:45 PM Till Rohrmann <tr...@apache.org> wrote:
> Hi Becket,
>
> Thanks for the explanation. While I do agree that a general 2-way
> communication pattern would be nice to have, I also believe that this
> approach is probably at least one magnitude more complex to realize than
> the side-input approach. Therefore, I really would like to understand why
> such a mechanism is required for the CEP use case.
>
> You mentioned that a TM might find out that a pattern is invalid and then
> it could use the 2-way communication with the JM to tell the other TMs that
> the pattern is invalid. How exactly would a TM detect that a pattern is
> invalid at data processing time? And assuming that this is possible for a
> single TM, why can't the other TMs not detect this problem? Is it because
> the validity of patterns might depend on data that is different between
> TMs?
>
> You also mentioned that deep-learning-on-flink could benefit from an OC
> control plane but I couldn't find the referenced link. Would
> deep-learning-on-flink like to use OCs as a kind of parameter server? Could
> you elaborate on deep-learning-on-flink's usage of such a feature?
>
> Concerning reprocessing command history and repeatable processing results I
> think there is actually quite a big difference between using a Flink source
> vs. offering a REST server that can receive command that are distributed
> via the OCs. In the former case we can rely on the external system to
> persist commands whereas in the latter approach we/users have to implement
> a storage solution on their own (in the simplest case users will probably
> store everything in state which might grow indefinitely if stored as a
> changelog).
>
> Cheers,
> Till
>
> On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com> wrote:
>
> > Hi David,
> >
> > Thanks for sharing your thoughts. Some quick reply to your comments:
> >
> > We're still talking about the "web server based"
> > > pattern_processor_discoverer, but what about other use cases? One of my
> > big
> > > concerns is that user's can not really reuse any part of the Flink
> > > ecosystem to implement the discovery logic. For example if they want to
> > > read patterns from Kafka topic, they need to roll their own discoverer
> > > based on the vanilla Kafka client. If we're talking about
> extensibility,
> > > should we also make sure that the existing primitives can be reused?
> >
> >
> > KafkaSource is actually more complicated than vanilla KafkaConsumer from
> > the perspective of consuming Kafka messages. The KafkaSource just helps
> > make it easier for Flink jobs to process these messages. In fact,
> > KafkaConsumer is more powerful than KafkaSource in terms of talking to
> > Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator] and
> > [KafkaSource + side-input], not [KafkaConsumer + side-input].
> >
> > This can be done for the side-input as well by filtering invalid patterns
> > > before the broadcast. You can also send the invalid patterns to any
> side
> > > output you want. I have a feeling that we're way too attached to the
> REST
> > > server use case in this discussion. I agree that for that case, this
> > > solution is the most straightforward one.
> >
> >
> > Depending on whether the invalidity is discovered in pattern definition
> > time or data processing time. e.g. A valid pattern with invalid data
> which
> > fails to process can only be detected in data processing time. So the
> > pattern won't be filtered out before the broadcast.
> >
> > I agree that 2-way communication in the "data-flow like" API is tricky,
> > > because it requires cycles / iterations, which are still not really
> > solved
> > > (for a good reason, it's really tough nut to crack). This makes me
> think
> > > that the OC may be bit of a "incomplete" workaround for not having
> fully
> > > working support for iterations.
> >
> >
> > For example I'm not really confident that the checkpointing of the OC
> works
> > > correctly right now, because it doesn't seem to require checkpoint
> > barrier
> > > alignment as the regular stream inputs. We also don't have a proper
> > support
> > > for watermarking (this is again tricky, because of the cycle).
> >
> >
> > If we decide to go down this road, should we first address some of these
> > > limitations?
> >
> > I agree. OC is proven to be useful and we should think about how to
> enhance
> > it instead of not using it.
> >
> > If I understand that correctly, this means only the LATEST state of the
> > > patterns (in other words - patterns that are currently in use). Is this
> > > really sufficient for historical re-processing? Can someone for example
> > > want re-process the data in more of a "temporal join" fashion? Also
> AFAIK
> > > historical processing in combination with "coordinator checkpoints" is
> > not
> > > really something that we currently support of the box, are there any
> > plans
> > > on tackling this (my other concern is that this should not go against
> the
> > > "unified batch & stream processing" efforts)?
> >
> > I think in this case, the state would contain the entire pattern update
> > history. Not the final state, but the change log. In fact, it is not
> > possible to guarantee the correct result unless you have the entire
> change
> > log. Even with side-input, there still could be late arrivals in the
> > pattern update stream, and the only way to correct it is to either have
> all
> > the data reprocessed (with all the pattern change log loaded upfront) or
> > having retraction support.
> >
> > I can imagine that if this should be a concern, we could move the
> execution
> > > of the OC to the task managers. This also makes me thing, that we
> > shouldn't
> > > make any strong assumptions that the OC will always run in the
> JobManager
> > > (this is especially relevant for the embedded web-server use case).
> >
> > This is a very good point. I think we should do this. The reason OC is in
> > JM is based on the assumption that control plane usually have little
> > traffic. But if that is not the case, we should move the OC out of JM,
> > maybe to TM.
> >
> >
> >
> > I think the key topic we are discussing is what the Flink control plane
> > should look like, and CEP is just an example use case. There are
> basically
> > two options:
> >
> > 1. Using the side-input / broadcast stream
> > 2. Using the OperatorCoordinator.
> >
> > Although we are having this discussion under the context of supporting
> CEP
> > dynamic pattern update, it would be really helpful to reach agreement on
> > the design principle in general of how Flink should handle similar
> external
> > control demands, a.k.a how to provide a decent control plane in Flink to
> > the users.
> >
> > Here is my take on these two options, based on the requirements of a
> > control plane.
> >
> > *Communication Requirements*
> > Flink has two kinds of control planes - in-band and out-of-band.
> > In-band control plane is like watermark and checkpoint marker. It
> requires
> > the entire DAG to be in a consistent state, so the control messages flow
> > with the data in one direction. This is a one-way control flow.
> > Examples of out-of-band control plane is OC and JM/TM communication. They
> > do not require a global consistency or awareness across the entire DAG.
> >
> > Before OC, neither of these two kinds of control plain was exposed to the
> > users. OC allows the users to leverage the out-of-band control plane so
> > they can coordinate across subtasks. This is a more widely used control
> > flow from user defined operator perspective which requires 2-way
> > communication.
> >
> > - side-input stream is one-way communication. Moreover, I don't think
> > iteration is the right way to address this. Unlike the abstraction of
> > data
> > processing which is a DAG, the control plane may require communication
> > between arbitrary two operators in different orders. Using iterations
> > may
> > end up with an explosion of feedback edges that are not only
> > complicated to
> > express, but also hard to debug and maintain.
> > - OC provides a decent 2-way communication mechanism.
> >
> >
> > *Cost for low traffic use case*
> > An important difference between data channel and control channel is
> traffic
> > pattern. Unlike data plane, the control plane is usually idle for the
> vast
> > majority of the time with occasional control messages.
> >
> > - One argument to use the side-input / broadcast stream was that users
> > can reuse the existing connectors. However, most Flink sources are
> > designed
> > to handle large throughput of traffic that maintains all the threads,
> > network connections, etc. Not to say the external resources such as
> > Kafka
> > topics to store the commands.
> > - OC can have a much lower constant cost.
> >
> >
> > *Easy to use*
> > Personally speaking, I think the most simple and user-friendly interface
> is
> > a REST API that accepts control commands.
> >
> > - One proposal at this point is to have a separate web server
> > independent of the Flink job. In that case, should users implement
> that
> > web
> > server? In order to pass the command to the Flink job, does that mean
> > users
> > should implement a Flink source that can read the commands from the
> web
> > server? Or the web server would send the command to something like
> Kafka
> > and let the Flink side-input read from there. There seems to be a lot
> > for
> > the users to do. And it seems an unnecessarily complicated system to
> > build
> > to send occasional control messages to a Flink job.
> > - OC can simply be reached via the JM REST API.
> > - e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> > <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx> would simply
> > send the Content to the OC of OP_NAME.
> >
> > *Work well with checkpoints*
> >
> > - side-input streams works well with checkpoint, thanks to its
> > compatibility to the DAG abstraction.
> > - The OperatorCoordinator requires more careful design to work well
> with
> > checkpoints. The complexity mostly comes from the 2-way communication.
> > At
> > this point the OperatorCoordinator message delivery semantic may not
> be
> > as
> > robust as side-input streams. However, I think this is mainly due to
> > potential bugs in implementation instead of fundamental design
> problems.
> > Basically the checkpoint semantic should be:
> > - The JM will first checkpoint all the OperatorCoordinator, more
> > specifically for each OperatorCoordinator,
> > - 1) JM blocks the input queue to stop receiving new events from
> > the subtasks.
> > - 2) let all the operator coordinator finish processing all the
> > pending events in the OC input queue.
> > - 3) flush the OC output queue until all the events sent are
> > acknowledged.
> > - 3) unblock the input queue, but block the output queue until
> all
> > the subtasks of the OC finish checkpoints.
> > - The JM starts a normal checkpoint starting from the Source.
> > - If an operator has a coordinator, and it has sent some events
> to
> > the OC but has not been acknowledged. These events need to be
> > put into the
> > subtasks' checkpoint.
> > - After all the subtasks of an operator finishes checkpoint, the
> > output queue of the corresponding OC can be unblocked.
> > It looks that the above protocol would let OC have a clear checkpoint
> > semantic. And this complexity seems must for 2-way communication. I
> > think
> > we are able to hide the above protocol from users by having an
> abstract
> > OC
> > implementation.
> >
> >
> > *Reprocess command history and repeatable processing results*
> > This seems not something generally required for a control plane. But if
> the
> > control plane changes the data processing behavior, there might be some
> use
> > case. Just like the CEP pattern update. In order to do this, users will
> > need to provide a full command history to the operators. That consists of
> > two steps:
> >
> > 1. get the full command history. (Flink Source V.S. Custom way to
> > retrieve command history.)
> > 2. send them to the operators. (Side-input V.S. OC/Operator
> > communication)l
> >
> > I actually don't feel much difference between these two options. I am not
> > sure if a Flink source is necessarily simpler than the user implemented
> > logic. For example, if all the changes are just written in a database
> > table. From the user's perspective, I feel fine with querying the DB by
> > myself using something like JDBC (or use KafkaConsumer to read the
> pattern
> > history from a Kafka topic) and send all the pattern change history to
> the
> > operators before they start to process the actual events.
> >
> > *Stability impact to the Flink Job*
> > I agree this is a valid concern. There is only one JM and currently OC
> runs
> > there, which may potentially cause JM crash and result in job failure.
> > Running in TM may have a less impact. So I think it makes sense to run OC
> > in TM. However, this is more of how we can implement OC to make it more
> > robust. It does not forfeit the other semantic and user experience
> benefits
> > mentioned above.
> >
> >
> > To sum up:
> > 1. Regardless of whether CEP chooses OC or side-input stream, a decent
> > 2-way communication control plane seems really helpful and has been
> proven
> > by quite a few existing use cases. To me the question is how to make it
> > more robust, not whether we should use it or not.
> > 2. As for CEP, if we assume OC will be robust enough, personally I feel
> OC
> > is a better fit than side-input mainly because of the simplicity and
> > extensibility.
> >
> > Thanks,
> >
> > Jiangjie (Becket) Qin
> >
> >
> > On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org> wrote:
> >
> > > Hi all,
> > >
> > > sorry for the late reply, vacation season ;) I'm still not 100% sold on
> > > choosing the OC for this use-case, but on the other hand I don't have
> > > strong arguments against it. Few more questions / thoughts:
> > >
> > > We're still talking about the "web server based"
> > > pattern_processor_discoverer, but what about other use cases? One of my
> > big
> > > concerns is that user's can not really reuse any part of the Flink
> > > ecosystem to implement the discovery logic. For example if they want to
> > > read patterns from Kafka topic, they need to roll their own discoverer
> > > based on the vanilla Kafka client. If we're talking about
> extensibility,
> > > should we also make sure that the existing primitives can be reused?
> > >
> > > For instance, the example I gave in my previous email seems not easily
> > > > achievable with side-input / broadcast streams: a single invalid
> > pattern
> > > > detected on a TM can be disabled elegantly globally without crashing
> > the
> > > > entire Flink job.
> > >
> > >
> > > This can be done for the side-input as well by filtering invalid
> patterns
> > > before the broadcast. You can also send the invalid patterns to any
> side
> > > output you want. I have a feeling that we're way too attached to the
> REST
> > > server use case in this discussion. I agree that for that case, this
> > > solution is the most straightforward one.
> > >
> > > OC is a 2-way communication mechanism, i.e. a subtask can also send
> > > > OperatorEvent to the coordinator to report its owns status, so that
> the
> > > > coordinator can act accordingly.
> > > >
> > >
> > > I agree that 2-way communication in the "data-flow like" API is tricky,
> > > because it requires cycles / iterations, which are still not really
> > solved
> > > (for a good reason, it's really tough nut to crack). This makes me
> think
> > > that the OC may be bit of a "incomplete" workaround for not having
> fully
> > > working support for iterations.
