Re: [DISCUSS] KIP-228 Negative record timestamp support

[Ewen Cheslack-Postava <ew...@confluent.io>]

For `allow.negative.timestamps`, do you mean this as a broker config? I'm
not entirely clear on what the proposal would entail.

I think taking into account whether we're talking about compatibility with
existing data in Kafka vs enabling use of negative timestamps is important
here. If they're effectively not supported today (though admittedly this is
really client-specific), then we need only concern ourselves with data that
hasn't been produced into Kafka yet. In that case, we can always handle
sentinel values in special ways if we really want to. For example, the Java
producer does not accept any values < 0 and the API supports passing null
rather than the sentinels. The implementation could easily be made to map
those values into a range that is less likely to be utilized (e.g. use the
values near Long.MIN_VALUE and have the consumer convert back as needed).
The sentinel for NO_TIMESTAMP could be changed between versions as long as
it is handled consistently between client versions.

IMO we already have way too many configs, so we should think about where
the impact is and if a not ideal, but also not significant compromise can
be made and avoid most of the additional complexity. Introducing the new
config seems like it has significant compatibility concerns that need to be
sorted out. In contrast, I suspect the use cases we need to support that
have come up so far can handle 1 or 2 special cases and the necessary
munging could be handled safely by interceptors such that it is trivial to
make sure all your apps do the right thing. I appreciate the pain of a ton
of mailing list questions about an issue like this, but given the
likelihood of encountering that particular value, I just find it unlikely
it would be that common and I think it's a reasonable tradeoff to tell a
user they might need to handle that one special case.

-Ewen

On Thu, Dec 28, 2017 at 12:58 PM, Matthias J. Sax <ma...@confluent.io>
wrote:

> I agree that changing message format or using a flag bit might not be
> worth it.
>
> However, just keeping -1 as "unknown" leaving a time gap give me a lot
> of headache, too. Your arguments about "not an issue in practice" kinda
> make sense to me, but I see the number of question on the mailing list
> already if we really follow this path... It will confuse users that
> don't pay attention and "loose" data if Kafka Streams drops records with
> timestamp -1 but processes other records with negative timestamps.
>
> Thus, I was wondering if a new topic config (maybe
> `allow.negative.timestamps` with default `false`) that allows for enable
> negative timestamps would be the better solution? With this new config,
> we would not have any sentinel value for "unknown" and all timestamps
> would be valid. Old producers, can't write to those topics if they are
> configured with CREATE_TIME though; APPEND_TIME would still work for
> older producers but with APPEND_TIME no negative timestamps are possible
> in the first place, so this config would not have any impact anyway.
>
> Kafka Streams could check the topic config and only drop negative
> timestamps is they are not enabled. Or course, existing topic should not
> enable negative timestamps if there are records with -1 in them already
> -- otherwise, semantics break down -- but this would be a config error
> we cannot prevent. However, I would expect that mostly newly created
> topics would enable this config anyway.
>
>
> -Matthias
>
> On 12/18/17 10:47 PM, Ewen Cheslack-Postava wrote:
> > I think the trivial change of just recognizing using -1 was a mistake
> for a
> > sentinel value and special casing it while allowing other negative values
> > through is the most practical, reasonable change.
> >
> > Realistically, the scope of impact for that -1 is pretty tiny, as has
> been
> > pointed out. A single millisecond gap in available timestamps in 1969.
> For
> > producers that really want to be careful (as the NYT data might want to
> > be), having the producer layer adjust accordingly is unlikely to be an
> > issue (you can't assume these timestamps are unique anyway, so they
> cannot
> > reasonably used for ordering; adjusting by 1ms is a practical tradeoff).
> >
> > Other approaches where we modify the semantics of the timestamp from the
> > two existing modes require eating up valuable flags in the message
> format,
> > or ramping the message format version, all of which make things
> > significantly messier. Hell, timezones, leap seconds, and ms granularity
> > probably make that 1ms window pretty much moot for any practical
> > applications, and for the extremely rare case that an application might
> > care, they are probably willing to pay the cost of a secondary index if
> > they needed to store timestamp values in the payload rather than in the
> > metadata.
> >
> > Given that we have the current system in place, I suspect that any
> > translation to using Long.MIN_VALUE as the sentinel is probably just more
> > confusing to users, adds more implementation overhead to client
> libraries,
> > and is more likely to introduce bugs.
> >
> > Warts like these always feel wrong when approached from pure design
> > principles, but the fact is that the constraints are already there. To
> me,
> > none of the proposals to move to an encoding we'd prefer seem to add
> enough
> > value to outweigh the migration, compatibility, and implementation costs.
> >
> > @Dong -- your point about special timestamp values is a very good one.
> The
> > issue may extend to other cases in the protocol where we use timestamps.
> Is
> > this the scope we need to worry about (2 values instead of just 1) or are
> > there others? This also might be something we want to look out for in the
> > future -- using special values relative to <SignedIntType>.MIN_VALUE
> > instead of relative to 0.
> >
> > -Ewen
> >
> > On Tue, Dec 12, 2017 at 11:12 AM, Dong Lin <li...@gmail.com> wrote:
> >
> >> Hey Konstantin,
> >>
> >> Thanks for updating the KIP.
> >>
> >> If we were to support negative timestamp in the message, we probably
> also
> >> want to support negative timestamp in ListOffsetRequest. Currently in
> >> ListOffsetRequest, timestamp value -2 is used to indicate earliest
> >> timestamp and timestamp value -1 is used to indicate latest timestamp.
> It
> >> seems that we should make changes accordingly so that -1 and -2 can be
> >> supported as valid timestamp in ListOffsetRequest. What do you think?
> >>
> >> Thanks,
> >> Dong
> >>
> >>
> >>
> >> On Mon, Dec 11, 2017 at 12:55 PM, Konstantin Chukhlomin <
> >> chuhlomin@gmail.com
> >>> wrote:
> >>
> >>> Hi all,
> >>>
> >>> I've updated KIP with few more details:
> >>> Added (proposed) Changes in binary message format <
> >>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-228+
> >>> Negative+record+timestamp+support#KIP-228Negativerecordtimes
> >>> tampsupport-Changesinbinarymessageformat>
> >>> Added Changes from producer perspective <https://cwiki.apache.org/conf
> >>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> >>> ort#KIP-228Negativerecordtimestampsupport-
> Changesfromproducerperspective
> >>>
> >>> Added Changes from consumer perspective <https://cwiki.apache.org/conf
> >>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> >>> ort#KIP-228Negativerecordtimestampsupport-
> Changesfromconsumerperspective
> >>>
> >>>
> >>> Let me know if it makes sense to you.
> >>>
> >>> -Konstantin
> >>>
> >>>> On Dec 7, 2017, at 2:46 PM, Konstantin Chukhlomin <
> chuhlomin@gmail.com
> >>>
> >>> wrote:
> >>>>
> >>>> Hi Matthias,
> >>>>
> >>>> Indeed for consumers it will be not obvious what −1 means: actual
> >>> timestamp
> >>>> or no timestamp. Nevertheless, it's just −1 millisecond, so I thought
> >> it
> >>> will be
> >>>> not a big deal to leave it (not clean, but acceptable).
> >>>>
> >>>> I agree that it will much cleaner to have a different type of topics
> >>> that support
> >>>> negative timestamp and/or threat Long.MIN_VALUE as a no-timestamp.
> >>>> I'll update KIP to make it a proposed solution.
> >>>>
> >>>> Thanks,
> >>>> Konstantin
> >>>>
> >>>>> On Dec 5, 2017, at 7:06 PM, Matthias J. Sax <ma...@confluent.io>
> >>> wrote:
> >>>>>
> >>>>> Thanks for the KIP Konstantin.
> >>>>>
> >>>>> From my understanding, you propose to just remove the negative
> >> timestamp
> >>>>> check in KafkaProducer and KafkaStreams. If topics are configured
> with
> >>>>> `CreateTime` brokers also write negative timestamps if they are
> >> embedded
> >>>>> in the message.
> >>>>>
> >>>>> However, I am not sure about the overlapping semantics for -1
> >> timestamp.
> >>>>> My concerns is, that this ambiguity might result in issues. Assume
> >> that
> >>>>> there is a topic (configured with `CreateTime`) for which an old and
> a
> >>>>> new producer are writing. The old producer uses old message format
> and
> >>>>> does not include any timestamp in the message. The broker will
> >> "upgrade"
> >>>>> this message to the new format and set -1. At the same time, the new
> >>>>> producer could write a message with valid timestamp -1. A consumer
> >> could
> >>>>> not distinguish between both cases...
> >>>>>
> >>>>> Also, there might be other Producer implementations that write
> >> negative
> >>>>> timestamps. Thus, those might already exist. For Streams, we don't
> >>>>> process those and we should make sure to keep it this way (to avoid
> >>>>> ambiguity).
> >>>>>
> >>>>> Thus, it might actually make sense to introduce a new timestamp type
> >> to
> >>>>> express those new semantics. The question is still, how to deal with
> >>>>> older producer clients that want to write to those topics.
> >>>>>
> >>>>> - We could either use `Long.MIN_VALUE` as "unknown" (this would be
> way
> >>>>> better than -1 as it's not in the middle of the range but at the very
> >>>>> end and it will also have well-defined semantics).
> >>>>> - Or we use a "mixed-mode" where we use broker wall-clock time for
> >>>>> older message formats (ie, append time semantics for older producers)
> >>>>> - Third, we would even give an error message back to older producers;
> >>>>> this might change the backward compatibility guarantees Kafka
> provides
> >>>>> so far when upgrading brokers. However, this would not affect exiting
> >>>>> topics, but only newly created ones (and we could disallow changing
> >> the
> >>>>> semantics to the new timestamp type to guard against miss
> >>>>> configuration). Thus, it might be ok.
> >>>>>
> >>>>> For Streams, we could check the topic config and process negative
> >>>>> timestamps only if the topic is configures with the new timestamp
> >> type.
> >>>>>
> >>>>>
> >>>>> Maybe I am a little bit to paranoid about overloading -1 semantics.
> >>>>> Curious to get feedback from others.
> >>>>>
> >>>>>
> >>>>>
> >>>>> -Matthias
> >>>>>
> >>>>>
> >>>>> On 12/5/17 1:24 PM, Konstantin Chukhlomin wrote:
> >>>>>> Hi Dong,
> >>>>>>
> >>>>>> Currently we are storing historical timestamp in the message.
> >>>>>>
> >>>>>> What we are trying to achieve is to make it possible to do Kafka
> >> lookup
> >>>>>> by timestamp. Ideally I would do `offsetsForTimes` to find articles
> >>> published
> >>>>>> in 1910s (if we are storing articles on the log).
> >>>>>>
> >>>>>> So first two suggestions aren't really covering our use-case.
> >>>>>>
> >>>>>> We could create a new timestamp type like "HistoricalTimestamp" or
> >>> "MaybeNegativeTimestamp".
> >>>>>> And the only difference between this one and CreateTime is that it
> >>> could be negative.
> >>>>>> I tend to use CreateTime for this purpose because it's easier to
> >>> understand from
> >>>>>> user perspective as a timestamp which publisher can set.
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Konstantin
> >>>>>>
> >>>>>>> On Dec 5, 2017, at 3:47 PM, Dong Lin <li...@gmail.com> wrote:
> >>>>>>>
> >>>>>>> Hey Konstantin,
> >>>>>>>
> >>>>>>> Thanks for the KIP. I have a few questions below.
> >>>>>>>
> >>>>>>> Strictly speaking Kafka actually allows you to store historical
> >> data.
> >>> And
> >>>>>>> user are free to encode arbitrary timestamp field in their Kafka
> >>> message.
> >>>>>>> For example, your Kafka message can currently have Json or Avro
> >>> format and
> >>>>>>> you can put a timestamp field there. Do you think that could
> address
> >>> your
> >>>>>>> use-case?
> >>>>>>>
> >>>>>>> Alternatively, KIP-82 introduced Record Header in Kafka and you can
> >>> also
> >>>>>>> define your customized key/value pair in the header. Do you think
> >>> this can
> >>>>>>> address your use-case?
> >>>>>>>
> >>>>>>> Also, currently there are two types of timestamp according to
> >> KIP-32.
> >>> If
> >>>>>>> the type is LogAppendTime then the timestamp value is the time when
> >>> broker
> >>>>>>> receives the message. If the type is CreateTime then the timestamp
> >>> value is
> >>>>>>> determined when producer produces message. With these two
> >>> definitions, the
> >>>>>>> timestamp should always be positive. We probably need a new type
> >> here
> >>> if we
> >>>>>>> can not put timestamp in the Record Header or the message payload.
> >>> Does
> >>>>>>> this sound reasonable?
> >>>>>>>
> >>>>>>> Thanks,
> >>>>>>> Dong
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> On Tue, Dec 5, 2017 at 8:40 AM, Konstantin Chukhlomin <
> >>> chuhlomin@gmail.com>
> >>>>>>> wrote:
> >>>>>>>
> >>>>>>>> Hi all,
> >>>>>>>>
> >>>>>>>> I have created a KIP to support negative timestamp:
> >>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> >>>>>>>> 228+Negative+record+timestamp+support <https://cwiki.apache.org/
> >>>>>>>> confluence/display/KAFKA/KIP-228+Negative+record+timestamp+
> >> support>
> >>>>>>>>
> >>>>>>>> Here are proposed changes: https://github.com/apache/
> >>>>>>>> kafka/compare/trunk...chuhlomin:trunk <https://github.com/apache/
> >>>>>>>> kafka/compare/trunk...chuhlomin:trunk>
> >>>>>>>>
> >>>>>>>> I'm pretty sure that not cases are covered, so comments and
> >>> suggestions
> >>>>>>>> are welcome.
> >>>>>>>>
> >>>>>>>> Thank you,
> >>>>>>>> Konstantin
> >>>>>>
> >>>>>
> >>>>
> >>>
> >>>
> >>
> >
>
>

Re: [DISCUSS] KIP-228 Negative record timestamp support

[Guozhang Wang <wa...@gmail.com>]

TL.DR: I'd agree with Colin here.


I admit that define -1 == unknown is not a good idea, and if we design the
system from scratch we should not do so.

But Colin's point is valid, that it has been treated like this in past
versions, and I have seen producer client users doing so indeed. So
changing it could potentially break lots of users.

Thinking about this from the user base respective:

1. I'm a happy user as of today and will never use a negative timestamp. I
do not care about this KIP though I do not want to change "-1 ==
unknown" semantics since I'm using it.
2. I'm a happy user that I do not use -1 as well. I will not use negative
timestamps so I do not care about this KIP at all.
3. I'm not happy because I cannot use negative timestamps, I would want
this KIP, while I'm also OK to keep -1 as is knowing it is only a special
case that I will need to work around; think about the most simple hack: one
line change to use 0 or -2 when I want to mean -1.
4. I'm not happy because I cannot use negative timestamps, I would love
this KIP, and I do care about -1 because to me it could be very common or I
would not want to special handle it.

If our expectation that population wise, 2 > 1 >> 3 >> 4, then Colin's
suggestion makes sense to me.

On the other side, I tend to not introduce new configs if their targeted
audience is too small, this is what we learned from core broker configs
that more configs would tend to make users more confused over time.
Although we can argue that for client configs, we have made them on three
levels (HIGH, MEDIUM, LOW) and expect those LOW configs to be of interest
only for a small group of users and hence can be less confusing to normal
users as they'd probably not even pay attention to them, to me this -1 use
case is still too small even for a new LOW level config.





