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Posted to users@kafka.apache.org by Pushkar Deole <pd...@gmail.com> on 2020/04/29 10:08:55 UTC
are kafka state stores global or local?
Hi,
I am looking for some information as to whether kafka state store
KeyValueStore is global or local only. I found that it can be in-memory or
made persistent which stores it in local Rocksdb and also logging can be
enabled so the state is backed by a topic which allows the state store to
be fault tolerant.
However the information that I am looking for is: whether the state store
can be global i.e. if the state written by one application is available to
the other application in real time even when both the applications are
running i.e. no rebalancing has triggered?
Re: are kafka state stores global or local?
Posted by "Matthias J. Sax" <mj...@apache.org>.
That is correct.
For global stores, in fact you cannot put "arbitrary" data into the
store. The `Processor` should _only_ take the input data from the topic,
and put it into the store without modification.
(cf. https://issues.apache.org/jira/browse/KAFKA-7663)
If you want to update all copies of the global store, you need to write
into the global store's input topic: for this case, all instances would
pick up the data and update their local replica.
-Matthias
On 4/30/20 12:39 AM, Pushkar Deole wrote:
> Thanks Matthias !
>
> my question (So, does it mean that the state store modified locally by each
> application is replicated to all other applications) was mainly about
> "global state store",
> As I understand it from your previous response, the state for global state
> store would be replicated to all instances, please correct me if wrong
>
> On Thu, Apr 30, 2020 at 12:42 PM Matthias J. Sax <mj...@apache.org> wrote:
>
>>> Thanks for the information. So, does it mean that the state store
>> modified
>>>> locally by each application is replicated to all other applications?
>>
>> No. As long as the application runs "normally" (ie, without failure),
>> state is only maintained by one instance. In general, only in case of
>> failure, state would be migrated.
>>
>> You can configure "standby tasks" to pro-actively maintain state on
>> other instances, but it would not be on _all_ instances (depending on
>> your configuration) and the main purpose of standby tasks is to reduce
>> recovery time. Ie, even if you have standby task, that are "passive"
>> (you could only access them via IQ)
>>
>>
>> -Matthias
>>
>> On 4/29/20 9:06 PM, Pushkar Deole wrote:
>>> Thanks for the information. So, does it mean that the state store
>> modified
>>> locally by each application is replicated to all other applications? If
>> yes
>>> then does it happen in real time i.e. the state modified by an
>> application
>>> is immediately reflected in the state store of the other application?
>>>
>>>
>>> On Thu, Apr 30, 2020 at 12:18 AM Matthias J. Sax <mj...@apache.org>
>> wrote:
>>>
>>>> This might help:
>>>>
>>>>
>> https://stackoverflow.com/questions/40274884/is-kafka-stream-statestore-global-over-all-instances-or-just-local/40278168#40278168
>>>>
>>>> Note, that "global stores" are also "local" (ie, on local disk). The
>>>> difference is really between being sharded or being replicated.
>>>>
>>>>
>>>> -Matthias
>>>>
>>>> On 4/29/20 11:28 AM, Bill Bejeck wrote:
>>>>> Hi Pushkar,
>>>>>
>>>>> There is a concept of a global store
>>>>> <
>>>>
>> https://kafka.apache.org/25/javadoc/org/apache/kafka/streams/StreamsBuilder.html#addGlobalStore-org.apache.kafka.streams.state.StoreBuilder-java.lang.String-org.apache.kafka.streams.kstream.Consumed-org.apache.kafka.streams.processor.ProcessorSupplier-
>>>>> in
>>>>> Kafka Streams.
>>>>> The global state store has data from all partitions from the provided
>>>> input
>>>>> topic, unlike a "regular" state store that only has data for the
>>>> partitions
>>>>> of the streams task that owns the store.
>>>>> Note that global stores are still "local" because the store is
>>>> materialized
>>>>> on the machine running the streams app. But it's considered "global"
>>>>> because it accesses all partitions of the input topic for the store.
>>>>>
>>>>> HTH,
>>>>> Bill
>>>>>
>>>>> On Wed, Apr 29, 2020 at 6:09 AM Pushkar Deole <pd...@gmail.com>
>>>> wrote:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I am looking for some information as to whether kafka state store
>>>>>> KeyValueStore is global or local only. I found that it can be
>> in-memory
>>>> or
>>>>>> made persistent which stores it in local Rocksdb and also logging can
>> be
>>>>>> enabled so the state is backed by a topic which allows the state store
>>>> to
>>>>>> be fault tolerant.