> > >
> > > For example I'm not really confident that the checkpointing of the OC
> > works
> > > correctly right now, because it doesn't seem to require checkpoint
> > barrier
> > > alignment as the regular stream inputs. We also don't have a proper
> > support
> > > for watermarking (this is again tricky, because of the cycle).
> > >
> > > If we decide to go down this road, should we first address some of
> these
> > > limitations?
> > >
> > > OperatorCoordinator will checkpoint the full amount of PatternProcessor
> > > > data. For the reprocessing of historical data, you can read the
> > > > PatternProcessor snapshots saved by this checkpoint from a certain
> > > > historical checkpoint, and then recreate the historical data through
> > > these
> > > > PatternProcessor snapshots.
> > > >
> > >
> > > If I understand that correctly, this means only the LATEST state of the
> > > patterns (in other words - patterns that are currently in use). Is this
> > > really sufficient for historical re-processing? Can someone for example
> > > want re-process the data in more of a "temporal join" fashion? Also
> AFAIK
> > > historical processing in combination with "coordinator checkpoints" is
> > not
> > > really something that we currently support of the box, are there any
> > plans
> > > on tackling this (my other concern is that this should not go against
> the
> > > "unified batch & stream processing" efforts)?
> > >
> > > I do agree that having the user defined control logic defined in the JM
> > > > increases the chance of instability.
> > > >
> > >
> > > I can imagine that if this should be a concern, we could move the
> > execution
> > > of the OC to the task managers. This also makes me thing, that we
> > shouldn't
> > > make any strong assumptions that the OC will always run in the
> JobManager
> > > (this is especially relevant for the embedded web-server use case).
> > >
> > > If an agreement is reached on OperatorCoodinator, I will start the
> voting
> > > > thread.
> > > >
> > >
> > > As for the vote, I'd would be great if we can wait until the next week
> as
> > > many people took vacation until end of the year.
> > >
> > > Overall, I really like the feature, this will be a great addition to
> > Flink.
> > >
> > > Best,
> > > D.
> > >
> > >
> > >
> > > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <martijn@ververica.com
> >
> > > wrote:
> > >
> > > > Hi all,
> > > >
> > > > I can understand the need for a control plane mechanism. I'm not the
> > > > technical go-to person for questions on the OperatorCoordinator, but
> I
> > > > would expect that we could offer those interfaces from Flink but
> > > shouldn't
> > > > recommend running user-code in the JobManager itself. I think the
> user
> > > code
> > > > (like a webserver) should run outside of Flink (like via a sidecar)
> and
> > > use
> > > > only the provided interfaces to communicate.
> > > >
> > > > I would like to get @David Morávek <dm...@apache.org> opinion on the
> > > > technical part.
> > > >
> > > > Best regards,
> > > >
> > > > Martijn
> > > >
> > > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <
> nicholasjiang@apache.org
> > >
> > > > wrote:
> > > >
> > > >> Hi Konstantin, Becket, Martijn,
> > > >>
> > > >> Thanks for sharing your feedback. What other concerns do you have
> > about
> > > >> OperatorCoodinator? If an agreement is reached on
> OperatorCoodinator,
> > I
> > > >> will start the voting thread.
> > > >>
> > > >> Best,
> > > >> Nicholas Jiang
> > > >>
> > > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > > >> > Hi Konstantin,
> > > >> >
> > > >> > Thanks for sharing your thoughts. Please see the reply inline
> below.
> > > >> >
> > > >> > Thanks,
> > > >> >
> > > >> > Jiangjie (Becket) Qin
> > > >> >
> > > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <
> knaufk@apache.org
> > >
> > > >> wrote:
> > > >> >
> > > >> > > Hi Becket, Hi Nicholas,
> > > >> > >
> > > >> > > Thanks for joining the discussion.
> > > >> > >
> > > >> > > 1 ) Personally, I would argue that we should only run user code
> in
> > > the
> > > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems wrong to
> me
> > to
> > > >> > > encourage users to e.g. run a webserver on the Jobmanager, or
> > > >> continuously
> > > >> > > read patterns from a Kafka Topic on the Jobmanager, but both of
> > > these
> > > >> I see
> > > >> > > happening with the current design. We've had lots of issues with
> > > >> > > classloading leaks and other stability issues on the Jobmanager
> > and
> > > >> making
> > > >> > > this more complicated, if there is another way, seems
> unnecessary.
> > > >> >
> > > >> >
> > > >> > I think the key question here is what primitive does Flink provide
> > to
> > > >> > facilitate the user implementation of their own control logic /
> > > control
> > > >> > plane? It looks that previously, Flink assumes that all the user
> > logic
> > > >> is
> > > >> > just data processing logic without any control / coordination
> > > >> requirements.
> > > >> > However, it turns out that a decent control plane abstraction is
> > > >> required
> > > >> > in association with the data processing logic in many cases,
> > including
> > > >> > Source / Sink and other user defined operators in general. The
> fact
> > > >> that we
> > > >> > ended up with adding the SplitEnumerator and GlobalCommitter are
> > just
> > > >> two
> > > >> > examples of the demand of such coordination among user defined
> > logics.
> > > >> > There are other cases that we see in ecosystem projects, such as
> > > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > > >> >
> > > >> > Such control plane primitives are critical to the extensibility
> of a
> > > >> > project. If we look at other projects, exposing such control plane
> > > >> logic is
> > > >> > quite common. For example, Hadoop ended up with exposing YARN as a
> > > >> public
> > > >> > API to the users, which is extremely popular. Kafka consumers
> > exposed
> > > >> the
> > > >> > consumer group rebalance logic to the users via
> > > >> ConsumerPartitionAssigner,
> > > >> > which is also a control plane primitive.
> > > >> >
> > > >> > To me it is more important to think about how we can improve the
> > > >> stability
> > > >> > of such a control plane mechanism, instead of simply saying no to
> > the
> > > >> users.
> > > >> >
> > > >> >
> > > >> >
> > > >> >
> > > >> > > 2) In addition, I suspect that, over time we will have to
> > implement
> > > >> all the
> > > >> > > functionality that regular sources already provide around
> > > consistency
> > > >> > > (watermarks, checkpointing) for the PatternProcessorCoordinator,
> > > too.
> > > >> >
> > > >> >
> > > >> > I think OperatorCoordinator should have a generic communication
> > > >> mechanism
> > > >> > for all the operators, not specific to Source. We should probably
> > have
> > > >> an
> > > >> > AbstractOperatorCoordinator help dealing with the communication
> > layer,
> > > >> and
> > > >> > leave the state maintenance and event handling logic to the user
> > code.
> > > >> >
> > > >> >
> > > >> > > 3) I understand that running on the Jobmanager is easier if you
> > want
> > > >> to
> > > >> > > launch a REST server directly. Here my question would be: does
> > this
> > > >> really
> > > >> > > need to be solved inside of Flink or couldn't you start a
> > webserver
> > > >> next to
> > > >> > > Flink? If we start using the Jobmanager as a REST server users
> > will
> > > >> expect
> > > >> > > that e.g. it is highly available and can be load balanced and we
> > > >> quickly
> > > >> > > need to think about aspects that we never wanted to think about
> in
> > > the
> > > >> > > context of a Flink Jobmanager.
> > > >> > >
> > > >> >
> > > >> > I think the REST API is just for receiving commands targeting a
> > > running
> > > >> > Flink job. If the job fails, the REST API would be useless.
> > > >> >
> > > >> >
> > > >> > > So, can you elaborate a bit more, why a side-input/broadcast
> > stream
> > > is
> > > >> > >
> > > >> > > a) more difficult
> > > >> > > b) has vague semantics (To me semantics of a stream-stream seem
> > > >> clearer
> > > >> > > when it comes to out-of-orderness, late data, reprocessing or
> > batch
> > > >> > > execution mode.)
> > > >> >
> > > >> >
> > > >> > I do agree that having the user defined control logic defined in
> the
> > > JM
> > > >> > increases the chance of instability. In that case, we may think of
> > > other
> > > >> > solutions and I am fully open to that. But the side-input /
> > broadcast
> > > >> > stream seems more like a bandaid instead of a carefully designed
> > > control
> > > >> > plane mechanism.
> > > >> >
> > > >> > A decent control plane requires two-way communication, so
> > information
> > > >> can
> > > >> > be reported / collected from the entity being controlled, and the
> > > >> > coordinator / controller can send decisions or commands to the
> > > entities
> > > >> > accordingly, just like our TM / JM communication. IIUC, this is
> not
> > > >> > achievable with the existing side-input / broadcast stream as both
> > of
> > > >> them
> > > >> > are one-way communication mechanisms. For instance, the example I
> > gave
> > > >> in
> > > >> > my previous email seems not easily achievable with side-input /
> > > >> broadcast
> > > >> > streams: a single invalid pattern detected on a TM can be disabled
> > > >> > elegantly globally without crashing the entire Flink job.
> > > >> >
> > > >> >
> > > >> > > Cheers,
> > > >> > >
> > > >> > > Konstantin
> > > >> > >
> > > >> > >
> > > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <
> becket.qin@gmail.com
> > >
> > > >> wrote:
> > > >> > >
> > > >> > > > Hi folks,
> > > >> > > >
> > > >> > > > I just finished reading the previous emails. It was a good
> > > >> discussion.
> > > >> > > Here
> > > >> > > > are my two cents:
> > > >> > > >
> > > >> > > > *Is OperatorCoordinator a public API?*
> > > >> > > > Regarding the OperatorCoordinator, although it is marked as
> > > internal
> > > >> > > > interface at this point, I intended to make it a public
> > interface
> > > >> when
> > > >> > > add
> > > >> > > > that in FLIP-27. This is a powerful cross-subtask
> communication
> > > >> mechanism
> > > >> > > > that enables many use cases, Source / Sink / TF on Flink / CEP
> > > here
> > > >> > > again.
> > > >> > > > To my understanding, OC was marked as internal because we
> think
> > it
> > > >> is not
> > > >> > > > stable enough yet. We may need to fortify the OperatorEvent
> > > delivery
> > > >> > > > semantic a little bit so it works well with checkpoint in
> > general.
> > > >> > > >
> > > >> > > > I think it is a valid concern that user code running in JM may
> > > cause
> > > >> > > > instability. However, not providing this communication
> mechanism
> > > >> only
> > > >> > > makes
> > > >> > > > a lot of use case even harder to implement. So it seems that
> > > having
> > > >> the
> > > >> > > OC
> > > >> > > > exposed to end users brings more benefits than harm to Flink.
> At
> > > >> the end
> > > >> > > of
> > > >> > > > the day, users have many ways to crash a Flink job if they do
> > not
> > > >> write
> > > >> > > > proper code. So making those who know what they do happy seems
> > > more
> > > >> > > > important here.
> > > >> > > >
> > > >> > > > *OperatorCoordinator V.S. side-input / broadcast stream*
> > > >> > > > I think both of them can achieve the goal of dynamic patterns.
> > The
> > > >> main
> > > >> > > > difference is the extensibility.
> > > >> > > >
> > > >> > > > OC is a 2-way communication mechanism, i.e. a subtask can also
> > > send
> > > >> > > > OperatorEvent to the coordinator to report its owns status, so
> > > that
> > > >> the
> > > >> > > > coordinator can act accordingly. This is sometimes useful. For
> > > >> example, a
> > > >> > > > single invalid pattern can be disabled elegantly without
> > crashing
> > > >> the
> > > >> > > > entire Flink job. In the future, if we allow users to send
> > > external
> > > >> > > command
> > > >> > > > to OC via JM, a default self-contained implementation can just
> > > >> update the
> > > >> > > > pattern via the REST API without external dependencies.
> > > >> > > >
> > > >> > > > Another reason I personally prefer OC is because it is an
> > explicit
> > > >> > > control
> > > >> > > > plain mechanism, where as the side-input / broadcast stream
> has
> > > are
> > > >> more
> > > >> > > > vague semantic.
> > > >> > > >
> > > >> > > > Thanks,
> > > >> > > >
> > > >> > > > Jiangjie (Becket) Qin
> > > >> > > >
> > > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <
> dmvk@apache.org>
> > > >> wrote:
> > > >> > > >
> > > >> > > > > Hi Yunfeng,
> > > >> > > > >
> > > >> > > > > thanks for drafting this FLIP, this will be a great addition
> > > into
> > > >> the
> > > >> > > CEP
> > > >> > > > > toolbox!
> > > >> > > > >
> > > >> > > > > Apart from running user code in JM, which want to avoid in
> > > >> general, I'd
> > > >> > > > > have one more another concern about using the
> > > OperatorCoordinator
> > > >> and
> > > >> > > > that
> > > >> > > > > is re-processing of the historical data. Any thoughts about
> > how
> > > >> this
> > > >> > > will
> > > >> > > > > work with the OC?