Guozhang



On Tue, Jan 16, 2018 at 1:36 PM, Colin McCabe <cm...@apache.org> wrote:

> I think we should just keep -1 as a special value, and allow negative
> timestamps.  It just means one missing millisecond in 1969, right?
>
> There is just a lot of code everywhere checking for -1, and changing it
> now would be really likely to be buggy.
>
> We probably also want to limit the range of timestamps as well, so that we
> can calculate timestamp1 - timestamp2 without overflowing a 64-bit long.
> If we cap timestamps to be in the range (-2**62,  2**62), we can still
> represent dates about 146 million years into the future or past.
>
> best,
> Colin
>
>
> On Tue, Jan 16, 2018, at 13:03, Konstantin Chukhlomin wrote:
> > Hi all,
> >
> > I tried to summarize below all approaches we were discussing.
> >
> > In case there are some difficulties in email formatting, see GoogleDocs:
> > https://docs.google.com/document/d/1RjlcebpigOj9DyLCedyRxki9nZcFd
> kBchy-k7BiThMc/edit?usp=sharing
> > <https://docs.google.com/document/d/1RjlcebpigOj9DyLCedyRxki9nZcFd
> kBchy-k7BiThMc/edit?usp=sharing>
> >
> > Personally, I find options A01 and A02/B03 very convenient.
> >
> > Please, let me know what you think and feel free to add more options.
> >
> > Thanks,
> > Konstantin
> >
> > –––––––––––––––––––––––––––––––––––––
> >
> > Preconditions:
> > we would need to remote negative timestamp check from producer anyway
> > no existing data should have -1 timestamp unless it is NO_TIMESTAMP
> > older client are not embedding a timestamp: default to -1 on the broker
> side...
> > APPEND_TIME would still work for older producers
> >
> > Can we still use −1 as NO_TIMESTAMP value?
> > Yes: A01 Keep using −1ms as a NO_TIMESTAMP value
> > No, A02 We want to change the semantics of −1ms as an actual timestamp.
> > For example, use Long.MIN_VALUE as "NO_TIMESTAMP".
> > How do we indicate new timestamp format?
> > A02 In the message itself. That way one topic may contain messages of
> > different types.
> > How?
> > B01 Create new timestamp type and use one of the reserved bits
> > B02 Use one reserved bit in the message as a flag
> > B03 Introduce new message format version
> > By the topic property: `allow.negative.timestamp`.
> > That way messages with CreateTime could have negative value.
> > "false" by default for existing topics.
> > Should `allow.negative.timestamp` be enabled by default for new topics?
> > Yes. C01: We want it to be future standard
> > No. C02: We want it to be client specific case by case decision.
> > Do we allow changing that property for existing topics?
> > Yes
> > Yes, but only if existing topic have no records with negative timestamps
> > already
> > No: old behavior and new behavior are not mixed
> > Can old producers write to topics with that flag enabled?
> > Yes, as long as we can differentiate old and new messages: B01-03
> > No, broker will write old "NO_TIMESTAMP" as a −1ms
> > No, broker will throw an error.
> > By the broker config: `allow.negative.timestamp`.
> > What to do with old topics?
> > D01: Convert all messages in all topics to the new format (B01-03)
> > during the update phase.
> > D02: Keep old messages, but write new messages in the new format.
> > D03: Keep old messages, but new topics will have messages with new
> > format.
> > A01 Keep using −1ms as a NO_TIMESTAMP value
> > Cost of change: minimal
> >
> > Pros
> > Cons
> > Realistically, the scope of impact for that -1 is pretty tiny, as has
> > been pointed out. A single millisecond gap in available timestamps in
> > 1969.
> > Keeping -1 as "unknown" leaving a time gap gives a lot of headaches
> >
> > Streams drops records with timestamp -1 but processes other records with
> > negative timestamps which may cause a number of question on the mailing
> > list and will confuse users that don't pay attention and "loose" data.
> > A02 Indicate that message may have negative timestamp in the message
> > itself
> > Cost of change: moderate
> > A03 Add topic config that allows messages with negative timestamp
> > Cost of change: high
> >
> > Kafka Streams could check the topic config and only drop negative
> > timestamps is they are not enabled
> >
> > Pros
> > Cons
> > Relaxes compatibility concerns
> > We already have way too many configs
> >
> > Introducing the new config seems like it has significant compatibility
> > concerns that need to be sorted out.
> > A04 Add broker config that allows messages with negative timestamp
> > Cost of change: high
> > –
> > B01 Add new timestamp type that can be negative
> > Cost of change: moderate
> > Pros
> > Cons
> >
> > Changing message format might not be worth it
> > B02 Use one of reserved bit to indicate negative timestamp (aka flag)
> > Cost of change: moderate
> > Pros
> > Cons
> >
> > Using a flag bit might not be worth it
> > B03 Introduce new message format version
> > Cost of change: low
> >
> > Old producers will still be able to write messages in old version
> > Pros
> > Cons
> > Clear semantics: in new version CreateTime can be negative.
> > Using a flag bit might not be worth it
> >
> > > On Jan 2, 2018, at 11:26 PM, Ewen Cheslack-Postava <ew...@confluent.io>
> wrote:
> > >
> > > On Tue, Jan 2, 2018 at 8:04 PM, Matthias J. Sax <matthias@confluent.io
> >
> > > wrote:
> > >
> > >> I was thinking about a broker/topic config.
> > >>
> > >> However, I am not sure if we only need to worry about data written in
> > >> the future (this would only be true, if there would be no records with
> > >> -1 timestamp already). Assume that we you an existing topic that
> > >> contains data with -1 = UNKNOWN records -- for this case, we would
> give
> > >> those timestamps a new semantics if we suddenly allow negative
> > >> timestamps. (Assuming that we don't allow -1 as a gap in the timeline
> > >> what I would rather not do.)
> > >>
> > >
> > > Using the Java producer you cannot have a negative timestamp today. So
> > > (modulo comment about being dependent on the client implementation), no
> > > existing data should have -1 timestamp unless it is NO_TIMESTAMP.
> > >
> > > When you say you'd rather not like to have -1 as a gap in the
> timeline, can
> > > you explain the potential scale of impact? I view it as a relatively
> > > unlikely value and something that people who are really concerned with
> > > negative timestamps can easily work around. Probably many users won't
> care
> > > as they will not be using pre-1970s data where they actually set the
> Kafka
> > > timestamp (rather than having timestamps embedded in the data) anyway.
> I
> > > agree it isn't ideal, but to me it looks like a reasonable tradeoff.
> What
> > > are the effects/use cases that make you concerned that we'd see
> significant
> > > user pain as a result?
> > >
> > >
> > >>
> > >> Also note, that it's not really client specific IMHO, as one could
> > >> implement their own clients. There are many third party clients and we
> > >> don't know if they check for negative timestamps (applications could
> > >> even assign their own special meaning to negative timestamps as those
> > >> are unused atm) -- furthermore, all older client not embedding a
> > >> timestamp default to -1 on the broker side...
> > >>
> > >
> > > I said "client-specific" because some of the checks are done on the
> > > client-side, which means they are dependent on the specific client
> > > implementation being used. Based on the rest of your comment, I think
> we're
> > > in agreement except for how we are naming things :) I'd have to double
> > > check if the same level of enforcement is done broker-side. I only
> mention
> > > that because we tend to discuss these proposals in the context of only
> the
> > > Java clients, but it is worth thinking through the impact to other
> clients
> > > as well.
> > >
> > >
> > >>
> > >>> The implementation could easily be made to map
> > >>> those values into a range that is less likely to be utilized (e.g.
> use
> > >> the
> > >>> values near Long.MIN_VALUE and have the consumer convert back as
> needed).
> > >>> The sentinel for NO_TIMESTAMP could be changed between versions as
> long
> > >> as
> > >>> it is handled consistently between client versions.
> > >>
> > >> This opens Pandora's box IMHO.
> > >>
> > >
> > > Why? There should be a small number of values that need to be mapped
> and
> > > someone could think through the different compatibility issues that are
> > > possible to determine if there are any significant issues/drawbacks.
> > >
> > >
> > >>
> > >>> Introducing the new
> > >>> config seems like it has significant compatibility concerns that
> need to
> > >> be
> > >>> sorted out.
> > >>
> > >> I cannot follow here -- from my point of view, it relaxes
> compatibility
> > >> concerns. If we only allow new topic to enable negative timestamps,
> old
> > >> behavior and new behavior are not mixed. IMHO, mixing both would be a
> > >> real issue. Thus, for new topics we can change "unknown" from -1 to
> > >> Long.MIN_VALUE and don't mix two different approaches within a single
> > >> topic.
> > >>
> > >
> > > What's the mechanism for this? Is the new config only allowed in
> > > CreateTopics requests? If you use existing tooling to set topic
> configs,
> > > you would just be able to set any valid config. Are the semantics just
> > > undefined if you do? Unless it is impossible to do certain things, we
> have
> > > to deal with the compatibility concerns regardless of intended use.
> Might
> > > be fine to just say the behavior is undefined, but there's still work
> to be
> > > done there. Regardless, I didn't (and probably still don't) have a
> concrete
> > > understanding of the proposed setting, so hard for me to reason about
> it.
> > >
> > > -Ewen
> > >
> > >
> > >>
> > >> I see your point that we do have too many configs -- we could also
> make
> > >> it a new value for existing `message.timestamp.type`.
> > >>
> > >>
> > >> -Matthias
> > >>
> > >>
> > >> On 1/2/18 7:48 PM, Ewen Cheslack-Postava wrote:
> > >>> For `allow.negative.timestamps`, do you mean this as a broker
> config? I'm
> > >>> not entirely clear on what the proposal would entail.
> > >>>
> > >>> I think taking into account whether we're talking about compatibility
> > >> with
> > >>> existing data in Kafka vs enabling use of negative timestamps is
> > >> important
> > >>> here. If they're effectively not supported today (though admittedly
> this
> > >> is
> > >>> really client-specific), then we need only concern ourselves with
> data
> > >> that
> > >>> hasn't been produced into Kafka yet. In that case, we can always
> handle
> > >>> sentinel values in special ways if we really want to. For example,
> the
> > >> Java
> > >>> producer does not accept any values < 0 and the API supports passing
> null
> > >>> rather than the sentinels. The implementation could easily be made
> to map
> > >>> those values into a range that is less likely to be utilized (e.g.
> use
> > >> the
> > >>> values near Long.MIN_VALUE and have the consumer convert back as
> needed).
> > >>> The sentinel for NO_TIMESTAMP could be changed between versions as
> long
> > >> as
> > >>> it is handled consistently between client versions.
> > >>>
> > >>> IMO we already have way too many configs, so we should think about
> where
> > >>> the impact is and if a not ideal, but also not significant
> compromise can
> > >>> be made and avoid most of the additional complexity. Introducing the
> new
> > >>> config seems like it has significant compatibility concerns that
> need to
> > >> be
> > >>> sorted out. In contrast, I suspect the use cases we need to support
> that
> > >>> have come up so far can handle 1 or 2 special cases and the necessary
> > >>> munging could be handled safely by interceptors such that it is
> trivial
> > >> to
> > >>> make sure all your apps do the right thing. I appreciate the pain of
> a
> > >> ton
> > >>> of mailing list questions about an issue like this, but given the
> > >>> likelihood of encountering that particular value, I just find it
> unlikely
> > >>> it would be that common and I think it's a reasonable tradeoff to
> tell a
> > >>> user they might need to handle that one special case.
> > >>>
> > >>> -Ewen
> > >>>
> > >>> On Thu, Dec 28, 2017 at 12:58 PM, Matthias J. Sax <
> matthias@confluent.io
> > >>>
> > >>> wrote:
> > >>>
> > >>>> I agree that changing message format or using a flag bit might not
> be
> > >>>> worth it.
> > >>>>
> > >>>> However, just keeping -1 as "unknown" leaving a time gap give me a
> lot
> > >>>> of headache, too. Your arguments about "not an issue in practice"
> kinda
> > >>>> make sense to me, but I see the number of question on the mailing
> list
> > >>>> already if we really follow this path... It will confuse users that
> > >>>> don't pay attention and "loose" data if Kafka Streams drops records
> with
> > >>>> timestamp -1 but processes other records with negative timestamps.
> > >>>>
> > >>>> Thus, I was wondering if a new topic config (maybe
> > >>>> `allow.negative.timestamps` with default `false`) that allows for
> enable
> > >>>> negative timestamps would be the better solution? With this new
> config,
> > >>>> we would not have any sentinel value for "unknown" and all
> timestamps
> > >>>> would be valid. Old producers, can't write to those topics if they
> are
> > >>>> configured with CREATE_TIME though; APPEND_TIME would still work for
> > >>>> older producers but with APPEND_TIME no negative timestamps are