>>>>>> However the information that I am looking for is: whether the state
>>>> store
>>>>>> can be global i.e. if the state written by one application is
>> available
>>>> to
>>>>>> the other application in real time even when both the applications are
>>>>>> running i.e. no rebalancing has triggered?
>>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>>
>
Re: are kafka state stores global or local?
Posted by Pushkar Deole <pd...@gmail.com>.
Thanks Matthias !
my question (So, does it mean that the state store modified locally by each
application is replicated to all other applications) was mainly about
"global state store",
As I understand it from your previous response, the state for global state
store would be replicated to all instances, please correct me if wrong
On Thu, Apr 30, 2020 at 12:42 PM Matthias J. Sax <mj...@apache.org> wrote:
> > Thanks for the information. So, does it mean that the state store
> modified
> >> locally by each application is replicated to all other applications?
>
> No. As long as the application runs "normally" (ie, without failure),
> state is only maintained by one instance. In general, only in case of
> failure, state would be migrated.
>
> You can configure "standby tasks" to pro-actively maintain state on
> other instances, but it would not be on _all_ instances (depending on
> your configuration) and the main purpose of standby tasks is to reduce
> recovery time. Ie, even if you have standby task, that are "passive"
> (you could only access them via IQ)
>
>
> -Matthias
>
> On 4/29/20 9:06 PM, Pushkar Deole wrote:
> > Thanks for the information. So, does it mean that the state store
> modified
> > locally by each application is replicated to all other applications? If
> yes
> > then does it happen in real time i.e. the state modified by an
> application
> > is immediately reflected in the state store of the other application?
> >
> >
> > On Thu, Apr 30, 2020 at 12:18 AM Matthias J. Sax <mj...@apache.org>
> wrote:
> >
> >> This might help:
> >>
> >>
> https://stackoverflow.com/questions/40274884/is-kafka-stream-statestore-global-over-all-instances-or-just-local/40278168#40278168
> >>
> >> Note, that "global stores" are also "local" (ie, on local disk). The
> >> difference is really between being sharded or being replicated.
> >>
> >>
> >> -Matthias
> >>
> >> On 4/29/20 11:28 AM, Bill Bejeck wrote:
> >>> Hi Pushkar,
> >>>
> >>> There is a concept of a global store
> >>> <
> >>
> https://kafka.apache.org/25/javadoc/org/apache/kafka/streams/StreamsBuilder.html#addGlobalStore-org.apache.kafka.streams.state.StoreBuilder-java.lang.String-org.apache.kafka.streams.kstream.Consumed-org.apache.kafka.streams.processor.ProcessorSupplier-
> >>> in
> >>> Kafka Streams.
> >>> The global state store has data from all partitions from the provided
> >> input
> >>> topic, unlike a "regular" state store that only has data for the
> >> partitions
> >>> of the streams task that owns the store.
> >>> Note that global stores are still "local" because the store is
> >> materialized
> >>> on the machine running the streams app. But it's considered "global"
> >>> because it accesses all partitions of the input topic for the store.
> >>>
> >>> HTH,
> >>> Bill
> >>>
> >>> On Wed, Apr 29, 2020 at 6:09 AM Pushkar Deole <pd...@gmail.com>
> >> wrote:
> >>>
> >>>> Hi,
> >>>>
> >>>> I am looking for some information as to whether kafka state store
> >>>> KeyValueStore is global or local only. I found that it can be
> in-memory
> >> or
> >>>> made persistent which stores it in local Rocksdb and also logging can
> be
> >>>> enabled so the state is backed by a topic which allows the state store
> >> to
> >>>> be fault tolerant.
> >>>> However the information that I am looking for is: whether the state
> >> store
> >>>> can be global i.e. if the state written by one application is
> available
> >> to
> >>>> the other application in real time even when both the applications are
> >>>> running i.e. no rebalancing has triggered?
> >>>>
> >>>
> >>
> >>
> >
>
>
Re: are kafka state stores global or local?
Posted by "Matthias J. Sax" <mj...@apache.org>.
> Thanks for the information. So, does it mean that the state store modified
>> locally by each application is replicated to all other applications?
No. As long as the application runs "normally" (ie, without failure),
state is only maintained by one instance. In general, only in case of
failure, state would be migrated.