> > > >> > > > >
> > > >> > > > > I have a slight feeling that a side-input (custom source /
> > > >> operator +
> > > >> > > > > broadcast) would a better fit for this case. This would
> > simplify
> > > >> the
> > > >> > > > > consistency concerns (watermarks + pushback) and the
> > > >> re-processing of
> > > >> > > > > historical data.
> > > >> > > > >
> > > >> > > > > Best,
> > > >> > > > > D.
> > > >> > > > >
> > > >> > > > >
> > > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > > >> > > nicholasjiang@apache.org
> > > >> > > > >
> > > >> > > > > wrote:
> > > >> > > > >
> > > >> > > > > > Hi Konstantin, Martijn
> > > >> > > > > >
> > > >> > > > > > Thanks for the detailed feedback in the discussion. What I
> > > >> still have
> > > >> > > > > left
> > > >> > > > > > to answer/reply to:
> > > >> > > > > >
> > > >> > > > > > -- Martijn: Just to be sure, this indeed would mean that
> if
> > > for
> > > >> > > > whatever
> > > >> > > > > > reason the heartbeat timeout, it would crash the job,
> right?
> > > >> > > > > >
> > > >> > > > > > IMO, if for whatever reason the heartbeat timeout, it
> > couldn't
> > > >> check
> > > >> > > > the
> > > >> > > > > > PatternProcessor consistency between the
> OperatorCoordinator
> > > >> and the
> > > >> > > > > > subtasks so that the job would be crashed.
> > > >> > > > > >
> > > >> > > > > > -- Konstantin: What I was concerned about is that we
> > basically
> > > >> let
> > > >> > > > users
> > > >> > > > > > run a UserFunction in the OperatorCoordinator, which it
> does
> > > >> not seem
> > > >> > > > to
> > > >> > > > > > have been designed for.
> > > >> > > > > >
> > > >> > > > > > In general, we have reached an agreement on the design of
> > this
> > > >> FLIP,
> > > >> > > > but
> > > >> > > > > > there are some concerns on the OperatorCoordinator, about
> > > >> whether
> > > >> > > > > basically
> > > >> > > > > > let users run a UserFunction in the OperatorCoordinator is
> > > >> designed
> > > >> > > for
> > > >> > > > > > OperatorCoordinator. We would like to invite Becket Qin
> who
> > is
> > > >> the
> > > >> > > > author
> > > >> > > > > > of OperatorCoordinator to help us to answer this concern.
> > > >> > > > > >
> > > >> > > > > > Best,
> > > >> > > > > > Nicholas Jiang
> > > >> > > > > >
> > > >> > > > > >
> > > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > > >> > > > > > > Hi all,
> > > >> > > > > > >
> > > >> > > > > > > Really like the discussion on this topic moving
> forward. I
> > > >> really
> > > >> > > > think
> > > >> > > > > > > this feature will be much appreciated by the Flink
> users.
> > > >> What I
> > > >> > > > still
> > > >> > > > > > have
> > > >> > > > > > > left to answer/reply to:
> > > >> > > > > > >
> > > >> > > > > > > -- Good point. If for whatever reason the different
> > > >> taskmanagers
> > > >> > > > can't
> > > >> > > > > > get
> > > >> > > > > > > the latest rule, the Operator Coordinator could send a
> > > >> heartbeat to
> > > >> > > > all
> > > >> > > > > > > taskmanagers with the latest rules and check the
> heartbeat
> > > >> response
> > > >> > > > > from
> > > >> > > > > > > all the taskmanagers whether the latest rules of the
> > > >> taskmanager is
> > > >> > > > > equal
> > > >> > > > > > > to these of the Operator Coordinator.
> > > >> > > > > > >
> > > >> > > > > > > Just to be sure, this indeed would mean that if for
> > whatever
> > > >> reason
> > > >> > > > the
> > > >> > > > > > > heartbeat timeout, it would crash the job, right?
> > > >> > > > > > >
> > > >> > > > > > > -- We have consided about the solution mentioned above.
> In
> > > >> this
> > > >> > > > > > solution, I
> > > >> > > > > > > have some questions about how to guarantee the
> consistency
> > > of
> > > >> the
> > > >> > > > rule
> > > >> > > > > > > between each TaskManager. By having a coodinator in the
> > > >> JobManager
> > > >> > > to
> > > >> > > > > > > centrally manage the latest rules, the latest rules of
> all
> > > >> > > > TaskManagers
> > > >> > > > > > are
> > > >> > > > > > > consistent with those of the JobManager, so as to avoid
> > the
> > > >> > > > > > inconsistencies
> > > >> > > > > > > that may be encountered in the above solution. Can you
> > > >> introduce
> > > >> > > how
> > > >> > > > > this
> > > >> > > > > > > solution guarantees the consistency of the rules?
> > > >> > > > > > >
> > > >> > > > > > > The consistency that we could guarantee was based on how
> > > >> often each
> > > >> > > > > > > TaskManager would do a refresh and how often we would
> > > accept a
> > > >> > > > refresh
> > > >> > > > > to
> > > >> > > > > > > fail. We set the refresh time to a relatively short one
> > (30
> > > >> > > seconds)
> > > >> > > > > and
> > > >> > > > > > > maximum failures to 3. That meant that we could
> guarantee
> > > that
> > > >> > > rules
> > > >> > > > > > would
> > > >> > > > > > > be updated in < 2 minutes or else the job would crash.
> > That
> > > >> was
> > > >> > > > > > sufficient
> > > >> > > > > > > for our use cases. This also really depends on how big
> > your
> > > >> cluster
> > > >> > > > > is. I
> > > >> > > > > > > can imagine that if you have a large scale cluster that
> > you
> > > >> want to
> > > >> > > > > run,
> > > >> > > > > > > you don't want to DDOS the backend system where you have
> > > your
> > > >> rules
> > > >> > > > > > stored.
> > > >> > > > > > >
> > > >> > > > > > > -- In summary, the current design is that JobManager
> tells
> > > all
> > > >> > > > > > TaskManagers
> > > >> > > > > > > the latest rules through OperatorCoodinator, and will
> > > >> initiate a
> > > >> > > > > > heartbeat
> > > >> > > > > > > to check whether the latest rules on each TaskManager
> are
> > > >> > > consistent.
> > > >> > > > > We
> > > >> > > > > > > will describe how to deal with the Failover scenario in
> > more
> > > >> detail
> > > >> > > > on
> > > >> > > > > > FLIP.
> > > >> > > > > > >
> > > >> > > > > > > Thanks for that. I think having the JobManager tell the
> > > >> > > TaskManagers
> > > >> > > > > the
> > > >> > > > > > > applicable rules would indeed end up being the best
> > design.
> > > >> > > > > > >
> > > >> > > > > > > -- about the concerns around consistency raised by
> > Martijn:
> > > I
> > > >> > > think a
> > > >> > > > > lot
> > > >> > > > > > > of those can be mitigated by using an event time
> timestamp
> > > >> from
> > > >> > > which
> > > >> > > > > the
> > > >> > > > > > > rules take effect. The reprocessing scenario, for
> example,
> > > is
> > > >> > > covered
> > > >> > > > > by
> > > >> > > > > > > this. If a pattern processor should become active as
> soon
> > as
> > > >> > > > possible,
> > > >> > > > > > > there will still be inconsistencies between
> Taskmanagers,
> > > but
> > > >> "as
> > > >> > > > soon
> > > >> > > > > as
> > > >> > > > > > > possible" is vague anyway, which is why I think that's
> ok.
> > > >> > > > > > >
> > > >> > > > > > > I think an event timestamp is indeed a really important
> > one.
> > > >> We
> > > >> > > also
> > > >> > > > > used
> > > >> > > > > > > that in my previous role, with the
> ruleActivationTimestamp
> > > >> compared
> > > >> > > > to
> > > >> > > > > > > eventtime (well, actually we used Kafka logAppend time
> > > because
> > > >> > > > > > > eventtime wasn't always properly set so we used that
> time
> > to
> > > >> > > > overwrite
> > > >> > > > > > the
> > > >> > > > > > > eventtime from the event itself).
> > > >> > > > > > >
> > > >> > > > > > > Best regards,
> > > >> > > > > > >
> > > >> > > > > > > Martijn
> > > >> > > > > > >
> > > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> > > >> knaufk@apache.org>
> > > >> > > > > > wrote:
> > > >> > > > > > >
> > > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > > >> > > > > > > >
> > > >> > > > > > > > about the concerns around consistency raised by
> > Martijn: I
> > > >> think
> > > >> > > a
> > > >> > > > > lot
> > > >> > > > > > of
> > > >> > > > > > > > those can be mitigated by using an event time
> timestamp
> > > from
> > > >> > > which
> > > >> > > > > the
> > > >> > > > > > > > rules take effect. The reprocessing scenario, for
> > example,
> > > >> is
> > > >> > > > covered
> > > >> > > > > > by
> > > >> > > > > > > > this. If a pattern processor should become active as
> > soon
> > > as
> > > >> > > > > possible,
> > > >> > > > > > > > there will still be inconsistencies between
> > Taskmanagers,
> > > >> but "as
> > > >> > > > > soon
> > > >> > > > > > as
> > > >> > > > > > > > possible" is vague anyway, which is why I think that's
> > ok.
> > > >> > > > > > > >
> > > >> > > > > > > > about naming: The naming with "PatternProcessor"
> sounds
> > > >> good to
> > > >> > > me.
> > > >> > > > > > Final
> > > >> > > > > > > > nit: I would go for CEP#patternProccessors, which
> would
> > be
> > > >> > > > consistent
> > > >> > > > > > with
> > > >> > > > > > > > CEP#pattern.
> > > >> > > > > > > >
> > > >> > > > > > > > I am not sure about one of the rejected alternatives:
> > > >> > > > > > > >
> > > >> > > > > > > > > Have each subtask of an operator make the update on
> > > their
> > > >> own
> > > >> > > > > > > >
> > > >> > > > > > > > -
> > > >> > > > > > > >
> > > >> > > > > > > > It is hard to achieve consistency.
> > > >> > > > > > > > -
> > > >> > > > > > > >
> > > >> > > > > > > > Though the time interval that each subtask makes
> > the
> > > >> update
> > > >> > > > can
> > > >> > > > > > be
> > > >> > > > > > > > the same, the absolute time they make the update
> > > >> might be
> > > >> > > > > > different.
> > > >> > > > > > > > For
> > > >> > > > > > > > example, one makes updates at 10:00, 10:05, etc,
> > > while
> > > >> > > > another
> > > >> > > > > > does
> > > >> > > > > > > > it at
> > > >> > > > > > > > 10:01, 10:06. In this case the subtasks might
> > never
> > > >> > > > processing
> > > >> > > > > > data
> > > >> > > > > > > > with
> > > >> > > > > > > > the same set of pattern processors.
> > > >> > > > > > > >
> > > >> > > > > > > >
> > > >> > > > > > > > I would have thought that it is quite easy to poll for
> > the
> > > >> rules
> > > >> > > > from
> > > >> > > > > > each
> > > >> > > > > > > > Subtask at *about *the same time. So, this alone does
> > not
> > > >> seem to
> > > >> > > > be
> > > >> > > > > > > > enough to rule out this option. I've looped in David
> > > >> Moravek to
> > > >> > > get
> > > >> > > > > his
> > > >> > > > > > > > opinion of the additional load imposed on the JM.
> > > >> > > > > > > >
> > > >> > > > > > > > Thanks,
> > > >> > > > > > > >
> > > >> > > > > > > > Konstantin
> > > >> > > > > > > >
> > > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas Jiang <
> > > >> > > > > > nicholasjiang@apache.org>
> > > >> > > > > > > > wrote:
> > > >> > > > > > > >
> > > >> > > > > > > > > Hi Yue,
> > > >> > > > > > > > >
> > > >> > > > > > > > > Thanks for your feedback of the FLIP. I have
> addressed
> > > >> your
> > > >> > > > > > questions and
> > > >> > > > > > > > > made a corresponding explanation as follows:
> > > >> > > > > > > > >
> > > >> > > > > > > > > -- About Pattern Updating. If we use
> > > >> > > PatternProcessoerDiscoverer
> > > >> > > > to
> > > >> > > > > > > > update
> > > >> > > > > > > > > the rules, will it increase the load of JM? For
> > example,
> > > >> if the
> > > >> > > > > user
> > > >> > > > > > > > wants
> > > >> > > > > > > > > the updated rule to take effect immediately,, which
> > > means
> > > >> that
> > > >> > > we
> > > >> > > > > > need to
> > > >> > > > > > > > > set a shorter check interval or there is another
> > > scenario
> > > >> when
> > > >> > > > > users
> > > >> > > > > > > > rarely
> > > >> > > > > > > > > update the pattern, will the
> > PatternProcessoerDiscoverer
> > > >> be in
> > > >> > > > most
> > > >> > > > > > of
> > > >> > > > > > > > the
> > > >> > > > > > > > > time Do useless checks ? Will a lazy update mode
> could
> > > be
> > > >> used,
> > > >> > > > > > which the
> > > >> > > > > > > > > pattern only be updated when triggered by the user,
> > and
> > > do
> > > >> > > > nothing
> > > >> > > > > at
> > > >> > > > > > > > other
> > > >> > > > > > > > > times?