> possible
> > >>>> in the first place, so this config would not have any impact anyway.
> > >>>>
> > >>>> Kafka Streams could check the topic config and only drop negative
> > >>>> timestamps is they are not enabled. Or course, existing topic
> should not
> > >>>> enable negative timestamps if there are records with -1 in them
> already
> > >>>> -- otherwise, semantics break down -- but this would be a config
> error
> > >>>> we cannot prevent. However, I would expect that mostly newly created
> > >>>> topics would enable this config anyway.
> > >>>>
> > >>>>
> > >>>> -Matthias
> > >>>>
> > >>>> On 12/18/17 10:47 PM, Ewen Cheslack-Postava wrote:
> > >>>>> I think the trivial change of just recognizing using -1 was a
> mistake
> > >>>> for a
> > >>>>> sentinel value and special casing it while allowing other negative
> > >> values
> > >>>>> through is the most practical, reasonable change.
> > >>>>>
> > >>>>> Realistically, the scope of impact for that -1 is pretty tiny, as
> has
> > >>>> been
> > >>>>> pointed out. A single millisecond gap in available timestamps in
> 1969.
> > >>>> For
> > >>>>> producers that really want to be careful (as the NYT data might
> want to
> > >>>>> be), having the producer layer adjust accordingly is unlikely to
> be an
> > >>>>> issue (you can't assume these timestamps are unique anyway, so they
> > >>>> cannot
> > >>>>> reasonably used for ordering; adjusting by 1ms is a practical
> > >> tradeoff).
> > >>>>>
> > >>>>> Other approaches where we modify the semantics of the timestamp
> from
> > >> the
> > >>>>> two existing modes require eating up valuable flags in the message
> > >>>> format,
> > >>>>> or ramping the message format version, all of which make things
> > >>>>> significantly messier. Hell, timezones, leap seconds, and ms
> > >> granularity
> > >>>>> probably make that 1ms window pretty much moot for any practical
> > >>>>> applications, and for the extremely rare case that an application
> might
> > >>>>> care, they are probably willing to pay the cost of a secondary
> index if
> > >>>>> they needed to store timestamp values in the payload rather than
> in the
> > >>>>> metadata.
> > >>>>>
> > >>>>> Given that we have the current system in place, I suspect that any
> > >>>>> translation to using Long.MIN_VALUE as the sentinel is probably
> just
> > >> more
> > >>>>> confusing to users, adds more implementation overhead to client
> > >>>> libraries,
> > >>>>> and is more likely to introduce bugs.
> > >>>>>
> > >>>>> Warts like these always feel wrong when approached from pure design
> > >>>>> principles, but the fact is that the constraints are already
> there. To
> > >>>> me,
> > >>>>> none of the proposals to move to an encoding we'd prefer seem to
> add
> > >>>> enough
> > >>>>> value to outweigh the migration, compatibility, and implementation
> > >> costs.
> > >>>>>
> > >>>>> @Dong -- your point about special timestamp values is a very good
> one.
> > >>>> The
> > >>>>> issue may extend to other cases in the protocol where we use
> > >> timestamps.
> > >>>> Is
> > >>>>> this the scope we need to worry about (2 values instead of just 1)
> or
> > >> are
> > >>>>> there others? This also might be something we want to look out for
> in
> > >> the
> > >>>>> future -- using special values relative to
> <SignedIntType>.MIN_VALUE
> > >>>>> instead of relative to 0.
> > >>>>>
> > >>>>> -Ewen
> > >>>>>
> > >>>>> On Tue, Dec 12, 2017 at 11:12 AM, Dong Lin <li...@gmail.com>
> > >> wrote:
> > >>>>>
> > >>>>>> Hey Konstantin,
> > >>>>>>
> > >>>>>> Thanks for updating the KIP.
> > >>>>>>
> > >>>>>> If we were to support negative timestamp in the message, we
> probably
> > >>>> also
> > >>>>>> want to support negative timestamp in ListOffsetRequest.
> Currently in
> > >>>>>> ListOffsetRequest, timestamp value -2 is used to indicate earliest
> > >>>>>> timestamp and timestamp value -1 is used to indicate latest
> timestamp.
> > >>>> It
> > >>>>>> seems that we should make changes accordingly so that -1 and -2
> can be
> > >>>>>> supported as valid timestamp in ListOffsetRequest. What do you
> think?
> > >>>>>>
> > >>>>>> Thanks,
> > >>>>>> Dong
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>> On Mon, Dec 11, 2017 at 12:55 PM, Konstantin Chukhlomin <
> > >>>>>> chuhlomin@gmail.com
> > >>>>>>> wrote:
> > >>>>>>
> > >>>>>>> Hi all,
> > >>>>>>>
> > >>>>>>> I've updated KIP with few more details:
> > >>>>>>> Added (proposed) Changes in binary message format <
> > >>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-228+
> > >>>>>>> Negative+record+timestamp+support#KIP-228Negativerecordtimes
> > >>>>>>> tampsupport-Changesinbinarymessageformat>
> > >>>>>>> Added Changes from producer perspective <
> > >> https://cwiki.apache.org/conf
> > >>>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> > >>>>>>> ort#KIP-228Negativerecordtimestampsupport-
> > >>>> Changesfromproducerperspective
> > >>>>>>>
> > >>>>>>> Added Changes from consumer perspective <
> > >> https://cwiki.apache.org/conf
> > >>>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> > >>>>>>> ort#KIP-228Negativerecordtimestampsupport-
> > >>>> Changesfromconsumerperspective
> > >>>>>>>
> > >>>>>>>
> > >>>>>>> Let me know if it makes sense to you.
> > >>>>>>>
> > >>>>>>> -Konstantin
> > >>>>>>>
> > >>>>>>>> On Dec 7, 2017, at 2:46 PM, Konstantin Chukhlomin <
> > >>>> chuhlomin@gmail.com
> > >>>>>>>
> > >>>>>>> wrote:
> > >>>>>>>>
> > >>>>>>>> Hi Matthias,
> > >>>>>>>>
> > >>>>>>>> Indeed for consumers it will be not obvious what −1 means:
> actual
> > >>>>>>> timestamp
> > >>>>>>>> or no timestamp. Nevertheless, it's just −1 millisecond, so I
> > >> thought
> > >>>>>> it
> > >>>>>>> will be
> > >>>>>>>> not a big deal to leave it (not clean, but acceptable).
> > >>>>>>>>
> > >>>>>>>> I agree that it will much cleaner to have a different type of
> topics
> > >>>>>>> that support
> > >>>>>>>> negative timestamp and/or threat Long.MIN_VALUE as a
> no-timestamp.
> > >>>>>>>> I'll update KIP to make it a proposed solution.
> > >>>>>>>>
> > >>>>>>>> Thanks,
> > >>>>>>>> Konstantin
> > >>>>>>>>
> > >>>>>>>>> On Dec 5, 2017, at 7:06 PM, Matthias J. Sax <
> matthias@confluent.io
> > >>>
> > >>>>>>> wrote:
> > >>>>>>>>>
> > >>>>>>>>> Thanks for the KIP Konstantin.
> > >>>>>>>>>
> > >>>>>>>>> From my understanding, you propose to just remove the negative
> > >>>>>> timestamp
> > >>>>>>>>> check in KafkaProducer and KafkaStreams. If topics are
> configured
> > >>>> with
> > >>>>>>>>> `CreateTime` brokers also write negative timestamps if they are
> > >>>>>> embedded
> > >>>>>>>>> in the message.
> > >>>>>>>>>
> > >>>>>>>>> However, I am not sure about the overlapping semantics for -1
> > >>>>>> timestamp.
> > >>>>>>>>> My concerns is, that this ambiguity might result in issues.
> Assume
> > >>>>>> that
> > >>>>>>>>> there is a topic (configured with `CreateTime`) for which an
> old
> > >> and
> > >>>> a
> > >>>>>>>>> new producer are writing. The old producer uses old message
> format
> > >>>> and
> > >>>>>>>>> does not include any timestamp in the message. The broker will
> > >>>>>> "upgrade"
> > >>>>>>>>> this message to the new format and set -1. At the same time,
> the
> > >> new
> > >>>>>>>>> producer could write a message with valid timestamp -1. A
> consumer
> > >>>>>> could
> > >>>>>>>>> not distinguish between both cases...
> > >>>>>>>>>
> > >>>>>>>>> Also, there might be other Producer implementations that write
> > >>>>>> negative
> > >>>>>>>>> timestamps. Thus, those might already exist. For Streams, we
> don't
> > >>>>>>>>> process those and we should make sure to keep it this way (to
> avoid
> > >>>>>>>>> ambiguity).
> > >>>>>>>>>
> > >>>>>>>>> Thus, it might actually make sense to introduce a new timestamp
> > >> type
> > >>>>>> to
> > >>>>>>>>> express those new semantics. The question is still, how to deal
> > >> with
> > >>>>>>>>> older producer clients that want to write to those topics.
> > >>>>>>>>>
> > >>>>>>>>> - We could either use `Long.MIN_VALUE` as "unknown" (this
> would be
> > >>>> way
> > >>>>>>>>> better than -1 as it's not in the middle of the range but at
> the
> > >> very
> > >>>>>>>>> end and it will also have well-defined semantics).
> > >>>>>>>>> - Or we use a "mixed-mode" where we use broker wall-clock time
> for
> > >>>>>>>>> older message formats (ie, append time semantics for older
> > >> producers)
> > >>>>>>>>> - Third, we would even give an error message back to older
> > >> producers;
> > >>>>>>>>> this might change the backward compatibility guarantees Kafka
> > >>>> provides
> > >>>>>>>>> so far when upgrading brokers. However, this would not affect
> > >> exiting
> > >>>>>>>>> topics, but only newly created ones (and we could disallow
> changing
> > >>>>>> the
> > >>>>>>>>> semantics to the new timestamp type to guard against miss
> > >>>>>>>>> configuration). Thus, it might be ok.
> > >>>>>>>>>
> > >>>>>>>>> For Streams, we could check the topic config and process
> negative
> > >>>>>>>>> timestamps only if the topic is configures with the new
> timestamp
> > >>>>>> type.
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> Maybe I am a little bit to paranoid about overloading -1
> semantics.
> > >>>>>>>>> Curious to get feedback from others.
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> -Matthias
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> On 12/5/17 1:24 PM, Konstantin Chukhlomin wrote:
> > >>>>>>>>>> Hi Dong,
> > >>>>>>>>>>
> > >>>>>>>>>> Currently we are storing historical timestamp in the message.
> > >>>>>>>>>>
> > >>>>>>>>>> What we are trying to achieve is to make it possible to do
> Kafka
> > >>>>>> lookup
> > >>>>>>>>>> by timestamp. Ideally I would do `offsetsForTimes` to find
> > >> articles
> > >>>>>>> published
> > >>>>>>>>>> in 1910s (if we are storing articles on the log).
> > >>>>>>>>>>
> > >>>>>>>>>> So first two suggestions aren't really covering our use-case.
> > >>>>>>>>>>
> > >>>>>>>>>> We could create a new timestamp type like
> "HistoricalTimestamp" or
> > >>>>>>> "MaybeNegativeTimestamp".
> > >>>>>>>>>> And the only difference between this one and CreateTime is
> that it
> > >>>>>>> could be negative.
> > >>>>>>>>>> I tend to use CreateTime for this purpose because it's easier
> to
> > >>>>>>> understand from
> > >>>>>>>>>> user perspective as a timestamp which publisher can set.
> > >>>>>>>>>>
> > >>>>>>>>>> Thanks,
> > >>>>>>>>>> Konstantin
> > >>>>>>>>>>
> > >>>>>>>>>>> On Dec 5, 2017, at 3:47 PM, Dong Lin <li...@gmail.com>
> > >> wrote:
> > >>>>>>>>>>>
> > >>>>>>>>>>> Hey Konstantin,
> > >>>>>>>>>>>
> > >>>>>>>>>>> Thanks for the KIP. I have a few questions below.
> > >>>>>>>>>>>
> > >>>>>>>>>>> Strictly speaking Kafka actually allows you to store
> historical
> > >>>>>> data.
> > >>>>>>> And
> > >>>>>>>>>>> user are free to encode arbitrary timestamp field in their
> Kafka
> > >>>>>>> message.
> > >>>>>>>>>>> For example, your Kafka message can currently have Json or
> Avro
> > >>>>>>> format and
> > >>>>>>>>>>> you can put a timestamp field there. Do you think that could
> > >>>> address
> > >>>>>>> your
> > >>>>>>>>>>> use-case?
> > >>>>>>>>>>>
> > >>>>>>>>>>> Alternatively, KIP-82 introduced Record Header in Kafka and
> you
> > >> can
> > >>>>>>> also
> > >>>>>>>>>>> define your customized key/value pair in the header. Do you
> think
> > >>>>>>> this can
> > >>>>>>>>>>> address your use-case?
> > >>>>>>>>>>>
> > >>>>>>>>>>> Also, currently there are two types of timestamp according to
> > >>>>>> KIP-32.
> > >>>>>>> If
> > >>>>>>>>>>> the type is LogAppendTime then the timestamp value is the
> time
> > >> when
> > >>>>>>> broker
> > >>>>>>>>>>> receives the message. If the type is CreateTime then the
> > >> timestamp
> > >>>>>>> value is
> > >>>>>>>>>>> determined when producer produces message. With these two
> > >>>>>>> definitions, the
> > >>>>>>>>>>> timestamp should always be positive. We probably need a new
> type
> > >>>>>> here
> > >>>>>>> if we
> > >>>>>>>>>>> can not put timestamp in the Record Header or the message
> > >> payload.
> > >>>>>>> Does
> > >>>>>>>>>>> this sound reasonable?
> > >>>>>>>>>>>
> > >>>>>>>>>>> Thanks,
> > >>>>>>>>>>> Dong
> > >>>>>>>>>>>
> > >>>>>>>>>>>
> > >>>>>>>>>>>
> > >>>>>>>>>>> On Tue, Dec 5, 2017 at 8:40 AM, Konstantin Chukhlomin <
> > >>>>>>> chuhlomin@gmail.com>
> > >>>>>>>>>>> wrote:
> > >>>>>>>>>>>
> > >>>>>>>>>>>> Hi all,
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> I have created a KIP to support negative timestamp:
> > >>>>>>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > >>>>>>>>>>>> 228+Negative+record+timestamp+support <
> > >> https://cwiki.apache.org/
> > >>>>>>>>>>>> confluence/display/KAFKA/KIP-228+Negative+record+timestamp+
> > >>>>>> support>
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> Here are proposed changes: https://github.com/apache/
> > >>>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk <
> > >> https://github.com/apache/
> > >>>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk>
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> I'm pretty sure that not cases are covered, so comments and
> > >>>>>>> suggestions
> > >>>>>>>>>>>> are welcome.
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> Thank you,
> > >>>>>>>>>>>> Konstantin
> > >>>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>
> > >>>>>>>
> > >>>>>>>
> > >>>>>>
> > >>>>>
> > >>>>
> > >>>>
> > >>>
> > >>
> > >>
> >
>



-- 
-- Guozhang

Re: [DISCUSS] KIP-228 Negative record timestamp support

[Colin McCabe <cm...@apache.org>]

I think we should just keep -1 as a special value, and allow negative timestamps.  It just means one missing millisecond in 1969, right?

There is just a lot of code everywhere checking for -1, and changing it now would be really likely to be buggy.

We probably also want to limit the range of timestamps as well, so that we can calculate timestamp1 - timestamp2 without overflowing a 64-bit long.  If we cap timestamps to be in the range (-2**62,  2**62), we can still represent dates about 146 million years into the future or past.

best,
Colin


On Tue, Jan 16, 2018, at 13:03, Konstantin Chukhlomin wrote:
> Hi all,
> 
> I tried to summarize below all approaches we were discussing.
> 
> In case there are some difficulties in email formatting, see GoogleDocs:
> https://docs.google.com/document/d/1RjlcebpigOj9DyLCedyRxki9nZcFdkBchy-k7BiThMc/edit?usp=sharing 
> <https://docs.google.com/document/d/1RjlcebpigOj9DyLCedyRxki9nZcFdkBchy-k7BiThMc/edit?usp=sharing>
> 
> Personally, I find options A01 and A02/B03 very convenient.
> 
> Please, let me know what you think and feel free to add more options.
> 
> Thanks,
> Konstantin
> 
> –––––––––––––––––––––––––––––––––––––
> 
> Preconditions:
> we would need to remote negative timestamp check from producer anyway
> no existing data should have -1 timestamp unless it is NO_TIMESTAMP
> older client are not embedding a timestamp: default to -1 on the broker side...
> APPEND_TIME would still work for older producers
> 
> Can we still use −1 as NO_TIMESTAMP value?
> Yes: A01 Keep using −1ms as a NO_TIMESTAMP value
> No, A02 We want to change the semantics of −1ms as an actual timestamp.
> For example, use Long.MIN_VALUE as "NO_TIMESTAMP".
> How do we indicate new timestamp format?
> A02 In the message itself. That way one topic may contain messages of 
> different types.
> How?
> B01 Create new timestamp type and use one of the reserved bits
> B02 Use one reserved bit in the message as a flag
> B03 Introduce new message format version
> By the topic property: `allow.negative.timestamp`.
> That way messages with CreateTime could have negative value.
> "false" by default for existing topics.
> Should `allow.negative.timestamp` be enabled by default for new topics?
> Yes. C01: We want it to be future standard
> No. C02: We want it to be client specific case by case decision.
> Do we allow changing that property for existing topics?
> Yes
> Yes, but only if existing topic have no records with negative timestamps 
> already
> No: old behavior and new behavior are not mixed
> Can old producers write to topics with that flag enabled?
> Yes, as long as we can differentiate old and new messages: B01-03
> No, broker will write old "NO_TIMESTAMP" as a −1ms
> No, broker will throw an error.
> By the broker config: `allow.negative.timestamp`.
> What to do with old topics?
> D01: Convert all messages in all topics to the new format (B01-03) 
> during the update phase.
> D02: Keep old messages, but write new messages in the new format.
> D03: Keep old messages, but new topics will have messages with new 
> format.
> A01 Keep using −1ms as a NO_TIMESTAMP value
> Cost of change: minimal
> 
> Pros
> Cons
> Realistically, the scope of impact for that -1 is pretty tiny, as has 
> been pointed out. A single millisecond gap in available timestamps in 
> 1969.
> Keeping -1 as "unknown" leaving a time gap gives a lot of headaches
> 
> Streams drops records with timestamp -1 but processes other records with 
> negative timestamps which may cause a number of question on the mailing 
> list and will confuse users that don't pay attention and "loose" data. 
> A02 Indicate that message may have negative timestamp in the message 
> itself
> Cost of change: moderate
> A03 Add topic config that allows messages with negative timestamp
> Cost of change: high
> 
> Kafka Streams could check the topic config and only drop negative 
> timestamps is they are not enabled
> 
> Pros
> Cons
> Relaxes compatibility concerns
> We already have way too many configs
> 
> Introducing the new config seems like it has significant compatibility 
> concerns that need to be sorted out. 
> A04 Add broker config that allows messages with negative timestamp
> Cost of change: high
> –
> B01 Add new timestamp type that can be negative
> Cost of change: moderate
> Pros
> Cons
> 
> Changing message format might not be worth it
> B02 Use one of reserved bit to indicate negative timestamp (aka flag)
> Cost of change: moderate
> Pros
> Cons
> 
> Using a flag bit might not be worth it
> B03 Introduce new message format version
> Cost of change: low
> 
> Old producers will still be able to write messages in old version
> Pros
> Cons
> Clear semantics: in new version CreateTime can be negative.
> Using a flag bit might not be worth it
> 
> > On Jan 2, 2018, at 11:26 PM, Ewen Cheslack-Postava <ew...@confluent.io> wrote:
> > 
> > On Tue, Jan 2, 2018 at 8:04 PM, Matthias J. Sax <ma...@confluent.io>
> > wrote:
> > 
> >> I was thinking about a broker/topic config.
> >> 
> >> However, I am not sure if we only need to worry about data written in
> >> the future (this would only be true, if there would be no records with
> >> -1 timestamp already). Assume that we you an existing topic that
> >> contains data with -1 = UNKNOWN records -- for this case, we would give
> >> those timestamps a new semantics if we suddenly allow negative
> >> timestamps. (Assuming that we don't allow -1 as a gap in the timeline
> >> what I would rather not do.)
> >> 
> > 
> > Using the Java producer you cannot have a negative timestamp today. So
> > (modulo comment about being dependent on the client implementation), no
> > existing data should have -1 timestamp unless it is NO_TIMESTAMP.
> > 
> > When you say you'd rather not like to have -1 as a gap in the timeline, can
> > you explain the potential scale of impact? I view it as a relatively
> > unlikely value and something that people who are really concerned with
> > negative timestamps can easily work around. Probably many users won't care
> > as they will not be using pre-1970s data where they actually set the Kafka
> > timestamp (rather than having timestamps embedded in the data) anyway. I
> > agree it isn't ideal, but to me it looks like a reasonable tradeoff. What
> > are the effects/use cases that make you concerned that we'd see significant
> > user pain as a result?
> > 
> > 
> >> 
> >> Also note, that it's not really client specific IMHO, as one could
> >> implement their own clients. There are many third party clients and we
> >> don't know if they check for negative timestamps (applications could
> >> even assign their own special meaning to negative timestamps as those
> >> are unused atm) -- furthermore, all older client not embedding a
> >> timestamp default to -1 on the broker side...
> >> 
> > 
> > I said "client-specific" because some of the checks are done on the
> > client-side, which means they are dependent on the specific client
> > implementation being used. Based on the rest of your comment, I think we're
> > in agreement except for how we are naming things :) I'd have to double
> > check if the same level of enforcement is done broker-side. I only mention
> > that because we tend to discuss these proposals in the context of only the
> > Java clients, but it is worth thinking through the impact to other clients
> > as well.
> > 
> > 
> >> 
> >>> The implementation could easily be made to map
> >>> those values into a range that is less likely to be utilized (e.g. use
> >> the
> >>> values near Long.MIN_VALUE and have the consumer convert back as needed).
> >>> The sentinel for NO_TIMESTAMP could be changed between versions as long
> >> as
> >>> it is handled consistently between client versions.
> >> 
> >> This opens Pandora's box IMHO.
> >> 
> > 
> > Why? There should be a small number of values that need to be mapped and
> > someone could think through the different compatibility issues that are
> > possible to determine if there are any significant issues/drawbacks.
> > 
> > 
> >> 
> >>> Introducing the new
> >>> config seems like it has significant compatibility concerns that need to
> >> be
> >>> sorted out.
> >> 
> >> I cannot follow here -- from my point of view, it relaxes compatibility
> >> concerns. If we only allow new topic to enable negative timestamps, old
> >> behavior and new behavior are not mixed. IMHO, mixing both would be a
> >> real issue. Thus, for new topics we can change "unknown" from -1 to
> >> Long.MIN_VALUE and don't mix two different approaches within a single
> >> topic.
> >> 
> > 
> > What's the mechanism for this? Is the new config only allowed in
> > CreateTopics requests? If you use existing tooling to set topic configs,
> > you would just be able to set any valid config. Are the semantics just
> > undefined if you do? Unless it is impossible to do certain things, we have
> > to deal with the compatibility concerns regardless of intended use. Might
> > be fine to just say the behavior is undefined, but there's still work to be
> > done there. Regardless, I didn't (and probably still don't) have a concrete
> > understanding of the proposed setting, so hard for me to reason about it.
> > 
> > -Ewen
> > 
> > 
> >> 
> >> I see your point that we do have too many configs -- we could also make
> >> it a new value for existing `message.timestamp.type`.
> >> 
> >> 
> >> -Matthias
> >> 
> >> 
> >> On 1/2/18 7:48 PM, Ewen Cheslack-Postava wrote:
> >>> For `allow.negative.timestamps`, do you mean this as a broker config? I'm
> >>> not entirely clear on what the proposal would entail.
> >>> 
> >>> I think taking into account whether we're talking about compatibility
> >> with
> >>> existing data in Kafka vs enabling use of negative timestamps is
> >> important
> >>> here. If they're effectively not supported today (though admittedly this
> >> is
> >>> really client-specific), then we need only concern ourselves with data
> >> that
> >>> hasn't been produced into Kafka yet. In that case, we can always handle
> >>> sentinel values in special ways if we really want to. For example, the
> >> Java
> >>> producer does not accept any values < 0 and the API supports passing null
> >>> rather than the sentinels. The implementation could easily be made to map
> >>> those values into a range that is less likely to be utilized (e.g. use
> >> the
> >>> values near Long.MIN_VALUE and have the consumer convert back as needed).
> >>> The sentinel for NO_TIMESTAMP could be changed between versions as long
> >> as
> >>> it is handled consistently between client versions.
> >>> 
> >>> IMO we already have way too many configs, so we should think about where
> >>> the impact is and if a not ideal, but also not significant compromise can
> >>> be made and avoid most of the additional complexity. Introducing the new
> >>> config seems like it has significant compatibility concerns that need to
> >> be
> >>> sorted out. In contrast, I suspect the use cases we need to support that
> >>> have come up so far can handle 1 or 2 special cases and the necessary
> >>> munging could be handled safely by interceptors such that it is trivial
> >> to
> >>> make sure all your apps do the right thing. I appreciate the pain of a
> >> ton
> >>> of mailing list questions about an issue like this, but given the
> >>> likelihood of encountering that particular value, I just find it unlikely
> >>> it would be that common and I think it's a reasonable tradeoff to tell a
> >>> user they might need to handle that one special case.
> >>> 
> >>> -Ewen
> >>> 
> >>> On Thu, Dec 28, 2017 at 12:58 PM, Matthias J. Sax <matthias@confluent.io
> >>> 
> >>> wrote:
> >>> 
> >>>> I agree that changing message format or using a flag bit might not be
> >>>> worth it.
> >>>> 
> >>>> However, just keeping -1 as "unknown" leaving a time gap give me a lot
> >>>> of headache, too. Your arguments about "not an issue in practice" kinda
> >>>> make sense to me, but I see the number of question on the mailing list
> >>>> already if we really follow this path... It will confuse users that
> >>>> don't pay attention and "loose" data if Kafka Streams drops records with
> >>>> timestamp -1 but processes other records with negative timestamps.
> >>>> 
> >>>> Thus, I was wondering if a new topic config (maybe
> >>>> `allow.negative.timestamps` with default `false`) that allows for enable
> >>>> negative timestamps would be the better solution? With this new config,
> >>>> we would not have any sentinel value for "unknown" and all timestamps
> >>>> would be valid. Old producers, can't write to those topics if they are
> >>>> configured with CREATE_TIME though; APPEND_TIME would still work for
> >>>> older producers but with APPEND_TIME no negative timestamps are possible
> >>>> in the first place, so this config would not have any impact anyway.
> >>>> 
> >>>> Kafka Streams could check the topic config and only drop negative
> >>>> timestamps is they are not enabled. Or course, existing topic should not
> >>>> enable negative timestamps if there are records with -1 in them already
> >>>> -- otherwise, semantics break down -- but this would be a config error
> >>>> we cannot prevent. However, I would expect that mostly newly created
> >>>> topics would enable this config anyway.
> >>>> 
> >>>> 
> >>>> -Matthias
> >>>> 
> >>>> On 12/18/17 10:47 PM, Ewen Cheslack-Postava wrote:
> >>>>> I think the trivial change of just recognizing using -1 was a mistake
> >>>> for a
> >>>>> sentinel value and special casing it while allowing other negative
> >> values
> >>>>> through is the most practical, reasonable change.
> >>>>> 
> >>>>> Realistically, the scope of impact for that -1 is pretty tiny, as has
> >>>> been
> >>>>> pointed out. A single millisecond gap in available timestamps in 1969.
> >>>> For
> >>>>> producers that really want to be careful (as the NYT data might want to
> >>>>> be), having the producer layer adjust accordingly is unlikely to be an
> >>>>> issue (you can't assume these timestamps are unique anyway, so they
> >>>> cannot
> >>>>> reasonably used for ordering; adjusting by 1ms is a practical
> >> tradeoff).
> >>>>> 
> >>>>> Other approaches where we modify the semantics of the timestamp from
> >> the
> >>>>> two existing modes require eating up valuable flags in the message
> >>>> format,
> >>>>> or ramping the message format version, all of which make things
> >>>>> significantly messier. Hell, timezones, leap seconds, and ms
> >> granularity
> >>>>> probably make that 1ms window pretty much moot for any practical
> >>>>> applications, and for the extremely rare case that an application might
> >>>>> care, they are probably willing to pay the cost of a secondary index if
> >>>>> they needed to store timestamp values in the payload rather than in the
> >>>>> metadata.
> >>>>> 
> >>>>> Given that we have the current system in place, I suspect that any
> >>>>> translation to using Long.MIN_VALUE as the sentinel is probably just
> >> more
> >>>>> confusing to users, adds more implementation overhead to client
> >>>> libraries,
> >>>>> and is more likely to introduce bugs.
> >>>>> 
> >>>>> Warts like these always feel wrong when approached from pure design
> >>>>> principles, but the fact is that the constraints are already there. To
> >>>> me,
> >>>>> none of the proposals to move to an encoding we'd prefer seem to add
> >>>> enough
> >>>>> value to outweigh the migration, compatibility, and implementation
> >> costs.
> >>>>> 
> >>>>> @Dong -- your point about special timestamp values is a very good one.
> >>>> The
> >>>>> issue may extend to other cases in the protocol where we use
> >> timestamps.
> >>>> Is
> >>>>> this the scope we need to worry about (2 values instead of just 1) or
> >> are
> >>>>> there others? This also might be something we want to look out for in
> >> the
> >>>>> future -- using special values relative to <SignedIntType>.MIN_VALUE
> >>>>> instead of relative to 0.
> >>>>> 
> >>>>> -Ewen
> >>>>> 
> >>>>> On Tue, Dec 12, 2017 at 11:12 AM, Dong Lin <li...@gmail.com>
> >> wrote:
> >>>>> 
> >>>>>> Hey Konstantin,
> >>>>>> 
> >>>>>> Thanks for updating the KIP.
> >>>>>> 
> >>>>>> If we were to support negative timestamp in the message, we probably
> >>>> also
> >>>>>> want to support negative timestamp in ListOffsetRequest. Currently in
> >>>>>> ListOffsetRequest, timestamp value -2 is used to indicate earliest
> >>>>>> timestamp and timestamp value -1 is used to indicate latest timestamp.
> >>>> It
> >>>>>> seems that we should make changes accordingly so that -1 and -2 can be
> >>>>>> supported as valid timestamp in ListOffsetRequest. What do you think?
> >>>>>> 
> >>>>>> Thanks,
> >>>>>> Dong
> >>>>>> 
> >>>>>> 
> >>>>>> 
> >>>>>> On Mon, Dec 11, 2017 at 12:55 PM, Konstantin Chukhlomin <
> >>>>>> chuhlomin@gmail.com
> >>>>>>> wrote:
> >>>>>> 
> >>>>>>> Hi all,
> >>>>>>> 
> >>>>>>> I've updated KIP with few more details:
> >>>>>>> Added (proposed) Changes in binary message format <
> >>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-228+
> >>>>>>> Negative+record+timestamp+support#KIP-228Negativerecordtimes
> >>>>>>> tampsupport-Changesinbinarymessageformat>
> >>>>>>> Added Changes from producer perspective <
> >> https://cwiki.apache.org/conf
> >>>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> >>>>>>> ort#KIP-228Negativerecordtimestampsupport-
> >>>> Changesfromproducerperspective
> >>>>>>> 
> >>>>>>> Added Changes from consumer perspective <
> >> https://cwiki.apache.org/conf
> >>>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> >>>>>>> ort#KIP-228Negativerecordtimestampsupport-
> >>>> Changesfromconsumerperspective
> >>>>>>> 
> >>>>>>> 
> >>>>>>> Let me know if it makes sense to you.
> >>>>>>> 
> >>>>>>> -Konstantin
> >>>>>>> 
> >>>>>>>> On Dec 7, 2017, at 2:46 PM, Konstantin Chukhlomin <
> >>>> chuhlomin@gmail.com
> >>>>>>> 
> >>>>>>> wrote:
> >>>>>>>> 
> >>>>>>>> Hi Matthias,
> >>>>>>>> 
> >>>>>>>> Indeed for consumers it will be not obvious what −1 means: actual
> >>>>>>> timestamp
> >>>>>>>> or no timestamp. Nevertheless, it's just −1 millisecond, so I
> >> thought
> >>>>>> it
> >>>>>>> will be
> >>>>>>>> not a big deal to leave it (not clean, but acceptable).
> >>>>>>>> 
> >>>>>>>> I agree that it will much cleaner to have a different type of topics
> >>>>>>> that support
> >>>>>>>> negative timestamp and/or threat Long.MIN_VALUE as a no-timestamp.
> >>>>>>>> I'll update KIP to make it a proposed solution.
> >>>>>>>> 
> >>>>>>>> Thanks,
> >>>>>>>> Konstantin
> >>>>>>>> 
> >>>>>>>>> On Dec 5, 2017, at 7:06 PM, Matthias J. Sax <matthias@confluent.io
> >>> 
> >>>>>>> wrote:
> >>>>>>>>> 
> >>>>>>>>> Thanks for the KIP Konstantin.
> >>>>>>>>> 
> >>>>>>>>> From my understanding, you propose to just remove the negative
> >>>>>> timestamp
> >>>>>>>>> check in KafkaProducer and KafkaStreams. If topics are configured
> >>>> with
> >>>>>>>>> `CreateTime` brokers also write negative timestamps if they are
> >>>>>> embedded
> >>>>>>>>> in the message.
> >>>>>>>>> 
> >>>>>>>>> However, I am not sure about the overlapping semantics for -1
> >>>>>> timestamp.
> >>>>>>>>> My concerns is, that this ambiguity might result in issues. Assume
> >>>>>> that
> >>>>>>>>> there is a topic (configured with `CreateTime`) for which an old
> >> and
> >>>> a
> >>>>>>>>> new producer are writing. The old producer uses old message format
> >>>> and
> >>>>>>>>> does not include any timestamp in the message. The broker will
> >>>>>> "upgrade"
> >>>>>>>>> this message to the new format and set -1. At the same time, the
> >> new
> >>>>>>>>> producer could write a message with valid timestamp -1. A consumer
> >>>>>> could
> >>>>>>>>> not distinguish between both cases...
> >>>>>>>>> 
> >>>>>>>>> Also, there might be other Producer implementations that write
> >>>>>> negative
> >>>>>>>>> timestamps. Thus, those might already exist. For Streams, we don't
> >>>>>>>>> process those and we should make sure to keep it this way (to avoid
> >>>>>>>>> ambiguity).
> >>>>>>>>> 
> >>>>>>>>> Thus, it might actually make sense to introduce a new timestamp
> >> type
> >>>>>> to
> >>>>>>>>> express those new semantics. The question is still, how to deal
> >> with
> >>>>>>>>> older producer clients that want to write to those topics.
> >>>>>>>>> 
> >>>>>>>>> - We could either use `Long.MIN_VALUE` as "unknown" (this would be
> >>>> way
> >>>>>>>>> better than -1 as it's not in the middle of the range but at the
> >> very
> >>>>>>>>> end and it will also have well-defined semantics).
> >>>>>>>>> - Or we use a "mixed-mode" where we use broker wall-clock time for
> >>>>>>>>> older message formats (ie, append time semantics for older
> >> producers)
> >>>>>>>>> - Third, we would even give an error message back to older
> >> producers;
> >>>>>>>>> this might change the backward compatibility guarantees Kafka
> >>>> provides
> >>>>>>>>> so far when upgrading brokers. However, this would not affect
> >> exiting
> >>>>>>>>> topics, but only newly created ones (and we could disallow changing
> >>>>>> the
> >>>>>>>>> semantics to the new timestamp type to guard against miss
> >>>>>>>>> configuration). Thus, it might be ok.
> >>>>>>>>> 
> >>>>>>>>> For Streams, we could check the topic config and process negative
> >>>>>>>>> timestamps only if the topic is configures with the new timestamp
> >>>>>> type.
> >>>>>>>>> 
> >>>>>>>>> 
> >>>>>>>>> Maybe I am a little bit to paranoid about overloading -1 semantics.
> >>>>>>>>> Curious to get feedback from others.
> >>>>>>>>> 
> >>>>>>>>> 
> >>>>>>>>> 
> >>>>>>>>> -Matthias
> >>>>>>>>> 
> >>>>>>>>> 
> >>>>>>>>> On 12/5/17 1:24 PM, Konstantin Chukhlomin wrote:
> >>>>>>>>>> Hi Dong,
> >>>>>>>>>> 
> >>>>>>>>>> Currently we are storing historical timestamp in the message.
> >>>>>>>>>> 
> >>>>>>>>>> What we are trying to achieve is to make it possible to do Kafka
> >>>>>> lookup
> >>>>>>>>>> by timestamp. Ideally I would do `offsetsForTimes` to find
> >> articles
> >>>>>>> published
> >>>>>>>>>> in 1910s (if we are storing articles on the log).
> >>>>>>>>>> 
> >>>>>>>>>> So first two suggestions aren't really covering our use-case.
> >>>>>>>>>> 
> >>>>>>>>>> We could create a new timestamp type like "HistoricalTimestamp" or
> >>>>>>> "MaybeNegativeTimestamp".
> >>>>>>>>>> And the only difference between this one and CreateTime is that it
> >>>>>>> could be negative.
> >>>>>>>>>> I tend to use CreateTime for this purpose because it's easier to
> >>>>>>> understand from
> >>>>>>>>>> user perspective as a timestamp which publisher can set.
> >>>>>>>>>> 
> >>>>>>>>>> Thanks,
> >>>>>>>>>> Konstantin
> >>>>>>>>>> 
> >>>>>>>>>>> On Dec 5, 2017, at 3:47 PM, Dong Lin <li...@gmail.com>
> >> wrote:
> >>>>>>>>>>> 
> >>>>>>>>>>> Hey Konstantin,
> >>>>>>>>>>> 
> >>>>>>>>>>> Thanks for the KIP. I have a few questions below.
> >>>>>>>>>>> 
> >>>>>>>>>>> Strictly speaking Kafka actually allows you to store historical
> >>>>>> data.
> >>>>>>> And
> >>>>>>>>>>> user are free to encode arbitrary timestamp field in their Kafka
> >>>>>>> message.
> >>>>>>>>>>> For example, your Kafka message can currently have Json or Avro
> >>>>>>> format and
> >>>>>>>>>>> you can put a timestamp field there. Do you think that could
> >>>> address
> >>>>>>> your
> >>>>>>>>>>> use-case?
> >>>>>>>>>>> 
> >>>>>>>>>>> Alternatively, KIP-82 introduced Record Header in Kafka and you
> >> can
> >>>>>>> also
> >>>>>>>>>>> define your customized key/value pair in the header. Do you think
> >>>>>>> this can
> >>>>>>>>>>> address your use-case?
> >>>>>>>>>>> 
> >>>>>>>>>>> Also, currently there are two types of timestamp according to
> >>>>>> KIP-32.
> >>>>>>> If
> >>>>>>>>>>> the type is LogAppendTime then the timestamp value is the time
> >> when
> >>>>>>> broker
> >>>>>>>>>>> receives the message. If the type is CreateTime then the
> >> timestamp
> >>>>>>> value is
> >>>>>>>>>>> determined when producer produces message. With these two
> >>>>>>> definitions, the
> >>>>>>>>>>> timestamp should always be positive. We probably need a new type
> >>>>>> here
> >>>>>>> if we
> >>>>>>>>>>> can not put timestamp in the Record Header or the message
> >> payload.
> >>>>>>> Does
> >>>>>>>>>>> this sound reasonable?
> >>>>>>>>>>> 
> >>>>>>>>>>> Thanks,
> >>>>>>>>>>> Dong
> >>>>>>>>>>> 
> >>>>>>>>>>> 
> >>>>>>>>>>> 
> >>>>>>>>>>> On Tue, Dec 5, 2017 at 8:40 AM, Konstantin Chukhlomin <
> >>>>>>> chuhlomin@gmail.com>
> >>>>>>>>>>> wrote:
> >>>>>>>>>>> 
> >>>>>>>>>>>> Hi all,
> >>>>>>>>>>>> 
> >>>>>>>>>>>> I have created a KIP to support negative timestamp:
> >>>>>>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> >>>>>>>>>>>> 228+Negative+record+timestamp+support <
> >> https://cwiki.apache.org/
> >>>>>>>>>>>> confluence/display/KAFKA/KIP-228+Negative+record+timestamp+
> >>>>>> support>
> >>>>>>>>>>>> 
> >>>>>>>>>>>> Here are proposed changes: https://github.com/apache/
> >>>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk <
> >> https://github.com/apache/
> >>>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk>
> >>>>>>>>>>>> 
> >>>>>>>>>>>> I'm pretty sure that not cases are covered, so comments and
> >>>>>>> suggestions
> >>>>>>>>>>>> are welcome.
> >>>>>>>>>>>> 
> >>>>>>>>>>>> Thank you,
> >>>>>>>>>>>> Konstantin
> >>>>>>>>>> 
> >>>>>>>>> 
> >>>>>>>> 
> >>>>>>> 
> >>>>>>> 
> >>>>>> 
> >>>>> 
> >>>> 
> >>>> 
> >>> 
> >> 
> >> 
> 