> > > >> > > > > > > > >
> > > >> > > > > > > > > PatternProcessoerDiscoverer is a user-defined
> > interface
> > > to
> > > >> > > > discover
> > > >> > > > > > the
> > > >> > > > > > > > > PatternProcessor updates. Periodically checking the
> > > >> > > > > PatternProcessor
> > > >> > > > > > in
> > > >> > > > > > > > the
> > > >> > > > > > > > > database is a implementation of the
> > > >> PatternProcessoerDiscoverer
> > > >> > > > > > > > interface,
> > > >> > > > > > > > > which is that periodically querys all the
> > > PatternProcessor
> > > >> > > table
> > > >> > > > in
> > > >> > > > > > > > certain
> > > >> > > > > > > > > interval. This implementation indeeds has the
> useless
> > > >> checks,
> > > >> > > and
> > > >> > > > > > could
> > > >> > > > > > > > > directly integrates the changelog of the table. In
> > > >> addition, in
> > > >> > > > > > addition
> > > >> > > > > > > > to
> > > >> > > > > > > > > the implementation of periodically checking the
> > > database,
> > > >> there
> > > >> > > > are
> > > >> > > > > > other
> > > >> > > > > > > > > implementations such as the PatternProcessor that
> > > provides
> > > >> > > > Restful
> > > >> > > > > > > > services
> > > >> > > > > > > > > to receive updates.
> > > >> > > > > > > > >
> > > >> > > > > > > > > -- I still have some confusion about how Key
> > Generating
> > > >> > > > Opertator
> > > >> > > > > > and
> > > >> > > > > > > > > CepOperator (Pattern Matching & Processing Operator)
> > > work
> > > >> > > > together.
> > > >> > > > > > If
> > > >> > > > > > > > > there are N PatternProcessors, will the Key
> Generating
> > > >> > > Opertator
> > > >> > > > > > > > generate N
> > > >> > > > > > > > > keyedStreams, and then N CepOperator would process
> > each
> > > >> Key
> > > >> > > > > > separately ?
> > > >> > > > > > > > Or
> > > >> > > > > > > > > every CepOperator Task would process all patterns,
> if
> > > so,
> > > >> does
> > > >> > > > the
> > > >> > > > > > key
> > > >> > > > > > > > type
> > > >> > > > > > > > > in each PatternProcessor need to be the same?
> > > >> > > > > > > > >
> > > >> > > > > > > > > Firstly the Pattern Matching & Processing Operator
> is
> > > not
> > > >> the
> > > >> > > > > > CepOperator
> > > >> > > > > > > > > at present, because CepOperator mechanism is based
> on
> > > the
> > > >> > > > NFAState.
> > > >> > > > > > > > > Secondly if there are N PatternProcessors, the Key
> > > >> Generating
> > > >> > > > > > Opertator
> > > >> > > > > > > > > combines all the keyedStreams with keyBy()
> operation,
> > > >> thus the
> > > >> > > > > > Pattern
> > > >> > > > > > > > > Matching & Processing Operator would process all the
> > > >> patterns.
> > > >> > > In
> > > >> > > > > > other
> > > >> > > > > > > > > words, the KeySelector of the PatternProcessor is
> used
> > > >> for the
> > > >> > > > Key
> > > >> > > > > > > > > Generating Opertator, and the Pattern and
> > > >> > > PatternProceessFunction
> > > >> > > > > of
> > > >> > > > > > the
> > > >> > > > > > > > > PatternProcessor are used for the Pattern Matching &
> > > >> Processing
> > > >> > > > > > Operator.
> > > >> > > > > > > > > Lastly the key type in each PatternProcessor is the
> > > same,
> > > >> > > > regarded
> > > >> > > > > as
> > > >> > > > > > > > > Object type.
> > > >> > > > > > > > >
> > > >> > > > > > > > > -- Maybe need to pay attention to it when
> implementing
> > > it
> > > >> .If
> > > >> > > > some
> > > >> > > > > > > > Pattern
> > > >> > > > > > > > > has been removed or updated, will the partially
> > matched
> > > >> results
> > > >> > > > in
> > > >> > > > > > > > > StateBackend would be clean up or We rely on state
> ttl
> > > to
> > > >> clean
> > > >> > > > up
> > > >> > > > > > these
> > > >> > > > > > > > > expired states.
> > > >> > > > > > > > >
> > > >> > > > > > > > > If certain Pattern has been removed or updated, the
> > > >> partially
> > > >> > > > > matched
> > > >> > > > > > > > > results in StateBackend would be clean up until the
> > next
> > > >> > > > > checkpoint.
> > > >> > > > > > The
> > > >> > > > > > > > > partially matched result doesn't depend on the state
> > ttl
> > > >> of the
> > > >> > > > > > > > > StateBackend.
> > > >> > > > > > > > >
> > > >> > > > > > > > > 4. Will the PatternProcessorManager keep all the
> > active
> > > >> > > > > > PatternProcessor
> > > >> > > > > > > > > in memory? We have also Support Multiple Rule and
> > > Dynamic
> > > >> Rule
> > > >> > > > > > Changing.
> > > >> > > > > > > > > But we are facing such a problem, some users’ usage
> > > >> scenarios
> > > >> > > are
> > > >> > > > > > that
> > > >> > > > > > > > they
> > > >> > > > > > > > > want to have their own pattern for each user_id,
> which
> > > >> means
> > > >> > > that
> > > >> > > > > > there
> > > >> > > > > > > > > could be thousands of patterns, which would make the
> > > >> > > performance
> > > >> > > > of
> > > >> > > > > > > > Pattern
> > > >> > > > > > > > > Matching very poor. We are also trying to solve this
> > > >> problem.
> > > >> > > > > > > > >
> > > >> > > > > > > > > The PatternProcessorManager keeps all the active
> > > >> > > PatternProcessor
> > > >> > > > > in
> > > >> > > > > > > > > memory. For scenarios that they want to have their
> own
> > > >> pattern
> > > >> > > > for
> > > >> > > > > > each
> > > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> > fine-grained
> > > >> pattern
> > > >> > > > of
> > > >> > > > > > > > > PatternProcessor to solve the performance problem of
> > the
> > > >> > > Pattern
> > > >> > > > > > > > Matching,
> > > >> > > > > > > > > for example, a pattern corresponds to a group of
> > users?
> > > >> The
> > > >> > > > > scenarios
> > > >> > > > > > > > > mentioned above need to be solved by case by case.
> > > >> > > > > > > > >
> > > >> > > > > > > > > Best,
> > > >> > > > > > > > > Nicholas Jiang
> > > >> > > > > > > > >
> > > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > > >> > > > > > > > > > Glad to see the Community's progress in Flink CEP.
> > > After
> > > >> > > > reading
> > > >> > > > > > this
> > > >> > > > > > > > > Flip,
> > > >> > > > > > > > > > I have few questions, would you please take a look
> > ?
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > > >> > > > PatternProcessoerDiscoverer
> > > >> > > > > to
> > > >> > > > > > > > > update
> > > >> > > > > > > > > > the rules, will it increase the load of JM? For
> > > >> example, if
> > > >> > > the
> > > >> > > > > > user
> > > >> > > > > > > > > wants
> > > >> > > > > > > > > > the updated rule to take effect immediately,,
> which
> > > >> means
> > > >> > > that
> > > >> > > > we
> > > >> > > > > > need
> > > >> > > > > > > > to
> > > >> > > > > > > > > > set a shorter check interval or there is another
> > > >> scenario
> > > >> > > when
> > > >> > > > > > users
> > > >> > > > > > > > > > rarely update the pattern, will the
> > > >> > > PatternProcessoerDiscoverer
> > > >> > > > > be
> > > >> > > > > > in
> > > >> > > > > > > > > most
> > > >> > > > > > > > > > of the time Do useless checks ? Will a lazy update
> > > mode
> > > >> could
> > > >> > > > be
> > > >> > > > > > used,
> > > >> > > > > > > > > > which the pattern only be updated when triggered
> by
> > > the
> > > >> user,
> > > >> > > > and
> > > >> > > > > > do
> > > >> > > > > > > > > > nothing at other times ?
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > 2. I still have some confusion about how Key
> > > >> Generating
> > > >> > > > > > Opertator and
> > > >> > > > > > > > > > CepOperator (Pattern Matching & Processing
> Operator)
> > > >> work
> > > >> > > > > > together. If
> > > >> > > > > > > > > > there are N PatternProcessors, will the Key
> > Generating
> > > >> > > > Opertator
> > > >> > > > > > > > > generate N
> > > >> > > > > > > > > > keyedStreams, and then N CepOperator would process
> > > each
> > > >> Key
> > > >> > > > > > separately
> > > >> > > > > > > > ?
> > > >> > > > > > > > > Or
> > > >> > > > > > > > > > every CepOperator Task would process all patterns,
> > if
> > > >> so,
> > > >> > > does
> > > >> > > > > the
> > > >> > > > > > key
> > > >> > > > > > > > > type
> > > >> > > > > > > > > > in each PatternProcessor need to be the same ?
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > 3. Maybe need to pay attention to it when
> > implementing
> > > >> it .If
> > > >> > > > > some
> > > >> > > > > > > > > Pattern
> > > >> > > > > > > > > > has been removed or updateed ,will the partially
> > > >> matched
> > > >> > > > results
> > > >> > > > > > in
> > > >> > > > > > > > > > StateBackend would be clean up or We rely on state
> > ttl
> > > >> to
> > > >> > > clean
> > > >> > > > > up
> > > >> > > > > > > > these
> > > >> > > > > > > > > > expired states.
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > 4. Will the PatternProcessorManager keep all the
> > > active
> > > >> > > > > > > > PatternProcessor
> > > >> > > > > > > > > in
> > > >> > > > > > > > > > memory ? We have also Support Multiple Rule and
> > > Dynamic
> > > >> Rule
> > > >> > > > > > Changing .
> > > >> > > > > > > > > > But we are facing such a problem, some users’
> usage
> > > >> scenarios
> > > >> > > > are
> > > >> > > > > > that
> > > >> > > > > > > > > they
> > > >> > > > > > > > > > want to have their own pattern for each user_id,
> > which
> > > >> means
> > > >> > > > that
> > > >> > > > > > there
> > > >> > > > > > > > > > could be thousands of patterns, which would make
> the
> > > >> > > > performance
> > > >> > > > > of
> > > >> > > > > > > > > Pattern
> > > >> > > > > > > > > > Matching very poor. We are also trying to solve
> this
> > > >> problem.
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > Yunfeng Zhou <fl...@gmail.com>
> > > >> 于2021年12月10日周五
> > > >> > > > > 19:16写道：
> > > >> > > > > > > > > >
> > > >> > > > > > > > > > > Hi all，
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > I'm opening this thread to propose the design to
> > > >> support
> > > >> > > > > multiple
> > > >> > > > > > > > rule
> > > >> > > > > > > > > &
> > > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP project,
> as
> > > >> > > described
> > > >> > > > in
> > > >> > > > > > > > > FLIP-200
> > > >> > > > > > > > > > > [1]
> > > >> > > > > > > > > > > .
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > Currently Flink CEP only supports having a
> single
> > > >> pattern
> > > >> > > > > inside
> > > >> > > > > > a
> > > >> > > > > > > > > > > CepOperator and does not support changing the
> > > pattern
> > > >> > > > > > dynamically. In
> > > >> > > > > > > > > order
> > > >> > > > > > > > > > > to reduce resource consumption and to experience
> > > >> shorter
> > > >> > > > > downtime
> > > >> > > > > > > > > during
> > > >> > > > > > > > > > > pattern updates, there is a growing need in the
> > > >> production
> > > >> > > > > > > > environment
> > > >> > > > > > > > > that
> > > >> > > > > > > > > > > expects CEP to support having multiple patterns
> in
> > > one
> > > >> > > > operator
> > > >> > > > > > and
> > > >> > > > > > > > to
> > > >> > > > > > > > > > > support dynamically changing them. Therefore I
> > > >> propose to
> > > >> > > add
> > > >> > > > > > certain
> > > >> > > > > > > > > > > infrastructure as described in FLIP-200 to
> support
> > > >> these
> > > >> > > > > > > > > functionalities.
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > Please feel free to reply to this email thread.
> > > >> Looking
> > > >> > > > forward
> > > >> > > > > > to
> > > >> > > > > > > > your
> > > >> > > > > > > > > > > feedback!