Re: [DISCUSS] KIP-228 Negative record timestamp support

[Konstantin Chukhlomin <ch...@gmail.com>]

Hi all,

I tried to summarize below all approaches we were discussing.

In case there are some difficulties in email formatting, see GoogleDocs:
https://docs.google.com/document/d/1RjlcebpigOj9DyLCedyRxki9nZcFdkBchy-k7BiThMc/edit?usp=sharing <https://docs.google.com/document/d/1RjlcebpigOj9DyLCedyRxki9nZcFdkBchy-k7BiThMc/edit?usp=sharing>

Personally, I find options A01 and A02/B03 very convenient.

Please, let me know what you think and feel free to add more options.

Thanks,
Konstantin

–––––––––––––––––––––––––––––––––––––

Preconditions:
we would need to remote negative timestamp check from producer anyway
no existing data should have -1 timestamp unless it is NO_TIMESTAMP
older client are not embedding a timestamp: default to -1 on the broker side...
APPEND_TIME would still work for older producers

Can we still use −1 as NO_TIMESTAMP value?
Yes: A01 Keep using −1ms as a NO_TIMESTAMP value
No, A02 We want to change the semantics of −1ms as an actual timestamp.
For example, use Long.MIN_VALUE as "NO_TIMESTAMP".
How do we indicate new timestamp format?
A02 In the message itself. That way one topic may contain messages of different types.
How?
B01 Create new timestamp type and use one of the reserved bits
B02 Use one reserved bit in the message as a flag
B03 Introduce new message format version
By the topic property: `allow.negative.timestamp`.
That way messages with CreateTime could have negative value.
"false" by default for existing topics.
Should `allow.negative.timestamp` be enabled by default for new topics?
Yes. C01: We want it to be future standard
No. C02: We want it to be client specific case by case decision.
Do we allow changing that property for existing topics?
Yes
Yes, but only if existing topic have no records with negative timestamps already
No: old behavior and new behavior are not mixed
Can old producers write to topics with that flag enabled?
Yes, as long as we can differentiate old and new messages: B01-03
No, broker will write old "NO_TIMESTAMP" as a −1ms
No, broker will throw an error.
By the broker config: `allow.negative.timestamp`.
What to do with old topics?
D01: Convert all messages in all topics to the new format (B01-03) during the update phase.
D02: Keep old messages, but write new messages in the new format.
D03: Keep old messages, but new topics will have messages with new format.
A01 Keep using −1ms as a NO_TIMESTAMP value
Cost of change: minimal

Pros
Cons
Realistically, the scope of impact for that -1 is pretty tiny, as has been pointed out. A single millisecond gap in available timestamps in 1969.
Keeping -1 as "unknown" leaving a time gap gives a lot of headaches

Streams drops records with timestamp -1 but processes other records with negative timestamps which may cause a number of question on the mailing list and will confuse users that don't pay attention and "loose" data. 
A02 Indicate that message may have negative timestamp in the message itself
Cost of change: moderate
A03 Add topic config that allows messages with negative timestamp
Cost of change: high

Kafka Streams could check the topic config and only drop negative timestamps is they are not enabled

Pros
Cons
Relaxes compatibility concerns
We already have way too many configs

Introducing the new config seems like it has significant compatibility concerns that need to be sorted out. 
A04 Add broker config that allows messages with negative timestamp
Cost of change: high
–
B01 Add new timestamp type that can be negative
Cost of change: moderate
Pros
Cons

Changing message format might not be worth it
B02 Use one of reserved bit to indicate negative timestamp (aka flag)
Cost of change: moderate
Pros
Cons

Using a flag bit might not be worth it
B03 Introduce new message format version
Cost of change: low

Old producers will still be able to write messages in old version
Pros
Cons
Clear semantics: in new version CreateTime can be negative.
Using a flag bit might not be worth it