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > [1]
> > > >> > > > > > > > > > >
> > > >> > > > > > > > >
> > > >> > > > > > > >
> > > >> > > > > >
> > > >> > > > >
> > > >> > > >
> > > >> > >
> > > >>
> > >
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > Best regards,
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > > > Yunfeng
> > > >> > > > > > > > > > >
> > > >> > > > > > > > > >
> > > >> > > > > > > > >
> > > >> > > > > > > >
> > > >> > > > > > > >
> > > >> > > > > > > > --
> > > >> > > > > > > >
> > > >> > > > > > > > Konstantin Knauf
> > > >> > > > > > > >
> > > >> > > > > > > > https://twitter.com/snntrable
> > > >> > > > > > > >
> > > >> > > > > > > > https://github.com/knaufk
> > > >> > > > > > > >
> > > >> > > > > > >
> > > >> > > > > >
> > > >> > > > >
> > > >> > > >
> > > >> > >
> > > >> > >
> > > >> > > --
> > > >> > >
> > > >> > > Konstantin Knauf
> > > >> > >
> > > >> > > https://twitter.com/snntrable
> > > >> > >
> > > >> > > https://github.com/knaufk
> > > >> > >
> > > >> >
> > > >>
> > > >
> > >
> >
>
Re: [DISCUSS] FLIP-200: Support Multiple Rule and Dynamic Rule Changing (Flink CEP)
Posted by Till Rohrmann <tr...@apache.org>.
Hi Becket,
Thanks for the explanation. While I do agree that a general 2-way
communication pattern would be nice to have, I also believe that this
approach is probably at least one magnitude more complex to realize than
the side-input approach. Therefore, I really would like to understand why
such a mechanism is required for the CEP use case.
You mentioned that a TM might find out that a pattern is invalid and then
it could use the 2-way communication with the JM to tell the other TMs that
the pattern is invalid. How exactly would a TM detect that a pattern is
invalid at data processing time? And assuming that this is possible for a
single TM, why can't the other TMs not detect this problem? Is it because
the validity of patterns might depend on data that is different between TMs?
You also mentioned that deep-learning-on-flink could benefit from an OC
control plane but I couldn't find the referenced link. Would
deep-learning-on-flink like to use OCs as a kind of parameter server? Could
you elaborate on deep-learning-on-flink's usage of such a feature?
Concerning reprocessing command history and repeatable processing results I
think there is actually quite a big difference between using a Flink source
vs. offering a REST server that can receive command that are distributed
via the OCs. In the former case we can rely on the external system to
persist commands whereas in the latter approach we/users have to implement
a storage solution on their own (in the simplest case users will probably
store everything in state which might grow indefinitely if stored as a
changelog).
Cheers,
Till
On Tue, Jan 4, 2022 at 6:41 AM Becket Qin <be...@gmail.com> wrote:
> Hi David,
>
> Thanks for sharing your thoughts. Some quick reply to your comments:
>
> We're still talking about the "web server based"
> > pattern_processor_discoverer, but what about other use cases? One of my
> big
> > concerns is that user's can not really reuse any part of the Flink
> > ecosystem to implement the discovery logic. For example if they want to
> > read patterns from Kafka topic, they need to roll their own discoverer
> > based on the vanilla Kafka client. If we're talking about extensibility,
> > should we also make sure that the existing primitives can be reused?
>
>
> KafkaSource is actually more complicated than vanilla KafkaConsumer from
> the perspective of consuming Kafka messages. The KafkaSource just helps
> make it easier for Flink jobs to process these messages. In fact,
> KafkaConsumer is more powerful than KafkaSource in terms of talking to
> Kafka. So we are comparing [KafkaConsumer + OperatorCoordinator] and
> [KafkaSource + side-input], not [KafkaConsumer + side-input].
>
> This can be done for the side-input as well by filtering invalid patterns
> > before the broadcast. You can also send the invalid patterns to any side
> > output you want. I have a feeling that we're way too attached to the REST
> > server use case in this discussion. I agree that for that case, this
> > solution is the most straightforward one.
>
>
> Depending on whether the invalidity is discovered in pattern definition
> time or data processing time. e.g. A valid pattern with invalid data which
> fails to process can only be detected in data processing time. So the
> pattern won't be filtered out before the broadcast.
>
> I agree that 2-way communication in the "data-flow like" API is tricky,
> > because it requires cycles / iterations, which are still not really
> solved
> > (for a good reason, it's really tough nut to crack). This makes me think
> > that the OC may be bit of a "incomplete" workaround for not having fully
> > working support for iterations.
>
>
> For example I'm not really confident that the checkpointing of the OC works
> > correctly right now, because it doesn't seem to require checkpoint
> barrier
> > alignment as the regular stream inputs. We also don't have a proper
> support
> > for watermarking (this is again tricky, because of the cycle).
>
>
> If we decide to go down this road, should we first address some of these
> > limitations?
>
> I agree. OC is proven to be useful and we should think about how to enhance
> it instead of not using it.
>
> If I understand that correctly, this means only the LATEST state of the
> > patterns (in other words - patterns that are currently in use). Is this
> > really sufficient for historical re-processing? Can someone for example
> > want re-process the data in more of a "temporal join" fashion? Also AFAIK
> > historical processing in combination with "coordinator checkpoints" is
> not
> > really something that we currently support of the box, are there any
> plans
> > on tackling this (my other concern is that this should not go against the
> > "unified batch & stream processing" efforts)?
>
> I think in this case, the state would contain the entire pattern update
> history. Not the final state, but the change log. In fact, it is not
> possible to guarantee the correct result unless you have the entire change
> log. Even with side-input, there still could be late arrivals in the
> pattern update stream, and the only way to correct it is to either have all
> the data reprocessed (with all the pattern change log loaded upfront) or
> having retraction support.
>
> I can imagine that if this should be a concern, we could move the execution
> > of the OC to the task managers. This also makes me thing, that we
> shouldn't
> > make any strong assumptions that the OC will always run in the JobManager
> > (this is especially relevant for the embedded web-server use case).
>
> This is a very good point. I think we should do this. The reason OC is in
> JM is based on the assumption that control plane usually have little
> traffic. But if that is not the case, we should move the OC out of JM,
> maybe to TM.
>
>
>
> I think the key topic we are discussing is what the Flink control plane
> should look like, and CEP is just an example use case. There are basically
> two options:
>
> 1. Using the side-input / broadcast stream
> 2. Using the OperatorCoordinator.
>
> Although we are having this discussion under the context of supporting CEP
> dynamic pattern update, it would be really helpful to reach agreement on
> the design principle in general of how Flink should handle similar external
> control demands, a.k.a how to provide a decent control plane in Flink to
> the users.
>
> Here is my take on these two options, based on the requirements of a
> control plane.
>
> *Communication Requirements*
> Flink has two kinds of control planes - in-band and out-of-band.
> In-band control plane is like watermark and checkpoint marker. It requires
> the entire DAG to be in a consistent state, so the control messages flow
> with the data in one direction. This is a one-way control flow.
> Examples of out-of-band control plane is OC and JM/TM communication. They
> do not require a global consistency or awareness across the entire DAG.
>
> Before OC, neither of these two kinds of control plain was exposed to the
> users. OC allows the users to leverage the out-of-band control plane so
> they can coordinate across subtasks. This is a more widely used control
> flow from user defined operator perspective which requires 2-way
> communication.
>
> - side-input stream is one-way communication. Moreover, I don't think
> iteration is the right way to address this. Unlike the abstraction of
> data
> processing which is a DAG, the control plane may require communication
> between arbitrary two operators in different orders. Using iterations
> may
> end up with an explosion of feedback edges that are not only
> complicated to
> express, but also hard to debug and maintain.
> - OC provides a decent 2-way communication mechanism.
>
>
> *Cost for low traffic use case*
> An important difference between data channel and control channel is traffic
> pattern. Unlike data plane, the control plane is usually idle for the vast
> majority of the time with occasional control messages.
>
> - One argument to use the side-input / broadcast stream was that users
> can reuse the existing connectors. However, most Flink sources are
> designed
> to handle large throughput of traffic that maintains all the threads,
> network connections, etc. Not to say the external resources such as
> Kafka
> topics to store the commands.
> - OC can have a much lower constant cost.
>
>
> *Easy to use*
> Personally speaking, I think the most simple and user-friendly interface is
> a REST API that accepts control commands.
>
> - One proposal at this point is to have a separate web server
> independent of the Flink job. In that case, should users implement that
> web
> server? In order to pass the command to the Flink job, does that mean
> users
> should implement a Flink source that can read the commands from the web
> server? Or the web server would send the command to something like Kafka
> and let the Flink side-input read from there. There seems to be a lot
> for
> the users to do. And it seems an unnecessarily complicated system to
> build
> to send occasional control messages to a Flink job.
> - OC can simply be reached via the JM REST API.
> - e.g. http://JM_IP/OperatorEvents?OP_NAME=xxx&Content=xxx
> <http://jm_ip/OperatorEvents?OP_NAME=xxx&Content=xxx> would simply
> send the Content to the OC of OP_NAME.
>
> *Work well with checkpoints*
>
> - side-input streams works well with checkpoint, thanks to its
> compatibility to the DAG abstraction.
> - The OperatorCoordinator requires more careful design to work well with
> checkpoints. The complexity mostly comes from the 2-way communication.
> At
> this point the OperatorCoordinator message delivery semantic may not be
> as
> robust as side-input streams. However, I think this is mainly due to
> potential bugs in implementation instead of fundamental design problems.
> Basically the checkpoint semantic should be:
> - The JM will first checkpoint all the OperatorCoordinator, more
> specifically for each OperatorCoordinator,
> - 1) JM blocks the input queue to stop receiving new events from
> the subtasks.
> - 2) let all the operator coordinator finish processing all the
> pending events in the OC input queue.
> - 3) flush the OC output queue until all the events sent are
> acknowledged.
> - 3) unblock the input queue, but block the output queue until all
> the subtasks of the OC finish checkpoints.
> - The JM starts a normal checkpoint starting from the Source.
> - If an operator has a coordinator, and it has sent some events to
> the OC but has not been acknowledged. These events need to be
> put into the
> subtasks' checkpoint.
> - After all the subtasks of an operator finishes checkpoint, the
> output queue of the corresponding OC can be unblocked.
> It looks that the above protocol would let OC have a clear checkpoint
> semantic. And this complexity seems must for 2-way communication. I
> think
> we are able to hide the above protocol from users by having an abstract
> OC
> implementation.
>
>
> *Reprocess command history and repeatable processing results*
> This seems not something generally required for a control plane. But if the
> control plane changes the data processing behavior, there might be some use
> case. Just like the CEP pattern update. In order to do this, users will
> need to provide a full command history to the operators. That consists of
> two steps:
>
> 1. get the full command history. (Flink Source V.S. Custom way to
> retrieve command history.)
> 2. send them to the operators. (Side-input V.S. OC/Operator
> communication)l
>
> I actually don't feel much difference between these two options. I am not
> sure if a Flink source is necessarily simpler than the user implemented
> logic. For example, if all the changes are just written in a database
> table. From the user's perspective, I feel fine with querying the DB by
> myself using something like JDBC (or use KafkaConsumer to read the pattern
> history from a Kafka topic) and send all the pattern change history to the
> operators before they start to process the actual events.
>
> *Stability impact to the Flink Job*
> I agree this is a valid concern. There is only one JM and currently OC runs
> there, which may potentially cause JM crash and result in job failure.
> Running in TM may have a less impact. So I think it makes sense to run OC
> in TM. However, this is more of how we can implement OC to make it more
> robust. It does not forfeit the other semantic and user experience benefits
> mentioned above.
>
>
> To sum up:
> 1. Regardless of whether CEP chooses OC or side-input stream, a decent
> 2-way communication control plane seems really helpful and has been proven
> by quite a few existing use cases. To me the question is how to make it
> more robust, not whether we should use it or not.
> 2. As for CEP, if we assume OC will be robust enough, personally I feel OC
> is a better fit than side-input mainly because of the simplicity and
> extensibility.
>
> Thanks,
>
> Jiangjie (Becket) Qin
>
>
> On Thu, Dec 30, 2021 at 8:43 PM David Morávek <dm...@apache.org> wrote:
>
> > Hi all,
> >
> > sorry for the late reply, vacation season ;) I'm still not 100% sold on
> > choosing the OC for this use-case, but on the other hand I don't have
> > strong arguments against it. Few more questions / thoughts:
> >
> > We're still talking about the "web server based"
> > pattern_processor_discoverer, but what about other use cases? One of my
> big
> > concerns is that user's can not really reuse any part of the Flink
> > ecosystem to implement the discovery logic. For example if they want to
> > read patterns from Kafka topic, they need to roll their own discoverer
> > based on the vanilla Kafka client. If we're talking about extensibility,
> > should we also make sure that the existing primitives can be reused?
> >
> > For instance, the example I gave in my previous email seems not easily
> > > achievable with side-input / broadcast streams: a single invalid
> pattern
> > > detected on a TM can be disabled elegantly globally without crashing
> the
> > > entire Flink job.
> >
> >
> > This can be done for the side-input as well by filtering invalid patterns
> > before the broadcast. You can also send the invalid patterns to any side
> > output you want. I have a feeling that we're way too attached to the REST
> > server use case in this discussion. I agree that for that case, this
> > solution is the most straightforward one.