> On Jan 2, 2018, at 11:26 PM, Ewen Cheslack-Postava <ew...@confluent.io> wrote:
> 
> On Tue, Jan 2, 2018 at 8:04 PM, Matthias J. Sax <ma...@confluent.io>
> wrote:
> 
>> I was thinking about a broker/topic config.
>> 
>> However, I am not sure if we only need to worry about data written in
>> the future (this would only be true, if there would be no records with
>> -1 timestamp already). Assume that we you an existing topic that
>> contains data with -1 = UNKNOWN records -- for this case, we would give
>> those timestamps a new semantics if we suddenly allow negative
>> timestamps. (Assuming that we don't allow -1 as a gap in the timeline
>> what I would rather not do.)
>> 
> 
> Using the Java producer you cannot have a negative timestamp today. So
> (modulo comment about being dependent on the client implementation), no
> existing data should have -1 timestamp unless it is NO_TIMESTAMP.
> 
> When you say you'd rather not like to have -1 as a gap in the timeline, can
> you explain the potential scale of impact? I view it as a relatively
> unlikely value and something that people who are really concerned with
> negative timestamps can easily work around. Probably many users won't care
> as they will not be using pre-1970s data where they actually set the Kafka
> timestamp (rather than having timestamps embedded in the data) anyway. I
> agree it isn't ideal, but to me it looks like a reasonable tradeoff. What
> are the effects/use cases that make you concerned that we'd see significant
> user pain as a result?
> 
> 
>> 
>> Also note, that it's not really client specific IMHO, as one could
>> implement their own clients. There are many third party clients and we
>> don't know if they check for negative timestamps (applications could
>> even assign their own special meaning to negative timestamps as those
>> are unused atm) -- furthermore, all older client not embedding a
>> timestamp default to -1 on the broker side...
>> 
> 
> I said "client-specific" because some of the checks are done on the
> client-side, which means they are dependent on the specific client
> implementation being used. Based on the rest of your comment, I think we're
> in agreement except for how we are naming things :) I'd have to double
> check if the same level of enforcement is done broker-side. I only mention
> that because we tend to discuss these proposals in the context of only the
> Java clients, but it is worth thinking through the impact to other clients
> as well.
> 
> 
>> 
>>> The implementation could easily be made to map
>>> those values into a range that is less likely to be utilized (e.g. use
>> the
>>> values near Long.MIN_VALUE and have the consumer convert back as needed).
>>> The sentinel for NO_TIMESTAMP could be changed between versions as long
>> as
>>> it is handled consistently between client versions.
>> 
>> This opens Pandora's box IMHO.
>> 
> 
> Why? There should be a small number of values that need to be mapped and
> someone could think through the different compatibility issues that are
> possible to determine if there are any significant issues/drawbacks.
> 
> 
>> 
>>> Introducing the new
>>> config seems like it has significant compatibility concerns that need to
>> be
>>> sorted out.
>> 
>> I cannot follow here -- from my point of view, it relaxes compatibility
>> concerns. If we only allow new topic to enable negative timestamps, old
>> behavior and new behavior are not mixed. IMHO, mixing both would be a
>> real issue. Thus, for new topics we can change "unknown" from -1 to
>> Long.MIN_VALUE and don't mix two different approaches within a single
>> topic.
>> 
> 
> What's the mechanism for this? Is the new config only allowed in
> CreateTopics requests? If you use existing tooling to set topic configs,
> you would just be able to set any valid config. Are the semantics just
> undefined if you do? Unless it is impossible to do certain things, we have
> to deal with the compatibility concerns regardless of intended use. Might
> be fine to just say the behavior is undefined, but there's still work to be
> done there. Regardless, I didn't (and probably still don't) have a concrete
> understanding of the proposed setting, so hard for me to reason about it.
> 
> -Ewen
> 
> 
>> 
>> I see your point that we do have too many configs -- we could also make
>> it a new value for existing `message.timestamp.type`.
>> 
>> 
>> -Matthias
>> 
>> 
>> On 1/2/18 7:48 PM, Ewen Cheslack-Postava wrote:
>>> For `allow.negative.timestamps`, do you mean this as a broker config? I'm
>>> not entirely clear on what the proposal would entail.
>>> 
>>> I think taking into account whether we're talking about compatibility
>> with
>>> existing data in Kafka vs enabling use of negative timestamps is
>> important
>>> here. If they're effectively not supported today (though admittedly this
>> is
>>> really client-specific), then we need only concern ourselves with data
>> that
>>> hasn't been produced into Kafka yet. In that case, we can always handle
>>> sentinel values in special ways if we really want to. For example, the
>> Java
>>> producer does not accept any values < 0 and the API supports passing null
>>> rather than the sentinels. The implementation could easily be made to map
>>> those values into a range that is less likely to be utilized (e.g. use
>> the
>>> values near Long.MIN_VALUE and have the consumer convert back as needed).
>>> The sentinel for NO_TIMESTAMP could be changed between versions as long
>> as
>>> it is handled consistently between client versions.
>>> 
>>> IMO we already have way too many configs, so we should think about where
>>> the impact is and if a not ideal, but also not significant compromise can
>>> be made and avoid most of the additional complexity. Introducing the new
>>> config seems like it has significant compatibility concerns that need to
>> be
>>> sorted out. In contrast, I suspect the use cases we need to support that
>>> have come up so far can handle 1 or 2 special cases and the necessary
>>> munging could be handled safely by interceptors such that it is trivial
>> to
>>> make sure all your apps do the right thing. I appreciate the pain of a
>> ton
>>> of mailing list questions about an issue like this, but given the
>>> likelihood of encountering that particular value, I just find it unlikely
>>> it would be that common and I think it's a reasonable tradeoff to tell a
>>> user they might need to handle that one special case.
>>> 
>>> -Ewen
>>> 
>>> On Thu, Dec 28, 2017 at 12:58 PM, Matthias J. Sax <matthias@confluent.io
>>> 
>>> wrote:
>>> 
>>>> I agree that changing message format or using a flag bit might not be
>>>> worth it.
>>>> 
>>>> However, just keeping -1 as "unknown" leaving a time gap give me a lot
>>>> of headache, too. Your arguments about "not an issue in practice" kinda
>>>> make sense to me, but I see the number of question on the mailing list
>>>> already if we really follow this path... It will confuse users that
>>>> don't pay attention and "loose" data if Kafka Streams drops records with
>>>> timestamp -1 but processes other records with negative timestamps.
>>>> 
>>>> Thus, I was wondering if a new topic config (maybe
>>>> `allow.negative.timestamps` with default `false`) that allows for enable
>>>> negative timestamps would be the better solution? With this new config,
>>>> we would not have any sentinel value for "unknown" and all timestamps
>>>> would be valid. Old producers, can't write to those topics if they are
>>>> configured with CREATE_TIME though; APPEND_TIME would still work for
>>>> older producers but with APPEND_TIME no negative timestamps are possible
>>>> in the first place, so this config would not have any impact anyway.
>>>> 
>>>> Kafka Streams could check the topic config and only drop negative
>>>> timestamps is they are not enabled. Or course, existing topic should not
>>>> enable negative timestamps if there are records with -1 in them already
>>>> -- otherwise, semantics break down -- but this would be a config error
>>>> we cannot prevent. However, I would expect that mostly newly created
>>>> topics would enable this config anyway.
>>>> 
>>>> 
>>>> -Matthias
>>>> 
>>>> On 12/18/17 10:47 PM, Ewen Cheslack-Postava wrote:
>>>>> I think the trivial change of just recognizing using -1 was a mistake
>>>> for a
>>>>> sentinel value and special casing it while allowing other negative
>> values
>>>>> through is the most practical, reasonable change.
>>>>> 
>>>>> Realistically, the scope of impact for that -1 is pretty tiny, as has
>>>> been
>>>>> pointed out. A single millisecond gap in available timestamps in 1969.
>>>> For
>>>>> producers that really want to be careful (as the NYT data might want to
>>>>> be), having the producer layer adjust accordingly is unlikely to be an
>>>>> issue (you can't assume these timestamps are unique anyway, so they
>>>> cannot
>>>>> reasonably used for ordering; adjusting by 1ms is a practical
>> tradeoff).
>>>>> 
>>>>> Other approaches where we modify the semantics of the timestamp from
>> the
>>>>> two existing modes require eating up valuable flags in the message
>>>> format,
>>>>> or ramping the message format version, all of which make things
>>>>> significantly messier. Hell, timezones, leap seconds, and ms
>> granularity
>>>>> probably make that 1ms window pretty much moot for any practical
>>>>> applications, and for the extremely rare case that an application might
>>>>> care, they are probably willing to pay the cost of a secondary index if
>>>>> they needed to store timestamp values in the payload rather than in the
>>>>> metadata.
>>>>> 
>>>>> Given that we have the current system in place, I suspect that any
>>>>> translation to using Long.MIN_VALUE as the sentinel is probably just
>> more
>>>>> confusing to users, adds more implementation overhead to client
>>>> libraries,
>>>>> and is more likely to introduce bugs.
>>>>> 
>>>>> Warts like these always feel wrong when approached from pure design
>>>>> principles, but the fact is that the constraints are already there. To
>>>> me,
>>>>> none of the proposals to move to an encoding we'd prefer seem to add
>>>> enough
>>>>> value to outweigh the migration, compatibility, and implementation
>> costs.
>>>>> 
>>>>> @Dong -- your point about special timestamp values is a very good one.
>>>> The
>>>>> issue may extend to other cases in the protocol where we use
>> timestamps.
>>>> Is
>>>>> this the scope we need to worry about (2 values instead of just 1) or
>> are
>>>>> there others? This also might be something we want to look out for in
>> the
>>>>> future -- using special values relative to <SignedIntType>.MIN_VALUE
>>>>> instead of relative to 0.
>>>>> 
>>>>> -Ewen
>>>>> 
>>>>> On Tue, Dec 12, 2017 at 11:12 AM, Dong Lin <li...@gmail.com>
>> wrote:
>>>>> 
>>>>>> Hey Konstantin,
>>>>>> 
>>>>>> Thanks for updating the KIP.
>>>>>> 
>>>>>> If we were to support negative timestamp in the message, we probably
>>>> also
>>>>>> want to support negative timestamp in ListOffsetRequest. Currently in
>>>>>> ListOffsetRequest, timestamp value -2 is used to indicate earliest
>>>>>> timestamp and timestamp value -1 is used to indicate latest timestamp.
>>>> It
>>>>>> seems that we should make changes accordingly so that -1 and -2 can be
>>>>>> supported as valid timestamp in ListOffsetRequest. What do you think?
>>>>>> 
>>>>>> Thanks,
>>>>>> Dong
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> On Mon, Dec 11, 2017 at 12:55 PM, Konstantin Chukhlomin <
>>>>>> chuhlomin@gmail.com
>>>>>>> wrote:
>>>>>> 
>>>>>>> Hi all,
>>>>>>> 
>>>>>>> I've updated KIP with few more details:
>>>>>>> Added (proposed) Changes in binary message format <
>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-228+
>>>>>>> Negative+record+timestamp+support#KIP-228Negativerecordtimes
>>>>>>> tampsupport-Changesinbinarymessageformat>
>>>>>>> Added Changes from producer perspective <
>> https://cwiki.apache.org/conf
>>>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
>>>>>>> ort#KIP-228Negativerecordtimestampsupport-
>>>> Changesfromproducerperspective
>>>>>>> 
>>>>>>> Added Changes from consumer perspective <
>> https://cwiki.apache.org/conf
>>>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
>>>>>>> ort#KIP-228Negativerecordtimestampsupport-
>>>> Changesfromconsumerperspective
>>>>>>> 
>>>>>>> 
>>>>>>> Let me know if it makes sense to you.
>>>>>>> 
>>>>>>> -Konstantin
>>>>>>> 
>>>>>>>> On Dec 7, 2017, at 2:46 PM, Konstantin Chukhlomin <
>>>> chuhlomin@gmail.com
>>>>>>> 
>>>>>>> wrote:
>>>>>>>> 
>>>>>>>> Hi Matthias,
>>>>>>>> 
>>>>>>>> Indeed for consumers it will be not obvious what −1 means: actual
>>>>>>> timestamp
>>>>>>>> or no timestamp. Nevertheless, it's just −1 millisecond, so I
>> thought
>>>>>> it
>>>>>>> will be
>>>>>>>> not a big deal to leave it (not clean, but acceptable).
>>>>>>>> 
>>>>>>>> I agree that it will much cleaner to have a different type of topics
>>>>>>> that support
>>>>>>>> negative timestamp and/or threat Long.MIN_VALUE as a no-timestamp.
>>>>>>>> I'll update KIP to make it a proposed solution.
>>>>>>>> 
>>>>>>>> Thanks,
>>>>>>>> Konstantin
>>>>>>>> 
>>>>>>>>> On Dec 5, 2017, at 7:06 PM, Matthias J. Sax <matthias@confluent.io
>>> 
>>>>>>> wrote:
>>>>>>>>> 
>>>>>>>>> Thanks for the KIP Konstantin.
>>>>>>>>> 
>>>>>>>>> From my understanding, you propose to just remove the negative
>>>>>> timestamp
>>>>>>>>> check in KafkaProducer and KafkaStreams. If topics are configured
>>>> with
>>>>>>>>> `CreateTime` brokers also write negative timestamps if they are
>>>>>> embedded
>>>>>>>>> in the message.
>>>>>>>>> 
>>>>>>>>> However, I am not sure about the overlapping semantics for -1
>>>>>> timestamp.
>>>>>>>>> My concerns is, that this ambiguity might result in issues. Assume
>>>>>> that
>>>>>>>>> there is a topic (configured with `CreateTime`) for which an old
>> and
>>>> a
>>>>>>>>> new producer are writing. The old producer uses old message format
>>>> and
>>>>>>>>> does not include any timestamp in the message. The broker will
>>>>>> "upgrade"
>>>>>>>>> this message to the new format and set -1. At the same time, the
>> new
>>>>>>>>> producer could write a message with valid timestamp -1. A consumer
>>>>>> could
>>>>>>>>> not distinguish between both cases...
>>>>>>>>> 
>>>>>>>>> Also, there might be other Producer implementations that write
>>>>>> negative
>>>>>>>>> timestamps. Thus, those might already exist. For Streams, we don't
>>>>>>>>> process those and we should make sure to keep it this way (to avoid
>>>>>>>>> ambiguity).
>>>>>>>>> 
>>>>>>>>> Thus, it might actually make sense to introduce a new timestamp
>> type
>>>>>> to
>>>>>>>>> express those new semantics. The question is still, how to deal
>> with
>>>>>>>>> older producer clients that want to write to those topics.
>>>>>>>>> 
>>>>>>>>> - We could either use `Long.MIN_VALUE` as "unknown" (this would be
>>>> way
>>>>>>>>> better than -1 as it's not in the middle of the range but at the
>> very
>>>>>>>>> end and it will also have well-defined semantics).
>>>>>>>>> - Or we use a "mixed-mode" where we use broker wall-clock time for
>>>>>>>>> older message formats (ie, append time semantics for older
>> producers)
>>>>>>>>> - Third, we would even give an error message back to older
>> producers;
>>>>>>>>> this might change the backward compatibility guarantees Kafka
>>>> provides
>>>>>>>>> so far when upgrading brokers. However, this would not affect
>> exiting
>>>>>>>>> topics, but only newly created ones (and we could disallow changing
>>>>>> the
>>>>>>>>> semantics to the new timestamp type to guard against miss
>>>>>>>>> configuration). Thus, it might be ok.
>>>>>>>>> 
>>>>>>>>> For Streams, we could check the topic config and process negative
>>>>>>>>> timestamps only if the topic is configures with the new timestamp
>>>>>> type.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> Maybe I am a little bit to paranoid about overloading -1 semantics.
>>>>>>>>> Curious to get feedback from others.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> -Matthias
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> On 12/5/17 1:24 PM, Konstantin Chukhlomin wrote:
>>>>>>>>>> Hi Dong,
>>>>>>>>>> 
>>>>>>>>>> Currently we are storing historical timestamp in the message.
>>>>>>>>>> 
>>>>>>>>>> What we are trying to achieve is to make it possible to do Kafka
>>>>>> lookup
>>>>>>>>>> by timestamp. Ideally I would do `offsetsForTimes` to find
>> articles
>>>>>>> published
>>>>>>>>>> in 1910s (if we are storing articles on the log).
>>>>>>>>>> 
>>>>>>>>>> So first two suggestions aren't really covering our use-case.
>>>>>>>>>> 
>>>>>>>>>> We could create a new timestamp type like "HistoricalTimestamp" or
>>>>>>> "MaybeNegativeTimestamp".
>>>>>>>>>> And the only difference between this one and CreateTime is that it
>>>>>>> could be negative.
>>>>>>>>>> I tend to use CreateTime for this purpose because it's easier to
>>>>>>> understand from
>>>>>>>>>> user perspective as a timestamp which publisher can set.
>>>>>>>>>> 
>>>>>>>>>> Thanks,
>>>>>>>>>> Konstantin
>>>>>>>>>> 
>>>>>>>>>>> On Dec 5, 2017, at 3:47 PM, Dong Lin <li...@gmail.com>
>> wrote:
>>>>>>>>>>> 
>>>>>>>>>>> Hey Konstantin,
>>>>>>>>>>> 
>>>>>>>>>>> Thanks for the KIP. I have a few questions below.
>>>>>>>>>>> 
>>>>>>>>>>> Strictly speaking Kafka actually allows you to store historical
>>>>>> data.
>>>>>>> And
>>>>>>>>>>> user are free to encode arbitrary timestamp field in their Kafka
>>>>>>> message.
>>>>>>>>>>> For example, your Kafka message can currently have Json or Avro
>>>>>>> format and
>>>>>>>>>>> you can put a timestamp field there. Do you think that could
>>>> address
>>>>>>> your
>>>>>>>>>>> use-case?
>>>>>>>>>>> 
>>>>>>>>>>> Alternatively, KIP-82 introduced Record Header in Kafka and you
>> can
>>>>>>> also
>>>>>>>>>>> define your customized key/value pair in the header. Do you think
>>>>>>> this can
>>>>>>>>>>> address your use-case?
>>>>>>>>>>> 
>>>>>>>>>>> Also, currently there are two types of timestamp according to
>>>>>> KIP-32.
>>>>>>> If
>>>>>>>>>>> the type is LogAppendTime then the timestamp value is the time
>> when
>>>>>>> broker
>>>>>>>>>>> receives the message. If the type is CreateTime then the
>> timestamp
>>>>>>> value is
>>>>>>>>>>> determined when producer produces message. With these two
>>>>>>> definitions, the
>>>>>>>>>>> timestamp should always be positive. We probably need a new type
>>>>>> here
>>>>>>> if we
>>>>>>>>>>> can not put timestamp in the Record Header or the message
>> payload.
>>>>>>> Does
>>>>>>>>>>> this sound reasonable?
>>>>>>>>>>> 
>>>>>>>>>>> Thanks,
>>>>>>>>>>> Dong
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> On Tue, Dec 5, 2017 at 8:40 AM, Konstantin Chukhlomin <
>>>>>>> chuhlomin@gmail.com>
>>>>>>>>>>> wrote:
>>>>>>>>>>> 
>>>>>>>>>>>> Hi all,
>>>>>>>>>>>> 
>>>>>>>>>>>> I have created a KIP to support negative timestamp:
>>>>>>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
>>>>>>>>>>>> 228+Negative+record+timestamp+support <
>> https://cwiki.apache.org/
>>>>>>>>>>>> confluence/display/KAFKA/KIP-228+Negative+record+timestamp+
>>>>>> support>
>>>>>>>>>>>> 
>>>>>>>>>>>> Here are proposed changes: https://github.com/apache/
>>>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk <
>> https://github.com/apache/
>>>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk>
>>>>>>>>>>>> 
>>>>>>>>>>>> I'm pretty sure that not cases are covered, so comments and
>>>>>>> suggestions
>>>>>>>>>>>> are welcome.
>>>>>>>>>>>> 
>>>>>>>>>>>> Thank you,
>>>>>>>>>>>> Konstantin
>>>>>>>>>> 
>>>>>>>>> 
>>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>>> 
>>>> 
>>>> 
>>> 
>> 
>> 

Re: [DISCUSS] KIP-228 Negative record timestamp support

[Ewen Cheslack-Postava <ew...@confluent.io>]

On Tue, Jan 2, 2018 at 8:04 PM, Matthias J. Sax <ma...@confluent.io>
wrote:

> I was thinking about a broker/topic config.
>
> However, I am not sure if we only need to worry about data written in
> the future (this would only be true, if there would be no records with
> -1 timestamp already). Assume that we you an existing topic that
> contains data with -1 = UNKNOWN records -- for this case, we would give
> those timestamps a new semantics if we suddenly allow negative
> timestamps. (Assuming that we don't allow -1 as a gap in the timeline
> what I would rather not do.)
>

Using the Java producer you cannot have a negative timestamp today. So
(modulo comment about being dependent on the client implementation), no
existing data should have -1 timestamp unless it is NO_TIMESTAMP.

When you say you'd rather not like to have -1 as a gap in the timeline, can
you explain the potential scale of impact? I view it as a relatively
unlikely value and something that people who are really concerned with
negative timestamps can easily work around. Probably many users won't care
as they will not be using pre-1970s data where they actually set the Kafka
timestamp (rather than having timestamps embedded in the data) anyway. I
agree it isn't ideal, but to me it looks like a reasonable tradeoff. What
are the effects/use cases that make you concerned that we'd see significant
user pain as a result?


>
> Also note, that it's not really client specific IMHO, as one could
> implement their own clients. There are many third party clients and we
> don't know if they check for negative timestamps (applications could
> even assign their own special meaning to negative timestamps as those
> are unused atm) -- furthermore, all older client not embedding a
> timestamp default to -1 on the broker side...
>

I said "client-specific" because some of the checks are done on the
client-side, which means they are dependent on the specific client
implementation being used. Based on the rest of your comment, I think we're
in agreement except for how we are naming things :) I'd have to double
check if the same level of enforcement is done broker-side. I only mention
that because we tend to discuss these proposals in the context of only the
Java clients, but it is worth thinking through the impact to other clients
as well.


>
> > The implementation could easily be made to map
> > those values into a range that is less likely to be utilized (e.g. use
> the
> > values near Long.MIN_VALUE and have the consumer convert back as needed).
> > The sentinel for NO_TIMESTAMP could be changed between versions as long
> as
> > it is handled consistently between client versions.
>
> This opens Pandora's box IMHO.
>

Why? There should be a small number of values that need to be mapped and
someone could think through the different compatibility issues that are
possible to determine if there are any significant issues/drawbacks.


>
> > Introducing the new
> > config seems like it has significant compatibility concerns that need to
> be
> > sorted out.
>
> I cannot follow here -- from my point of view, it relaxes compatibility
> concerns. If we only allow new topic to enable negative timestamps, old
> behavior and new behavior are not mixed. IMHO, mixing both would be a
> real issue. Thus, for new topics we can change "unknown" from -1 to
> Long.MIN_VALUE and don't mix two different approaches within a single
> topic.
>

What's the mechanism for this? Is the new config only allowed in
CreateTopics requests? If you use existing tooling to set topic configs,
you would just be able to set any valid config. Are the semantics just
undefined if you do? Unless it is impossible to do certain things, we have
to deal with the compatibility concerns regardless of intended use. Might
be fine to just say the behavior is undefined, but there's still work to be
done there. Regardless, I didn't (and probably still don't) have a concrete
understanding of the proposed setting, so hard for me to reason about it.

-Ewen


>
> I see your point that we do have too many configs -- we could also make
> it a new value for existing `message.timestamp.type`.
>
>
> -Matthias
>
>
> On 1/2/18 7:48 PM, Ewen Cheslack-Postava wrote:
> > For `allow.negative.timestamps`, do you mean this as a broker config? I'm
> > not entirely clear on what the proposal would entail.
> >
> > I think taking into account whether we're talking about compatibility
> with
> > existing data in Kafka vs enabling use of negative timestamps is
> important
> > here. If they're effectively not supported today (though admittedly this
> is
> > really client-specific), then we need only concern ourselves with data
> that
> > hasn't been produced into Kafka yet. In that case, we can always handle
> > sentinel values in special ways if we really want to. For example, the
> Java
> > producer does not accept any values < 0 and the API supports passing null
> > rather than the sentinels. The implementation could easily be made to map
> > those values into a range that is less likely to be utilized (e.g. use
> the
> > values near Long.MIN_VALUE and have the consumer convert back as needed).
> > The sentinel for NO_TIMESTAMP could be changed between versions as long
> as
> > it is handled consistently between client versions.
> >
> > IMO we already have way too many configs, so we should think about where
> > the impact is and if a not ideal, but also not significant compromise can
> > be made and avoid most of the additional complexity. Introducing the new
> > config seems like it has significant compatibility concerns that need to
> be
> > sorted out. In contrast, I suspect the use cases we need to support that
> > have come up so far can handle 1 or 2 special cases and the necessary
> > munging could be handled safely by interceptors such that it is trivial
> to
> > make sure all your apps do the right thing. I appreciate the pain of a
> ton
> > of mailing list questions about an issue like this, but given the
> > likelihood of encountering that particular value, I just find it unlikely
> > it would be that common and I think it's a reasonable tradeoff to tell a
> > user they might need to handle that one special case.
> >
> > -Ewen
> >
> > On Thu, Dec 28, 2017 at 12:58 PM, Matthias J. Sax <matthias@confluent.io
> >
> > wrote:
> >
> >> I agree that changing message format or using a flag bit might not be
> >> worth it.
> >>
> >> However, just keeping -1 as "unknown" leaving a time gap give me a lot
> >> of headache, too. Your arguments about "not an issue in practice" kinda
> >> make sense to me, but I see the number of question on the mailing list
> >> already if we really follow this path... It will confuse users that
> >> don't pay attention and "loose" data if Kafka Streams drops records with
> >> timestamp -1 but processes other records with negative timestamps.
> >>
> >> Thus, I was wondering if a new topic config (maybe
> >> `allow.negative.timestamps` with default `false`) that allows for enable
> >> negative timestamps would be the better solution? With this new config,
> >> we would not have any sentinel value for "unknown" and all timestamps
> >> would be valid. Old producers, can't write to those topics if they are
> >> configured with CREATE_TIME though; APPEND_TIME would still work for
> >> older producers but with APPEND_TIME no negative timestamps are possible
> >> in the first place, so this config would not have any impact anyway.
> >>
> >> Kafka Streams could check the topic config and only drop negative
> >> timestamps is they are not enabled. Or course, existing topic should not
> >> enable negative timestamps if there are records with -1 in them already
> >> -- otherwise, semantics break down -- but this would be a config error
> >> we cannot prevent. However, I would expect that mostly newly created
> >> topics would enable this config anyway.
> >>
> >>
> >> -Matthias
> >>
> >> On 12/18/17 10:47 PM, Ewen Cheslack-Postava wrote:
> >>> I think the trivial change of just recognizing using -1 was a mistake
> >> for a
> >>> sentinel value and special casing it while allowing other negative
> values
> >>> through is the most practical, reasonable change.
> >>>
> >>> Realistically, the scope of impact for that -1 is pretty tiny, as has
> >> been
> >>> pointed out. A single millisecond gap in available timestamps in 1969.
> >> For
> >>> producers that really want to be careful (as the NYT data might want to
> >>> be), having the producer layer adjust accordingly is unlikely to be an
> >>> issue (you can't assume these timestamps are unique anyway, so they
> >> cannot
> >>> reasonably used for ordering; adjusting by 1ms is a practical
> tradeoff).
> >>>
> >>> Other approaches where we modify the semantics of the timestamp from
> the
> >>> two existing modes require eating up valuable flags in the message
> >> format,
> >>> or ramping the message format version, all of which make things
> >>> significantly messier. Hell, timezones, leap seconds, and ms
> granularity
> >>> probably make that 1ms window pretty much moot for any practical
> >>> applications, and for the extremely rare case that an application might
> >>> care, they are probably willing to pay the cost of a secondary index if
> >>> they needed to store timestamp values in the payload rather than in the
> >>> metadata.
> >>>
> >>> Given that we have the current system in place, I suspect that any
> >>> translation to using Long.MIN_VALUE as the sentinel is probably just
> more
> >>> confusing to users, adds more implementation overhead to client
> >> libraries,
> >>> and is more likely to introduce bugs.
> >>>
> >>> Warts like these always feel wrong when approached from pure design
> >>> principles, but the fact is that the constraints are already there. To
> >> me,
> >>> none of the proposals to move to an encoding we'd prefer seem to add
> >> enough
> >>> value to outweigh the migration, compatibility, and implementation
> costs.
> >>>
> >>> @Dong -- your point about special timestamp values is a very good one.
> >> The
> >>> issue may extend to other cases in the protocol where we use
> timestamps.
> >> Is
> >>> this the scope we need to worry about (2 values instead of just 1) or
> are
> >>> there others? This also might be something we want to look out for in
> the
> >>> future -- using special values relative to <SignedIntType>.MIN_VALUE
> >>> instead of relative to 0.
> >>>
> >>> -Ewen
> >>>
> >>> On Tue, Dec 12, 2017 at 11:12 AM, Dong Lin <li...@gmail.com>
> wrote:
> >>>
> >>>> Hey Konstantin,
> >>>>
> >>>> Thanks for updating the KIP.
> >>>>
> >>>> If we were to support negative timestamp in the message, we probably
> >> also
> >>>> want to support negative timestamp in ListOffsetRequest. Currently in
> >>>> ListOffsetRequest, timestamp value -2 is used to indicate earliest
> >>>> timestamp and timestamp value -1 is used to indicate latest timestamp.
> >> It
> >>>> seems that we should make changes accordingly so that -1 and -2 can be
> >>>> supported as valid timestamp in ListOffsetRequest. What do you think?
> >>>>
> >>>> Thanks,
> >>>> Dong
> >>>>
> >>>>
> >>>>
> >>>> On Mon, Dec 11, 2017 at 12:55 PM, Konstantin Chukhlomin <
> >>>> chuhlomin@gmail.com
> >>>>> wrote:
> >>>>
> >>>>> Hi all,
> >>>>>
> >>>>> I've updated KIP with few more details:
> >>>>> Added (proposed) Changes in binary message format <
> >>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-228+
> >>>>> Negative+record+timestamp+support#KIP-228Negativerecordtimes
> >>>>> tampsupport-Changesinbinarymessageformat>
> >>>>> Added Changes from producer perspective <
> https://cwiki.apache.org/conf
> >>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> >>>>> ort#KIP-228Negativerecordtimestampsupport-
> >> Changesfromproducerperspective
> >>>>>
> >>>>> Added Changes from consumer perspective <
> https://cwiki.apache.org/conf
> >>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
> >>>>> ort#KIP-228Negativerecordtimestampsupport-
> >> Changesfromconsumerperspective
> >>>>>
> >>>>>
> >>>>> Let me know if it makes sense to you.
> >>>>>
> >>>>> -Konstantin
> >>>>>
> >>>>>> On Dec 7, 2017, at 2:46 PM, Konstantin Chukhlomin <
> >> chuhlomin@gmail.com
> >>>>>
> >>>>> wrote:
> >>>>>>
> >>>>>> Hi Matthias,
> >>>>>>
> >>>>>> Indeed for consumers it will be not obvious what −1 means: actual
> >>>>> timestamp
> >>>>>> or no timestamp. Nevertheless, it's just −1 millisecond, so I
> thought
> >>>> it
> >>>>> will be
> >>>>>> not a big deal to leave it (not clean, but acceptable).
> >>>>>>
> >>>>>> I agree that it will much cleaner to have a different type of topics
> >>>>> that support
> >>>>>> negative timestamp and/or threat Long.MIN_VALUE as a no-timestamp.
> >>>>>> I'll update KIP to make it a proposed solution.
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Konstantin
> >>>>>>
> >>>>>>> On Dec 5, 2017, at 7:06 PM, Matthias J. Sax <matthias@confluent.io
> >
> >>>>> wrote:
> >>>>>>>
> >>>>>>> Thanks for the KIP Konstantin.
> >>>>>>>
> >>>>>>> From my understanding, you propose to just remove the negative
> >>>> timestamp
> >>>>>>> check in KafkaProducer and KafkaStreams. If topics are configured
> >> with
> >>>>>>> `CreateTime` brokers also write negative timestamps if they are
> >>>> embedded
> >>>>>>> in the message.
> >>>>>>>
> >>>>>>> However, I am not sure about the overlapping semantics for -1
> >>>> timestamp.
> >>>>>>> My concerns is, that this ambiguity might result in issues. Assume
> >>>> that
> >>>>>>> there is a topic (configured with `CreateTime`) for which an old
> and
> >> a
> >>>>>>> new producer are writing. The old producer uses old message format
> >> and
> >>>>>>> does not include any timestamp in the message. The broker will
> >>>> "upgrade"
> >>>>>>> this message to the new format and set -1. At the same time, the
> new
> >>>>>>> producer could write a message with valid timestamp -1. A consumer
> >>>> could
> >>>>>>> not distinguish between both cases...
> >>>>>>>
> >>>>>>> Also, there might be other Producer implementations that write
> >>>> negative
> >>>>>>> timestamps. Thus, those might already exist. For Streams, we don't
> >>>>>>> process those and we should make sure to keep it this way (to avoid
> >>>>>>> ambiguity).
> >>>>>>>
> >>>>>>> Thus, it might actually make sense to introduce a new timestamp
> type
> >>>> to
> >>>>>>> express those new semantics. The question is still, how to deal
> with
> >>>>>>> older producer clients that want to write to those topics.
> >>>>>>>
> >>>>>>> - We could either use `Long.MIN_VALUE` as "unknown" (this would be
> >> way
> >>>>>>> better than -1 as it's not in the middle of the range but at the
> very
> >>>>>>> end and it will also have well-defined semantics).
> >>>>>>> - Or we use a "mixed-mode" where we use broker wall-clock time for
> >>>>>>> older message formats (ie, append time semantics for older
> producers)
> >>>>>>> - Third, we would even give an error message back to older
> producers;
> >>>>>>> this might change the backward compatibility guarantees Kafka
> >> provides
> >>>>>>> so far when upgrading brokers. However, this would not affect
> exiting
> >>>>>>> topics, but only newly created ones (and we could disallow changing
> >>>> the
> >>>>>>> semantics to the new timestamp type to guard against miss
> >>>>>>> configuration). Thus, it might be ok.
> >>>>>>>
> >>>>>>> For Streams, we could check the topic config and process negative
> >>>>>>> timestamps only if the topic is configures with the new timestamp
> >>>> type.
> >>>>>>>
> >>>>>>>
> >>>>>>> Maybe I am a little bit to paranoid about overloading -1 semantics.
> >>>>>>> Curious to get feedback from others.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> -Matthias
> >>>>>>>
> >>>>>>>
> >>>>>>> On 12/5/17 1:24 PM, Konstantin Chukhlomin wrote:
> >>>>>>>> Hi Dong,
> >>>>>>>>
> >>>>>>>> Currently we are storing historical timestamp in the message.
> >>>>>>>>
> >>>>>>>> What we are trying to achieve is to make it possible to do Kafka
> >>>> lookup
> >>>>>>>> by timestamp. Ideally I would do `offsetsForTimes` to find
> articles
> >>>>> published
> >>>>>>>> in 1910s (if we are storing articles on the log).
> >>>>>>>>
> >>>>>>>> So first two suggestions aren't really covering our use-case.
> >>>>>>>>
> >>>>>>>> We could create a new timestamp type like "HistoricalTimestamp" or
> >>>>> "MaybeNegativeTimestamp".
> >>>>>>>> And the only difference between this one and CreateTime is that it
> >>>>> could be negative.
> >>>>>>>> I tend to use CreateTime for this purpose because it's easier to
> >>>>> understand from
> >>>>>>>> user perspective as a timestamp which publisher can set.
> >>>>>>>>
> >>>>>>>> Thanks,
> >>>>>>>> Konstantin
> >>>>>>>>
> >>>>>>>>> On Dec 5, 2017, at 3:47 PM, Dong Lin <li...@gmail.com>
> wrote:
> >>>>>>>>>
> >>>>>>>>> Hey Konstantin,
> >>>>>>>>>
> >>>>>>>>> Thanks for the KIP. I have a few questions below.
> >>>>>>>>>
> >>>>>>>>> Strictly speaking Kafka actually allows you to store historical
> >>>> data.
> >>>>> And
> >>>>>>>>> user are free to encode arbitrary timestamp field in their Kafka
> >>>>> message.
> >>>>>>>>> For example, your Kafka message can currently have Json or Avro
> >>>>> format and
> >>>>>>>>> you can put a timestamp field there. Do you think that could
> >> address
> >>>>> your
> >>>>>>>>> use-case?
> >>>>>>>>>
> >>>>>>>>> Alternatively, KIP-82 introduced Record Header in Kafka and you
> can
> >>>>> also
> >>>>>>>>> define your customized key/value pair in the header. Do you think
> >>>>> this can
> >>>>>>>>> address your use-case?
> >>>>>>>>>
> >>>>>>>>> Also, currently there are two types of timestamp according to
> >>>> KIP-32.
> >>>>> If
> >>>>>>>>> the type is LogAppendTime then the timestamp value is the time
> when
> >>>>> broker
> >>>>>>>>> receives the message. If the type is CreateTime then the
> timestamp
> >>>>> value is
> >>>>>>>>> determined when producer produces message. With these two
> >>>>> definitions, the
> >>>>>>>>> timestamp should always be positive. We probably need a new type
> >>>> here
> >>>>> if we
> >>>>>>>>> can not put timestamp in the Record Header or the message
> payload.
> >>>>> Does
> >>>>>>>>> this sound reasonable?
> >>>>>>>>>
> >>>>>>>>> Thanks,
> >>>>>>>>> Dong
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On Tue, Dec 5, 2017 at 8:40 AM, Konstantin Chukhlomin <
> >>>>> chuhlomin@gmail.com>
> >>>>>>>>> wrote:
> >>>>>>>>>
> >>>>>>>>>> Hi all,
> >>>>>>>>>>
> >>>>>>>>>> I have created a KIP to support negative timestamp:
> >>>>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> >>>>>>>>>> 228+Negative+record+timestamp+support <
> https://cwiki.apache.org/
> >>>>>>>>>> confluence/display/KAFKA/KIP-228+Negative+record+timestamp+
> >>>> support>
> >>>>>>>>>>
> >>>>>>>>>> Here are proposed changes: https://github.com/apache/
> >>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk <
> https://github.com/apache/
> >>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk>
> >>>>>>>>>>
> >>>>>>>>>> I'm pretty sure that not cases are covered, so comments and
> >>>>> suggestions
> >>>>>>>>>> are welcome.
> >>>>>>>>>>
> >>>>>>>>>> Thank you,
> >>>>>>>>>> Konstantin
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>>
> >>>>
> >>>
> >>
> >>
> >
>
>

Re: [DISCUSS] KIP-228 Negative record timestamp support

["Matthias J. Sax" <ma...@confluent.io>]

I was thinking about a broker/topic config.