> >
> > OC is a 2-way communication mechanism, i.e. a subtask can also send
> > > OperatorEvent to the coordinator to report its owns status, so that the
> > > coordinator can act accordingly.
> > >
> >
> > I agree that 2-way communication in the "data-flow like" API is tricky,
> > because it requires cycles / iterations, which are still not really
> solved
> > (for a good reason, it's really tough nut to crack). This makes me think
> > that the OC may be bit of a "incomplete" workaround for not having fully
> > working support for iterations.
> >
> > For example I'm not really confident that the checkpointing of the OC
> works
> > correctly right now, because it doesn't seem to require checkpoint
> barrier
> > alignment as the regular stream inputs. We also don't have a proper
> support
> > for watermarking (this is again tricky, because of the cycle).
> >
> > If we decide to go down this road, should we first address some of these
> > limitations?
> >
> > OperatorCoordinator will checkpoint the full amount of PatternProcessor
> > > data. For the reprocessing of historical data, you can read the
> > > PatternProcessor snapshots saved by this checkpoint from a certain
> > > historical checkpoint, and then recreate the historical data through
> > these
> > > PatternProcessor snapshots.
> > >
> >
> > If I understand that correctly, this means only the LATEST state of the
> > patterns (in other words - patterns that are currently in use). Is this
> > really sufficient for historical re-processing? Can someone for example
> > want re-process the data in more of a "temporal join" fashion? Also AFAIK
> > historical processing in combination with "coordinator checkpoints" is
> not
> > really something that we currently support of the box, are there any
> plans
> > on tackling this (my other concern is that this should not go against the
> > "unified batch & stream processing" efforts)?
> >
> > I do agree that having the user defined control logic defined in the JM
> > > increases the chance of instability.
> > >
> >
> > I can imagine that if this should be a concern, we could move the
> execution
> > of the OC to the task managers. This also makes me thing, that we
> shouldn't
> > make any strong assumptions that the OC will always run in the JobManager
> > (this is especially relevant for the embedded web-server use case).
> >
> > If an agreement is reached on OperatorCoodinator, I will start the voting
> > > thread.
> > >
> >
> > As for the vote, I'd would be great if we can wait until the next week as
> > many people took vacation until end of the year.
> >
> > Overall, I really like the feature, this will be a great addition to
> Flink.
> >
> > Best,
> > D.
> >
> >
> >
> > On Thu, Dec 30, 2021 at 11:27 AM Martijn Visser <ma...@ververica.com>
> > wrote:
> >
> > > Hi all,
> > >
> > > I can understand the need for a control plane mechanism. I'm not the
> > > technical go-to person for questions on the OperatorCoordinator, but I
> > > would expect that we could offer those interfaces from Flink but
> > shouldn't
> > > recommend running user-code in the JobManager itself. I think the user
> > code
> > > (like a webserver) should run outside of Flink (like via a sidecar) and
> > use
> > > only the provided interfaces to communicate.
> > >
> > > I would like to get @David Morávek <dm...@apache.org> opinion on the
> > > technical part.
> > >
> > > Best regards,
> > >
> > > Martijn
> > >
> > > On Thu, 30 Dec 2021 at 10:07, Nicholas Jiang <nicholasjiang@apache.org
> >
> > > wrote:
> > >
> > >> Hi Konstantin, Becket, Martijn,
> > >>
> > >> Thanks for sharing your feedback. What other concerns do you have
> about
> > >> OperatorCoodinator? If an agreement is reached on OperatorCoodinator,
> I
> > >> will start the voting thread.
> > >>
> > >> Best,
> > >> Nicholas Jiang
> > >>
> > >> On 2021/12/22 03:19:58 Becket Qin wrote:
> > >> > Hi Konstantin,
> > >> >
> > >> > Thanks for sharing your thoughts. Please see the reply inline below.
> > >> >
> > >> > Thanks,
> > >> >
> > >> > Jiangjie (Becket) Qin
> > >> >
> > >> > On Tue, Dec 21, 2021 at 7:14 PM Konstantin Knauf <knaufk@apache.org
> >
> > >> wrote:
> > >> >
> > >> > > Hi Becket, Hi Nicholas,
> > >> > >
> > >> > > Thanks for joining the discussion.
> > >> > >
> > >> > > 1 ) Personally, I would argue that we should only run user code in
> > the
> > >> > > Jobmanager/Jobmaster if we can not avoid it. It seems wrong to me
> to
> > >> > > encourage users to e.g. run a webserver on the Jobmanager, or
> > >> continuously
> > >> > > read patterns from a Kafka Topic on the Jobmanager, but both of
> > these
> > >> I see
> > >> > > happening with the current design. We've had lots of issues with
> > >> > > classloading leaks and other stability issues on the Jobmanager
> and
> > >> making
> > >> > > this more complicated, if there is another way, seems unnecessary.
> > >> >
> > >> >
> > >> > I think the key question here is what primitive does Flink provide
> to
> > >> > facilitate the user implementation of their own control logic /
> > control
> > >> > plane? It looks that previously, Flink assumes that all the user
> logic
> > >> is
> > >> > just data processing logic without any control / coordination
> > >> requirements.
> > >> > However, it turns out that a decent control plane abstraction is
> > >> required
> > >> > in association with the data processing logic in many cases,
> including
> > >> > Source / Sink and other user defined operators in general. The fact
> > >> that we
> > >> > ended up with adding the SplitEnumerator and GlobalCommitter are
> just
> > >> two
> > >> > examples of the demand of such coordination among user defined
> logics.
> > >> > There are other cases that we see in ecosystem projects, such as
> > >> > deep-learning-on-flink[1]. Now we see this again in CEP.
> > >> >
> > >> > Such control plane primitives are critical to the extensibility of a
> > >> > project. If we look at other projects, exposing such control plane
> > >> logic is
> > >> > quite common. For example, Hadoop ended up with exposing YARN as a
> > >> public
> > >> > API to the users, which is extremely popular. Kafka consumers
> exposed
> > >> the
> > >> > consumer group rebalance logic to the users via
> > >> ConsumerPartitionAssigner,
> > >> > which is also a control plane primitive.
> > >> >
> > >> > To me it is more important to think about how we can improve the
> > >> stability
> > >> > of such a control plane mechanism, instead of simply saying no to
> the
> > >> users.
> > >> >
> > >> >
> > >> >
> > >> >
> > >> > > 2) In addition, I suspect that, over time we will have to
> implement
> > >> all the
> > >> > > functionality that regular sources already provide around
> > consistency
> > >> > > (watermarks, checkpointing) for the PatternProcessorCoordinator,
> > too.
> > >> >
> > >> >
> > >> > I think OperatorCoordinator should have a generic communication
> > >> mechanism
> > >> > for all the operators, not specific to Source. We should probably
> have
> > >> an
> > >> > AbstractOperatorCoordinator help dealing with the communication
> layer,
> > >> and
> > >> > leave the state maintenance and event handling logic to the user
> code.
> > >> >
> > >> >
> > >> > > 3) I understand that running on the Jobmanager is easier if you
> want
> > >> to
> > >> > > launch a REST server directly. Here my question would be: does
> this
> > >> really
> > >> > > need to be solved inside of Flink or couldn't you start a
> webserver
> > >> next to
> > >> > > Flink? If we start using the Jobmanager as a REST server users
> will
> > >> expect
> > >> > > that e.g. it is highly available and can be load balanced and we
> > >> quickly
> > >> > > need to think about aspects that we never wanted to think about in
> > the
> > >> > > context of a Flink Jobmanager.
> > >> > >
> > >> >
> > >> > I think the REST API is just for receiving commands targeting a
> > running
> > >> > Flink job. If the job fails, the REST API would be useless.
> > >> >
> > >> >
> > >> > > So, can you elaborate a bit more, why a side-input/broadcast
> stream
> > is
> > >> > >
> > >> > > a) more difficult
> > >> > > b) has vague semantics (To me semantics of a stream-stream seem
> > >> clearer
> > >> > > when it comes to out-of-orderness, late data, reprocessing or
> batch
> > >> > > execution mode.)
> > >> >
> > >> >
> > >> > I do agree that having the user defined control logic defined in the
> > JM
> > >> > increases the chance of instability. In that case, we may think of
> > other
> > >> > solutions and I am fully open to that. But the side-input /
> broadcast
> > >> > stream seems more like a bandaid instead of a carefully designed
> > control
> > >> > plane mechanism.
> > >> >
> > >> > A decent control plane requires two-way communication, so
> information
> > >> can
> > >> > be reported / collected from the entity being controlled, and the
> > >> > coordinator / controller can send decisions or commands to the
> > entities
> > >> > accordingly, just like our TM / JM communication. IIUC, this is not
> > >> > achievable with the existing side-input / broadcast stream as both
> of
> > >> them
> > >> > are one-way communication mechanisms. For instance, the example I
> gave
> > >> in
> > >> > my previous email seems not easily achievable with side-input /
> > >> broadcast
> > >> > streams: a single invalid pattern detected on a TM can be disabled
> > >> > elegantly globally without crashing the entire Flink job.
> > >> >
> > >> >
> > >> > > Cheers,
> > >> > >
> > >> > > Konstantin
> > >> > >
> > >> > >
> > >> > > On Tue, Dec 21, 2021 at 11:38 AM Becket Qin <becket.qin@gmail.com
> >
> > >> wrote:
> > >> > >
> > >> > > > Hi folks,
> > >> > > >
> > >> > > > I just finished reading the previous emails. It was a good
> > >> discussion.
> > >> > > Here
> > >> > > > are my two cents:
> > >> > > >
> > >> > > > *Is OperatorCoordinator a public API?*
> > >> > > > Regarding the OperatorCoordinator, although it is marked as
> > internal
> > >> > > > interface at this point, I intended to make it a public
> interface
> > >> when
> > >> > > add
> > >> > > > that in FLIP-27. This is a powerful cross-subtask communication
> > >> mechanism
> > >> > > > that enables many use cases, Source / Sink / TF on Flink / CEP
> > here
> > >> > > again.
> > >> > > > To my understanding, OC was marked as internal because we think
> it
> > >> is not
> > >> > > > stable enough yet. We may need to fortify the OperatorEvent
> > delivery
> > >> > > > semantic a little bit so it works well with checkpoint in
> general.
> > >> > > >
> > >> > > > I think it is a valid concern that user code running in JM may
> > cause
> > >> > > > instability. However, not providing this communication mechanism
> > >> only
> > >> > > makes
> > >> > > > a lot of use case even harder to implement. So it seems that
> > having
> > >> the
> > >> > > OC
> > >> > > > exposed to end users brings more benefits than harm to Flink. At
> > >> the end
> > >> > > of
> > >> > > > the day, users have many ways to crash a Flink job if they do
> not
> > >> write
> > >> > > > proper code. So making those who know what they do happy seems
> > more
> > >> > > > important here.
> > >> > > >
> > >> > > > *OperatorCoordinator V.S. side-input / broadcast stream*
> > >> > > > I think both of them can achieve the goal of dynamic patterns.
> The
> > >> main
> > >> > > > difference is the extensibility.
> > >> > > >
> > >> > > > OC is a 2-way communication mechanism, i.e. a subtask can also
> > send
> > >> > > > OperatorEvent to the coordinator to report its owns status, so
> > that
> > >> the
> > >> > > > coordinator can act accordingly. This is sometimes useful. For
> > >> example, a
> > >> > > > single invalid pattern can be disabled elegantly without
> crashing
> > >> the
> > >> > > > entire Flink job. In the future, if we allow users to send
> > external
> > >> > > command
> > >> > > > to OC via JM, a default self-contained implementation can just
> > >> update the
> > >> > > > pattern via the REST API without external dependencies.
> > >> > > >
> > >> > > > Another reason I personally prefer OC is because it is an
> explicit
> > >> > > control
> > >> > > > plain mechanism, where as the side-input / broadcast stream has
> > are
> > >> more
> > >> > > > vague semantic.
> > >> > > >
> > >> > > > Thanks,
> > >> > > >
> > >> > > > Jiangjie (Becket) Qin
> > >> > > >
> > >> > > > On Tue, Dec 21, 2021 at 4:25 PM David Morávek <dm...@apache.org>
> > >> wrote:
> > >> > > >
> > >> > > > > Hi Yunfeng,
> > >> > > > >
> > >> > > > > thanks for drafting this FLIP, this will be a great addition
> > into
> > >> the
> > >> > > CEP
> > >> > > > > toolbox!
> > >> > > > >
> > >> > > > > Apart from running user code in JM, which want to avoid in
> > >> general, I'd
> > >> > > > > have one more another concern about using the
> > OperatorCoordinator
> > >> and
> > >> > > > that
> > >> > > > > is re-processing of the historical data. Any thoughts about
> how
> > >> this
> > >> > > will
> > >> > > > > work with the OC?
> > >> > > > >
> > >> > > > > I have a slight feeling that a side-input (custom source /
> > >> operator +
> > >> > > > > broadcast) would a better fit for this case. This would
> simplify
> > >> the
> > >> > > > > consistency concerns (watermarks + pushback) and the
> > >> re-processing of
> > >> > > > > historical data.
> > >> > > > >
> > >> > > > > Best,
> > >> > > > > D.
> > >> > > > >
> > >> > > > >
> > >> > > > > On Tue, Dec 21, 2021 at 6:47 AM Nicholas Jiang <
> > >> > > nicholasjiang@apache.org
> > >> > > > >
> > >> > > > > wrote:
> > >> > > > >
> > >> > > > > > Hi Konstantin, Martijn
> > >> > > > > >
> > >> > > > > > Thanks for the detailed feedback in the discussion. What I
> > >> still have
> > >> > > > > left
> > >> > > > > > to answer/reply to:
> > >> > > > > >
> > >> > > > > > -- Martijn: Just to be sure, this indeed would mean that if
> > for
> > >> > > > whatever
> > >> > > > > > reason the heartbeat timeout, it would crash the job, right?
> > >> > > > > >
> > >> > > > > > IMO, if for whatever reason the heartbeat timeout, it
> couldn't
> > >> check
> > >> > > > the
> > >> > > > > > PatternProcessor consistency between the OperatorCoordinator
> > >> and the
> > >> > > > > > subtasks so that the job would be crashed.
> > >> > > > > >
> > >> > > > > > -- Konstantin: What I was concerned about is that we
> basically
> > >> let
> > >> > > > users
> > >> > > > > > run a UserFunction in the OperatorCoordinator, which it does
> > >> not seem
> > >> > > > to
> > >> > > > > > have been designed for.
> > >> > > > > >
> > >> > > > > > In general, we have reached an agreement on the design of
> this
> > >> FLIP,
> > >> > > > but
> > >> > > > > > there are some concerns on the OperatorCoordinator, about
> > >> whether
> > >> > > > > basically
> > >> > > > > > let users run a UserFunction in the OperatorCoordinator is
> > >> designed
> > >> > > for
> > >> > > > > > OperatorCoordinator. We would like to invite Becket Qin who
> is
> > >> the
> > >> > > > author
> > >> > > > > > of OperatorCoordinator to help us to answer this concern.
> > >> > > > > >
> > >> > > > > > Best,
> > >> > > > > > Nicholas Jiang
> > >> > > > > >
> > >> > > > > >
> > >> > > > > > On 2021/12/20 10:07:14 Martijn Visser wrote:
> > >> > > > > > > Hi all,
> > >> > > > > > >
> > >> > > > > > > Really like the discussion on this topic moving forward. I
> > >> really
> > >> > > > think
> > >> > > > > > > this feature will be much appreciated by the Flink users.
> > >> What I
> > >> > > > still
> > >> > > > > > have
> > >> > > > > > > left to answer/reply to:
> > >> > > > > > >
> > >> > > > > > > -- Good point. If for whatever reason the different
> > >> taskmanagers
> > >> > > > can't
> > >> > > > > > get
> > >> > > > > > > the latest rule, the Operator Coordinator could send a
> > >> heartbeat to
> > >> > > > all
> > >> > > > > > > taskmanagers with the latest rules and check the heartbeat
> > >> response
> > >> > > > > from
> > >> > > > > > > all the taskmanagers whether the latest rules of the
> > >> taskmanager is
> > >> > > > > equal
> > >> > > > > > > to these of the Operator Coordinator.
> > >> > > > > > >
> > >> > > > > > > Just to be sure, this indeed would mean that if for
> whatever
> > >> reason
> > >> > > > the
> > >> > > > > > > heartbeat timeout, it would crash the job, right?
> > >> > > > > > >
> > >> > > > > > > -- We have consided about the solution mentioned above. In
> > >> this
> > >> > > > > > solution, I
> > >> > > > > > > have some questions about how to guarantee the consistency
> > of
> > >> the
> > >> > > > rule
> > >> > > > > > > between each TaskManager. By having a coodinator in the
> > >> JobManager
> > >> > > to
> > >> > > > > > > centrally manage the latest rules, the latest rules of all
> > >> > > > TaskManagers
> > >> > > > > > are
> > >> > > > > > > consistent with those of the JobManager, so as to avoid
> the
> > >> > > > > > inconsistencies
> > >> > > > > > > that may be encountered in the above solution. Can you
> > >> introduce
> > >> > > how
> > >> > > > > this
> > >> > > > > > > solution guarantees the consistency of the rules?
> > >> > > > > > >
> > >> > > > > > > The consistency that we could guarantee was based on how
> > >> often each
> > >> > > > > > > TaskManager would do a refresh and how often we would
> > accept a
> > >> > > > refresh
> > >> > > > > to
> > >> > > > > > > fail. We set the refresh time to a relatively short one
> (30
> > >> > > seconds)
> > >> > > > > and
> > >> > > > > > > maximum failures to 3. That meant that we could guarantee
> > that
> > >> > > rules
> > >> > > > > > would
> > >> > > > > > > be updated in < 2 minutes or else the job would crash.
> That
> > >> was
> > >> > > > > > sufficient
> > >> > > > > > > for our use cases. This also really depends on how big
> your
> > >> cluster
> > >> > > > > is. I
> > >> > > > > > > can imagine that if you have a large scale cluster that
> you
> > >> want to
> > >> > > > > run,
> > >> > > > > > > you don't want to DDOS the backend system where you have
> > your
> > >> rules
> > >> > > > > > stored.
> > >> > > > > > >
> > >> > > > > > > -- In summary, the current design is that JobManager tells
> > all
> > >> > > > > > TaskManagers
> > >> > > > > > > the latest rules through OperatorCoodinator, and will
> > >> initiate a
> > >> > > > > > heartbeat
> > >> > > > > > > to check whether the latest rules on each TaskManager are
> > >> > > consistent.
> > >> > > > > We
> > >> > > > > > > will describe how to deal with the Failover scenario in
> more
> > >> detail
> > >> > > > on
> > >> > > > > > FLIP.
> > >> > > > > > >
> > >> > > > > > > Thanks for that. I think having the JobManager tell the
> > >> > > TaskManagers
> > >> > > > > the
> > >> > > > > > > applicable rules would indeed end up being the best
> design.
> > >> > > > > > >
> > >> > > > > > > -- about the concerns around consistency raised by
> Martijn:
> > I
> > >> > > think a
> > >> > > > > lot
> > >> > > > > > > of those can be mitigated by using an event time timestamp
> > >> from
> > >> > > which
> > >> > > > > the
> > >> > > > > > > rules take effect. The reprocessing scenario, for example,
> > is
> > >> > > covered
> > >> > > > > by
> > >> > > > > > > this. If a pattern processor should become active as soon
> as
> > >> > > > possible,
> > >> > > > > > > there will still be inconsistencies between Taskmanagers,
> > but
> > >> "as
> > >> > > > soon
> > >> > > > > as
> > >> > > > > > > possible" is vague anyway, which is why I think that's ok.
> > >> > > > > > >
> > >> > > > > > > I think an event timestamp is indeed a really important
> one.
> > >> We
> > >> > > also
> > >> > > > > used
> > >> > > > > > > that in my previous role, with the ruleActivationTimestamp
> > >> compared
> > >> > > > to
> > >> > > > > > > eventtime (well, actually we used Kafka logAppend time
> > because
> > >> > > > > > > eventtime wasn't always properly set so we used that time
> to
> > >> > > > overwrite
> > >> > > > > > the
> > >> > > > > > > eventtime from the event itself).
> > >> > > > > > >
> > >> > > > > > > Best regards,
> > >> > > > > > >
> > >> > > > > > > Martijn
> > >> > > > > > >
> > >> > > > > > > On Mon, 20 Dec 2021 at 09:08, Konstantin Knauf <
> > >> knaufk@apache.org>
> > >> > > > > > wrote:
> > >> > > > > > >
> > >> > > > > > > > Hi Nicholas, Hi Junfeng,
> > >> > > > > > > >
> > >> > > > > > > > about the concerns around consistency raised by
> Martijn: I
> > >> think
> > >> > > a
> > >> > > > > lot
> > >> > > > > > of
> > >> > > > > > > > those can be mitigated by using an event time timestamp
> > from
> > >> > > which
> > >> > > > > the
> > >> > > > > > > > rules take effect. The reprocessing scenario, for
> example,
> > >> is
> > >> > > > covered
> > >> > > > > > by
> > >> > > > > > > > this. If a pattern processor should become active as
> soon
> > as
> > >> > > > > possible,
> > >> > > > > > > > there will still be inconsistencies between
> Taskmanagers,
> > >> but "as
> > >> > > > > soon
> > >> > > > > > as
> > >> > > > > > > > possible" is vague anyway, which is why I think that's
> ok.
> > >> > > > > > > >
> > >> > > > > > > > about naming: The naming with "PatternProcessor" sounds
> > >> good to
> > >> > > me.
> > >> > > > > > Final
> > >> > > > > > > > nit: I would go for CEP#patternProccessors, which would
> be
> > >> > > > consistent
> > >> > > > > > with
> > >> > > > > > > > CEP#pattern.
> > >> > > > > > > >
> > >> > > > > > > > I am not sure about one of the rejected alternatives:
> > >> > > > > > > >
> > >> > > > > > > > > Have each subtask of an operator make the update on
> > their
> > >> own
> > >> > > > > > > >
> > >> > > > > > > > -
> > >> > > > > > > >
> > >> > > > > > > > It is hard to achieve consistency.
> > >> > > > > > > > -
> > >> > > > > > > >
> > >> > > > > > > > Though the time interval that each subtask makes
> the
> > >> update
> > >> > > > can
> > >> > > > > > be
> > >> > > > > > > > the same, the absolute time they make the update
> > >> might be
> > >> > > > > > different.
> > >> > > > > > > > For
> > >> > > > > > > > example, one makes updates at 10:00, 10:05, etc,
> > while
> > >> > > > another
> > >> > > > > > does
> > >> > > > > > > > it at
> > >> > > > > > > > 10:01, 10:06. In this case the subtasks might
> never
> > >> > > > processing
> > >> > > > > > data
> > >> > > > > > > > with
> > >> > > > > > > > the same set of pattern processors.
> > >> > > > > > > >
> > >> > > > > > > >
> > >> > > > > > > > I would have thought that it is quite easy to poll for
> the
> > >> rules
> > >> > > > from
> > >> > > > > > each
> > >> > > > > > > > Subtask at *about *the same time. So, this alone does
> not
> > >> seem to
> > >> > > > be
> > >> > > > > > > > enough to rule out this option. I've looped in David
> > >> Moravek to
> > >> > > get
> > >> > > > > his
> > >> > > > > > > > opinion of the additional load imposed on the JM.
> > >> > > > > > > >
> > >> > > > > > > > Thanks,
> > >> > > > > > > >
> > >> > > > > > > > Konstantin
> > >> > > > > > > >
> > >> > > > > > > > On Mon, Dec 20, 2021 at 4:06 AM Nicholas Jiang <
> > >> > > > > > nicholasjiang@apache.org>
> > >> > > > > > > > wrote:
> > >> > > > > > > >
> > >> > > > > > > > > Hi Yue,
> > >> > > > > > > > >
> > >> > > > > > > > > Thanks for your feedback of the FLIP. I have addressed
> > >> your
> > >> > > > > > questions and
> > >> > > > > > > > > made a corresponding explanation as follows:
> > >> > > > > > > > >
> > >> > > > > > > > > -- About Pattern Updating. If we use
> > >> > > PatternProcessoerDiscoverer
> > >> > > > to
> > >> > > > > > > > update
> > >> > > > > > > > > the rules, will it increase the load of JM? For
> example,
> > >> if the
> > >> > > > > user
> > >> > > > > > > > wants
> > >> > > > > > > > > the updated rule to take effect immediately,, which
> > means
> > >> that
> > >> > > we
> > >> > > > > > need to
> > >> > > > > > > > > set a shorter check interval or there is another
> > scenario
> > >> when
> > >> > > > > users
> > >> > > > > > > > rarely
> > >> > > > > > > > > update the pattern, will the
> PatternProcessoerDiscoverer
> > >> be in
> > >> > > > most
> > >> > > > > > of
> > >> > > > > > > > the
> > >> > > > > > > > > time Do useless checks ? Will a lazy update mode could
> > be
> > >> used,
> > >> > > > > > which the
> > >> > > > > > > > > pattern only be updated when triggered by the user,
> and
> > do
> > >> > > > nothing
> > >> > > > > at
> > >> > > > > > > > other
> > >> > > > > > > > > times?