However, I am not sure if we only need to worry about data written in
the future (this would only be true, if there would be no records with
-1 timestamp already). Assume that we you an existing topic that
contains data with -1 = UNKNOWN records -- for this case, we would give
those timestamps a new semantics if we suddenly allow negative
timestamps. (Assuming that we don't allow -1 as a gap in the timeline
what I would rather not do.)

Also note, that it's not really client specific IMHO, as one could
implement their own clients. There are many third party clients and we
don't know if they check for negative timestamps (applications could
even assign their own special meaning to negative timestamps as those
are unused atm) -- furthermore, all older client not embedding a
timestamp default to -1 on the broker side...

> The implementation could easily be made to map
> those values into a range that is less likely to be utilized (e.g. use the
> values near Long.MIN_VALUE and have the consumer convert back as needed).
> The sentinel for NO_TIMESTAMP could be changed between versions as long as
> it is handled consistently between client versions.

This opens Pandora's box IMHO.

> Introducing the new
> config seems like it has significant compatibility concerns that need to be
> sorted out. 

I cannot follow here -- from my point of view, it relaxes compatibility
concerns. If we only allow new topic to enable negative timestamps, old
behavior and new behavior are not mixed. IMHO, mixing both would be a
real issue. Thus, for new topics we can change "unknown" from -1 to
Long.MIN_VALUE and don't mix two different approaches within a single topic.

I see your point that we do have too many configs -- we could also make
it a new value for existing `message.timestamp.type`.


-Matthias


On 1/2/18 7:48 PM, Ewen Cheslack-Postava wrote:
> For `allow.negative.timestamps`, do you mean this as a broker config? I'm
> not entirely clear on what the proposal would entail.
> 
> I think taking into account whether we're talking about compatibility with
> existing data in Kafka vs enabling use of negative timestamps is important
> here. If they're effectively not supported today (though admittedly this is
> really client-specific), then we need only concern ourselves with data that
> hasn't been produced into Kafka yet. In that case, we can always handle
> sentinel values in special ways if we really want to. For example, the Java
> producer does not accept any values < 0 and the API supports passing null
> rather than the sentinels. The implementation could easily be made to map
> those values into a range that is less likely to be utilized (e.g. use the
> values near Long.MIN_VALUE and have the consumer convert back as needed).
> The sentinel for NO_TIMESTAMP could be changed between versions as long as
> it is handled consistently between client versions.
> 
> IMO we already have way too many configs, so we should think about where
> the impact is and if a not ideal, but also not significant compromise can
> be made and avoid most of the additional complexity. Introducing the new
> config seems like it has significant compatibility concerns that need to be
> sorted out. In contrast, I suspect the use cases we need to support that
> have come up so far can handle 1 or 2 special cases and the necessary
> munging could be handled safely by interceptors such that it is trivial to
> make sure all your apps do the right thing. I appreciate the pain of a ton
> of mailing list questions about an issue like this, but given the
> likelihood of encountering that particular value, I just find it unlikely
> it would be that common and I think it's a reasonable tradeoff to tell a
> user they might need to handle that one special case.
> 
> -Ewen
> 
> On Thu, Dec 28, 2017 at 12:58 PM, Matthias J. Sax <ma...@confluent.io>
> wrote:
> 
>> I agree that changing message format or using a flag bit might not be
>> worth it.
>>
>> However, just keeping -1 as "unknown" leaving a time gap give me a lot
>> of headache, too. Your arguments about "not an issue in practice" kinda
>> make sense to me, but I see the number of question on the mailing list
>> already if we really follow this path... It will confuse users that
>> don't pay attention and "loose" data if Kafka Streams drops records with
>> timestamp -1 but processes other records with negative timestamps.
>>
>> Thus, I was wondering if a new topic config (maybe
>> `allow.negative.timestamps` with default `false`) that allows for enable
>> negative timestamps would be the better solution? With this new config,
>> we would not have any sentinel value for "unknown" and all timestamps
>> would be valid. Old producers, can't write to those topics if they are
>> configured with CREATE_TIME though; APPEND_TIME would still work for
>> older producers but with APPEND_TIME no negative timestamps are possible
>> in the first place, so this config would not have any impact anyway.
>>
>> Kafka Streams could check the topic config and only drop negative
>> timestamps is they are not enabled. Or course, existing topic should not
>> enable negative timestamps if there are records with -1 in them already
>> -- otherwise, semantics break down -- but this would be a config error
>> we cannot prevent. However, I would expect that mostly newly created
>> topics would enable this config anyway.
>>
>>
>> -Matthias
>>
>> On 12/18/17 10:47 PM, Ewen Cheslack-Postava wrote:
>>> I think the trivial change of just recognizing using -1 was a mistake
>> for a
>>> sentinel value and special casing it while allowing other negative values
>>> through is the most practical, reasonable change.
>>>
>>> Realistically, the scope of impact for that -1 is pretty tiny, as has
>> been
>>> pointed out. A single millisecond gap in available timestamps in 1969.
>> For
>>> producers that really want to be careful (as the NYT data might want to
>>> be), having the producer layer adjust accordingly is unlikely to be an
>>> issue (you can't assume these timestamps are unique anyway, so they
>> cannot
>>> reasonably used for ordering; adjusting by 1ms is a practical tradeoff).
>>>
>>> Other approaches where we modify the semantics of the timestamp from the
>>> two existing modes require eating up valuable flags in the message
>> format,
>>> or ramping the message format version, all of which make things
>>> significantly messier. Hell, timezones, leap seconds, and ms granularity
>>> probably make that 1ms window pretty much moot for any practical
>>> applications, and for the extremely rare case that an application might
>>> care, they are probably willing to pay the cost of a secondary index if
>>> they needed to store timestamp values in the payload rather than in the
>>> metadata.
>>>
>>> Given that we have the current system in place, I suspect that any
>>> translation to using Long.MIN_VALUE as the sentinel is probably just more
>>> confusing to users, adds more implementation overhead to client
>> libraries,
>>> and is more likely to introduce bugs.
>>>
>>> Warts like these always feel wrong when approached from pure design
>>> principles, but the fact is that the constraints are already there. To
>> me,
>>> none of the proposals to move to an encoding we'd prefer seem to add
>> enough
>>> value to outweigh the migration, compatibility, and implementation costs.
>>>
>>> @Dong -- your point about special timestamp values is a very good one.
>> The
>>> issue may extend to other cases in the protocol where we use timestamps.
>> Is
>>> this the scope we need to worry about (2 values instead of just 1) or are
>>> there others? This also might be something we want to look out for in the
>>> future -- using special values relative to <SignedIntType>.MIN_VALUE
>>> instead of relative to 0.
>>>
>>> -Ewen
>>>
>>> On Tue, Dec 12, 2017 at 11:12 AM, Dong Lin <li...@gmail.com> wrote:
>>>
>>>> Hey Konstantin,
>>>>
>>>> Thanks for updating the KIP.
>>>>
>>>> If we were to support negative timestamp in the message, we probably
>> also
>>>> want to support negative timestamp in ListOffsetRequest. Currently in
>>>> ListOffsetRequest, timestamp value -2 is used to indicate earliest
>>>> timestamp and timestamp value -1 is used to indicate latest timestamp.
>> It
>>>> seems that we should make changes accordingly so that -1 and -2 can be
>>>> supported as valid timestamp in ListOffsetRequest. What do you think?
>>>>
>>>> Thanks,
>>>> Dong
>>>>
>>>>
>>>>
>>>> On Mon, Dec 11, 2017 at 12:55 PM, Konstantin Chukhlomin <
>>>> chuhlomin@gmail.com
>>>>> wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I've updated KIP with few more details:
>>>>> Added (proposed) Changes in binary message format <
>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-228+
>>>>> Negative+record+timestamp+support#KIP-228Negativerecordtimes
>>>>> tampsupport-Changesinbinarymessageformat>
>>>>> Added Changes from producer perspective <https://cwiki.apache.org/conf
>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
>>>>> ort#KIP-228Negativerecordtimestampsupport-
>> Changesfromproducerperspective
>>>>>
>>>>> Added Changes from consumer perspective <https://cwiki.apache.org/conf
>>>>> luence/display/KAFKA/KIP-228+Negative+record+timestamp+supp
>>>>> ort#KIP-228Negativerecordtimestampsupport-
>> Changesfromconsumerperspective
>>>>>
>>>>>
>>>>> Let me know if it makes sense to you.
>>>>>
>>>>> -Konstantin
>>>>>
>>>>>> On Dec 7, 2017, at 2:46 PM, Konstantin Chukhlomin <
>> chuhlomin@gmail.com
>>>>>
>>>>> wrote:
>>>>>>
>>>>>> Hi Matthias,
>>>>>>
>>>>>> Indeed for consumers it will be not obvious what −1 means: actual
>>>>> timestamp
>>>>>> or no timestamp. Nevertheless, it's just −1 millisecond, so I thought
>>>> it
>>>>> will be
>>>>>> not a big deal to leave it (not clean, but acceptable).
>>>>>>
>>>>>> I agree that it will much cleaner to have a different type of topics
>>>>> that support
>>>>>> negative timestamp and/or threat Long.MIN_VALUE as a no-timestamp.
>>>>>> I'll update KIP to make it a proposed solution.
>>>>>>
>>>>>> Thanks,
>>>>>> Konstantin
>>>>>>
>>>>>>> On Dec 5, 2017, at 7:06 PM, Matthias J. Sax <ma...@confluent.io>
>>>>> wrote:
>>>>>>>
>>>>>>> Thanks for the KIP Konstantin.
>>>>>>>
>>>>>>> From my understanding, you propose to just remove the negative
>>>> timestamp
>>>>>>> check in KafkaProducer and KafkaStreams. If topics are configured
>> with
>>>>>>> `CreateTime` brokers also write negative timestamps if they are
>>>> embedded
>>>>>>> in the message.
>>>>>>>
>>>>>>> However, I am not sure about the overlapping semantics for -1
>>>> timestamp.
>>>>>>> My concerns is, that this ambiguity might result in issues. Assume
>>>> that
>>>>>>> there is a topic (configured with `CreateTime`) for which an old and
>> a
>>>>>>> new producer are writing. The old producer uses old message format
>> and
>>>>>>> does not include any timestamp in the message. The broker will
>>>> "upgrade"
>>>>>>> this message to the new format and set -1. At the same time, the new
>>>>>>> producer could write a message with valid timestamp -1. A consumer
>>>> could
>>>>>>> not distinguish between both cases...
>>>>>>>
>>>>>>> Also, there might be other Producer implementations that write
>>>> negative
>>>>>>> timestamps. Thus, those might already exist. For Streams, we don't
>>>>>>> process those and we should make sure to keep it this way (to avoid
>>>>>>> ambiguity).
>>>>>>>
>>>>>>> Thus, it might actually make sense to introduce a new timestamp type
>>>> to
>>>>>>> express those new semantics. The question is still, how to deal with
>>>>>>> older producer clients that want to write to those topics.
>>>>>>>
>>>>>>> - We could either use `Long.MIN_VALUE` as "unknown" (this would be
>> way
>>>>>>> better than -1 as it's not in the middle of the range but at the very
>>>>>>> end and it will also have well-defined semantics).
>>>>>>> - Or we use a "mixed-mode" where we use broker wall-clock time for
>>>>>>> older message formats (ie, append time semantics for older producers)
>>>>>>> - Third, we would even give an error message back to older producers;
>>>>>>> this might change the backward compatibility guarantees Kafka
>> provides
>>>>>>> so far when upgrading brokers. However, this would not affect exiting
>>>>>>> topics, but only newly created ones (and we could disallow changing
>>>> the
>>>>>>> semantics to the new timestamp type to guard against miss
>>>>>>> configuration). Thus, it might be ok.
>>>>>>>
>>>>>>> For Streams, we could check the topic config and process negative
>>>>>>> timestamps only if the topic is configures with the new timestamp
>>>> type.
>>>>>>>
>>>>>>>
>>>>>>> Maybe I am a little bit to paranoid about overloading -1 semantics.
>>>>>>> Curious to get feedback from others.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> -Matthias
>>>>>>>
>>>>>>>
>>>>>>> On 12/5/17 1:24 PM, Konstantin Chukhlomin wrote:
>>>>>>>> Hi Dong,
>>>>>>>>
>>>>>>>> Currently we are storing historical timestamp in the message.
>>>>>>>>
>>>>>>>> What we are trying to achieve is to make it possible to do Kafka
>>>> lookup
>>>>>>>> by timestamp. Ideally I would do `offsetsForTimes` to find articles
>>>>> published
>>>>>>>> in 1910s (if we are storing articles on the log).
>>>>>>>>
>>>>>>>> So first two suggestions aren't really covering our use-case.
>>>>>>>>
>>>>>>>> We could create a new timestamp type like "HistoricalTimestamp" or
>>>>> "MaybeNegativeTimestamp".
>>>>>>>> And the only difference between this one and CreateTime is that it
>>>>> could be negative.
>>>>>>>> I tend to use CreateTime for this purpose because it's easier to
>>>>> understand from
>>>>>>>> user perspective as a timestamp which publisher can set.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Konstantin
>>>>>>>>
>>>>>>>>> On Dec 5, 2017, at 3:47 PM, Dong Lin <li...@gmail.com> wrote:
>>>>>>>>>
>>>>>>>>> Hey Konstantin,
>>>>>>>>>
>>>>>>>>> Thanks for the KIP. I have a few questions below.
>>>>>>>>>
>>>>>>>>> Strictly speaking Kafka actually allows you to store historical
>>>> data.
>>>>> And
>>>>>>>>> user are free to encode arbitrary timestamp field in their Kafka
>>>>> message.
>>>>>>>>> For example, your Kafka message can currently have Json or Avro
>>>>> format and
>>>>>>>>> you can put a timestamp field there. Do you think that could
>> address
>>>>> your
>>>>>>>>> use-case?
>>>>>>>>>
>>>>>>>>> Alternatively, KIP-82 introduced Record Header in Kafka and you can
>>>>> also
>>>>>>>>> define your customized key/value pair in the header. Do you think
>>>>> this can
>>>>>>>>> address your use-case?
>>>>>>>>>
>>>>>>>>> Also, currently there are two types of timestamp according to
>>>> KIP-32.
>>>>> If
>>>>>>>>> the type is LogAppendTime then the timestamp value is the time when
>>>>> broker
>>>>>>>>> receives the message. If the type is CreateTime then the timestamp
>>>>> value is
>>>>>>>>> determined when producer produces message. With these two
>>>>> definitions, the
>>>>>>>>> timestamp should always be positive. We probably need a new type
>>>> here
>>>>> if we
>>>>>>>>> can not put timestamp in the Record Header or the message payload.
>>>>> Does
>>>>>>>>> this sound reasonable?
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Dong
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Tue, Dec 5, 2017 at 8:40 AM, Konstantin Chukhlomin <
>>>>> chuhlomin@gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Hi all,
>>>>>>>>>>
>>>>>>>>>> I have created a KIP to support negative timestamp:
>>>>>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
>>>>>>>>>> 228+Negative+record+timestamp+support <https://cwiki.apache.org/
>>>>>>>>>> confluence/display/KAFKA/KIP-228+Negative+record+timestamp+
>>>> support>
>>>>>>>>>>
>>>>>>>>>> Here are proposed changes: https://github.com/apache/
>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk <https://github.com/apache/
>>>>>>>>>> kafka/compare/trunk...chuhlomin:trunk>
>>>>>>>>>>
>>>>>>>>>> I'm pretty sure that not cases are covered, so comments and
>>>>> suggestions
>>>>>>>>>> are welcome.
>>>>>>>>>>
>>>>>>>>>> Thank you,
>>>>>>>>>> Konstantin
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>>
>