> > >> > > > > > > > >
> > >> > > > > > > > > PatternProcessoerDiscoverer is a user-defined
> interface
> > to
> > >> > > > discover
> > >> > > > > > the
> > >> > > > > > > > > PatternProcessor updates. Periodically checking the
> > >> > > > > PatternProcessor
> > >> > > > > > in
> > >> > > > > > > > the
> > >> > > > > > > > > database is a implementation of the
> > >> PatternProcessoerDiscoverer
> > >> > > > > > > > interface,
> > >> > > > > > > > > which is that periodically querys all the
> > PatternProcessor
> > >> > > table
> > >> > > > in
> > >> > > > > > > > certain
> > >> > > > > > > > > interval. This implementation indeeds has the useless
> > >> checks,
> > >> > > and
> > >> > > > > > could
> > >> > > > > > > > > directly integrates the changelog of the table. In
> > >> addition, in
> > >> > > > > > addition
> > >> > > > > > > > to
> > >> > > > > > > > > the implementation of periodically checking the
> > database,
> > >> there
> > >> > > > are
> > >> > > > > > other
> > >> > > > > > > > > implementations such as the PatternProcessor that
> > provides
> > >> > > > Restful
> > >> > > > > > > > services
> > >> > > > > > > > > to receive updates.
> > >> > > > > > > > >
> > >> > > > > > > > > -- I still have some confusion about how Key
> Generating
> > >> > > > Opertator
> > >> > > > > > and
> > >> > > > > > > > > CepOperator (Pattern Matching & Processing Operator)
> > work
> > >> > > > together.
> > >> > > > > > If
> > >> > > > > > > > > there are N PatternProcessors, will the Key Generating
> > >> > > Opertator
> > >> > > > > > > > generate N
> > >> > > > > > > > > keyedStreams, and then N CepOperator would process
> each
> > >> Key
> > >> > > > > > separately ?
> > >> > > > > > > > Or
> > >> > > > > > > > > every CepOperator Task would process all patterns, if
> > so,
> > >> does
> > >> > > > the
> > >> > > > > > key
> > >> > > > > > > > type
> > >> > > > > > > > > in each PatternProcessor need to be the same?
> > >> > > > > > > > >
> > >> > > > > > > > > Firstly the Pattern Matching & Processing Operator is
> > not
> > >> the
> > >> > > > > > CepOperator
> > >> > > > > > > > > at present, because CepOperator mechanism is based on
> > the
> > >> > > > NFAState.
> > >> > > > > > > > > Secondly if there are N PatternProcessors, the Key
> > >> Generating
> > >> > > > > > Opertator
> > >> > > > > > > > > combines all the keyedStreams with keyBy() operation,
> > >> thus the
> > >> > > > > > Pattern
> > >> > > > > > > > > Matching & Processing Operator would process all the
> > >> patterns.
> > >> > > In
> > >> > > > > > other
> > >> > > > > > > > > words, the KeySelector of the PatternProcessor is used
> > >> for the
> > >> > > > Key
> > >> > > > > > > > > Generating Opertator, and the Pattern and
> > >> > > PatternProceessFunction
> > >> > > > > of
> > >> > > > > > the
> > >> > > > > > > > > PatternProcessor are used for the Pattern Matching &
> > >> Processing
> > >> > > > > > Operator.
> > >> > > > > > > > > Lastly the key type in each PatternProcessor is the
> > same,
> > >> > > > regarded
> > >> > > > > as
> > >> > > > > > > > > Object type.
> > >> > > > > > > > >
> > >> > > > > > > > > -- Maybe need to pay attention to it when implementing
> > it
> > >> .If
> > >> > > > some
> > >> > > > > > > > Pattern
> > >> > > > > > > > > has been removed or updated, will the partially
> matched
> > >> results
> > >> > > > in
> > >> > > > > > > > > StateBackend would be clean up or We rely on state ttl
> > to
> > >> clean
> > >> > > > up
> > >> > > > > > these
> > >> > > > > > > > > expired states.
> > >> > > > > > > > >
> > >> > > > > > > > > If certain Pattern has been removed or updated, the
> > >> partially
> > >> > > > > matched
> > >> > > > > > > > > results in StateBackend would be clean up until the
> next
> > >> > > > > checkpoint.
> > >> > > > > > The
> > >> > > > > > > > > partially matched result doesn't depend on the state
> ttl
> > >> of the
> > >> > > > > > > > > StateBackend.
> > >> > > > > > > > >
> > >> > > > > > > > > 4. Will the PatternProcessorManager keep all the
> active
> > >> > > > > > PatternProcessor
> > >> > > > > > > > > in memory? We have also Support Multiple Rule and
> > Dynamic
> > >> Rule
> > >> > > > > > Changing.
> > >> > > > > > > > > But we are facing such a problem, some users’ usage
> > >> scenarios
> > >> > > are
> > >> > > > > > that
> > >> > > > > > > > they
> > >> > > > > > > > > want to have their own pattern for each user_id, which
> > >> means
> > >> > > that
> > >> > > > > > there
> > >> > > > > > > > > could be thousands of patterns, which would make the
> > >> > > performance
> > >> > > > of
> > >> > > > > > > > Pattern
> > >> > > > > > > > > Matching very poor. We are also trying to solve this
> > >> problem.
> > >> > > > > > > > >
> > >> > > > > > > > > The PatternProcessorManager keeps all the active
> > >> > > PatternProcessor
> > >> > > > > in
> > >> > > > > > > > > memory. For scenarios that they want to have their own
> > >> pattern
> > >> > > > for
> > >> > > > > > each
> > >> > > > > > > > > user_id, IMO, is it possible to reduce the
> fine-grained
> > >> pattern
> > >> > > > of
> > >> > > > > > > > > PatternProcessor to solve the performance problem of
> the
> > >> > > Pattern
> > >> > > > > > > > Matching,
> > >> > > > > > > > > for example, a pattern corresponds to a group of
> users?
> > >> The
> > >> > > > > scenarios
> > >> > > > > > > > > mentioned above need to be solved by case by case.
> > >> > > > > > > > >
> > >> > > > > > > > > Best,
> > >> > > > > > > > > Nicholas Jiang
> > >> > > > > > > > >
> > >> > > > > > > > > On 2021/12/17 11:43:10 yue ma wrote:
> > >> > > > > > > > > > Glad to see the Community's progress in Flink CEP.
> > After
> > >> > > > reading
> > >> > > > > > this
> > >> > > > > > > > > Flip,
> > >> > > > > > > > > > I have few questions, would you please take a look
> ?
> > >> > > > > > > > > >
> > >> > > > > > > > > > 1. About Pattern Updating. If we use
> > >> > > > PatternProcessoerDiscoverer
> > >> > > > > to
> > >> > > > > > > > > update
> > >> > > > > > > > > > the rules, will it increase the load of JM? For
> > >> example, if
> > >> > > the
> > >> > > > > > user
> > >> > > > > > > > > wants
> > >> > > > > > > > > > the updated rule to take effect immediately,, which
> > >> means
> > >> > > that
> > >> > > > we
> > >> > > > > > need
> > >> > > > > > > > to
> > >> > > > > > > > > > set a shorter check interval or there is another
> > >> scenario
> > >> > > when
> > >> > > > > > users
> > >> > > > > > > > > > rarely update the pattern, will the
> > >> > > PatternProcessoerDiscoverer
> > >> > > > > be
> > >> > > > > > in
> > >> > > > > > > > > most
> > >> > > > > > > > > > of the time Do useless checks ? Will a lazy update
> > mode
> > >> could
> > >> > > > be
> > >> > > > > > used,
> > >> > > > > > > > > > which the pattern only be updated when triggered by
> > the
> > >> user,
> > >> > > > and
> > >> > > > > > do
> > >> > > > > > > > > > nothing at other times ?
> > >> > > > > > > > > >
> > >> > > > > > > > > > 2. I still have some confusion about how Key
> > >> Generating
> > >> > > > > > Opertator and
> > >> > > > > > > > > > CepOperator (Pattern Matching & Processing Operator)
> > >> work
> > >> > > > > > together. If
> > >> > > > > > > > > > there are N PatternProcessors, will the Key
> Generating
> > >> > > > Opertator
> > >> > > > > > > > > generate N
> > >> > > > > > > > > > keyedStreams, and then N CepOperator would process
> > each
> > >> Key
> > >> > > > > > separately
> > >> > > > > > > > ?
> > >> > > > > > > > > Or
> > >> > > > > > > > > > every CepOperator Task would process all patterns,
> if
> > >> so,
> > >> > > does
> > >> > > > > the
> > >> > > > > > key
> > >> > > > > > > > > type
> > >> > > > > > > > > > in each PatternProcessor need to be the same ?
> > >> > > > > > > > > >
> > >> > > > > > > > > > 3. Maybe need to pay attention to it when
> implementing
> > >> it .If
> > >> > > > > some
> > >> > > > > > > > > Pattern
> > >> > > > > > > > > > has been removed or updateed ,will the partially
> > >> matched
> > >> > > > results
> > >> > > > > > in
> > >> > > > > > > > > > StateBackend would be clean up or We rely on state
> ttl
> > >> to
> > >> > > clean
> > >> > > > > up
> > >> > > > > > > > these
> > >> > > > > > > > > > expired states.
> > >> > > > > > > > > >
> > >> > > > > > > > > > 4. Will the PatternProcessorManager keep all the
> > active
> > >> > > > > > > > PatternProcessor
> > >> > > > > > > > > in
> > >> > > > > > > > > > memory ? We have also Support Multiple Rule and
> > Dynamic
> > >> Rule
> > >> > > > > > Changing .
> > >> > > > > > > > > > But we are facing such a problem, some users’ usage
> > >> scenarios
> > >> > > > are
> > >> > > > > > that
> > >> > > > > > > > > they
> > >> > > > > > > > > > want to have their own pattern for each user_id,
> which
> > >> means
> > >> > > > that
> > >> > > > > > there
> > >> > > > > > > > > > could be thousands of patterns, which would make the
> > >> > > > performance
> > >> > > > > of
> > >> > > > > > > > > Pattern
> > >> > > > > > > > > > Matching very poor. We are also trying to solve this
> > >> problem.
> > >> > > > > > > > > >
> > >> > > > > > > > > > Yunfeng Zhou <fl...@gmail.com>
> > >> 于2021年12月10日周五
> > >> > > > > 19:16写道：
> > >> > > > > > > > > >
> > >> > > > > > > > > > > Hi all，
> > >> > > > > > > > > > >
> > >> > > > > > > > > > > I'm opening this thread to propose the design to
> > >> support
> > >> > > > > multiple
> > >> > > > > > > > rule
> > >> > > > > > > > > &
> > >> > > > > > > > > > > dynamic rule changing in the Flink-CEP project, as
> > >> > > described
> > >> > > > in
> > >> > > > > > > > > FLIP-200
> > >> > > > > > > > > > > [1]
> > >> > > > > > > > > > > .
> > >> > > > > > > > > > >
> > >> > > > > > > > > > > Currently Flink CEP only supports having a single
> > >> pattern
> > >> > > > > inside
> > >> > > > > > a
> > >> > > > > > > > > > > CepOperator and does not support changing the
> > pattern
> > >> > > > > > dynamically. In
> > >> > > > > > > > > order
> > >> > > > > > > > > > > to reduce resource consumption and to experience
> > >> shorter
> > >> > > > > downtime
> > >> > > > > > > > > during
> > >> > > > > > > > > > > pattern updates, there is a growing need in the
> > >> production
> > >> > > > > > > > environment
> > >> > > > > > > > > that
> > >> > > > > > > > > > > expects CEP to support having multiple patterns in
> > one
> > >> > > > operator
> > >> > > > > > and
> > >> > > > > > > > to
> > >> > > > > > > > > > > support dynamically changing them. Therefore I
> > >> propose to
> > >> > > add
> > >> > > > > > certain
> > >> > > > > > > > > > > infrastructure as described in FLIP-200 to support
> > >> these
> > >> > > > > > > > > functionalities.
> > >> > > > > > > > > > >
> > >> > > > > > > > > > > Please feel free to reply to this email thread.
> > >> Looking
> > >> > > > forward
> > >> > > > > > to
> > >> > > > > > > > your
> > >> > > > > > > > > > > feedback!
> > >> > > > > > > > > > >
> > >> > > > > > > > > > > [1]
> > >> > > > > > > > > > >
> > >> > > > > > > > >
> > >> > > > > > > >
> > >> > > > > >
> > >> > > > >
> > >> > > >
> > >> > >
> > >>
> >
> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=195730308
> > >> > > > > > > > > > >
> > >> > > > > > > > > > > Best regards,
> > >> > > > > > > > > > >
> > >> > > > > > > > > > > Yunfeng
> > >> > > > > > > > > > >
> > >> > > > > > > > > >
> > >> > > > > > > > >
> > >> > > > > > > >
> > >> > > > > > > >
> > >> > > > > > > > --
> > >> > > > > > > >
> > >> > > > > > > > Konstantin Knauf
> > >> > > > > > > >
> > >> > > > > > > > https://twitter.com/snntrable
> > >> > > > > > > >
> > >> > > > > > > > https://github.com/knaufk
> > >> > > > > > > >
> > >> > > > > > >
> > >> > > > > >
> > >> > > > >
> > >> > > >
> > >> > >
> > >> > >
> > >> > > --
> > >> > >
> > >> > > Konstantin Knauf
> > >> > >
> > >> > > https://twitter.com/snntrable
> > >> > >
> > >> > > https://github.com/knaufk
> > >> > >
> > >> >
> > >>
> > >
> >
>