You can configure "standby tasks" to pro-actively maintain state on
other instances, but it would not be on _all_ instances (depending on
your configuration) and the main purpose of standby tasks is to reduce
recovery time. Ie, even if you have standby task, that are "passive"
(you could only access them via IQ)
-Matthias
On 4/29/20 9:06 PM, Pushkar Deole wrote:
> Thanks for the information. So, does it mean that the state store modified
> locally by each application is replicated to all other applications? If yes
> then does it happen in real time i.e. the state modified by an application
> is immediately reflected in the state store of the other application?
>
>
> On Thu, Apr 30, 2020 at 12:18 AM Matthias J. Sax <mj...@apache.org> wrote:
>
>> This might help:
>>
>> https://stackoverflow.com/questions/40274884/is-kafka-stream-statestore-global-over-all-instances-or-just-local/40278168#40278168
>>
>> Note, that "global stores" are also "local" (ie, on local disk). The
>> difference is really between being sharded or being replicated.
>>
>>
>> -Matthias
>>
>> On 4/29/20 11:28 AM, Bill Bejeck wrote:
>>> Hi Pushkar,
>>>
>>> There is a concept of a global store
>>> <
>> https://kafka.apache.org/25/javadoc/org/apache/kafka/streams/StreamsBuilder.html#addGlobalStore-org.apache.kafka.streams.state.StoreBuilder-java.lang.String-org.apache.kafka.streams.kstream.Consumed-org.apache.kafka.streams.processor.ProcessorSupplier-
>>> in
>>> Kafka Streams.
>>> The global state store has data from all partitions from the provided
>> input
>>> topic, unlike a "regular" state store that only has data for the
>> partitions
>>> of the streams task that owns the store.
>>> Note that global stores are still "local" because the store is
>> materialized
>>> on the machine running the streams app. But it's considered "global"
>>> because it accesses all partitions of the input topic for the store.
>>>
>>> HTH,
>>> Bill
>>>
>>> On Wed, Apr 29, 2020 at 6:09 AM Pushkar Deole <pd...@gmail.com>
>> wrote:
>>>
>>>> Hi,
>>>>
>>>> I am looking for some information as to whether kafka state store
>>>> KeyValueStore is global or local only. I found that it can be in-memory
>> or
>>>> made persistent which stores it in local Rocksdb and also logging can be
>>>> enabled so the state is backed by a topic which allows the state store
>> to
>>>> be fault tolerant.
>>>> However the information that I am looking for is: whether the state
>> store
>>>> can be global i.e. if the state written by one application is available
>> to
>>>> the other application in real time even when both the applications are
>>>> running i.e. no rebalancing has triggered?
>>>>
>>>
>>
>>
>
Re: are kafka state stores global or local?
Posted by Pushkar Deole <pd...@gmail.com>.
Thanks for the information. So, does it mean that the state store modified
locally by each application is replicated to all other applications? If yes
then does it happen in real time i.e. the state modified by an application
is immediately reflected in the state store of the other application?
On Thu, Apr 30, 2020 at 12:18 AM Matthias J. Sax <mj...@apache.org> wrote:
> This might help:
>
> https://stackoverflow.com/questions/40274884/is-kafka-stream-statestore-global-over-all-instances-or-just-local/40278168#40278168
>
> Note, that "global stores" are also "local" (ie, on local disk). The
> difference is really between being sharded or being replicated.
>
>
> -Matthias
>
> On 4/29/20 11:28 AM, Bill Bejeck wrote:
> > Hi Pushkar,
> >
> > There is a concept of a global store
> > <
> https://kafka.apache.org/25/javadoc/org/apache/kafka/streams/StreamsBuilder.html#addGlobalStore-org.apache.kafka.streams.state.StoreBuilder-java.lang.String-org.apache.kafka.streams.kstream.Consumed-org.apache.kafka.streams.processor.ProcessorSupplier-
> >in
> > Kafka Streams.
> > The global state store has data from all partitions from the provided
> input
> > topic, unlike a "regular" state store that only has data for the
> partitions
> > of the streams task that owns the store.
> > Note that global stores are still "local" because the store is
> materialized
> > on the machine running the streams app. But it's considered "global"
> > because it accesses all partitions of the input topic for the store.
> >
> > HTH,
> > Bill
> >
> > On Wed, Apr 29, 2020 at 6:09 AM Pushkar Deole <pd...@gmail.com>
> wrote:
> >
> >> Hi,
> >>
> >> I am looking for some information as to whether kafka state store
> >> KeyValueStore is global or local only. I found that it can be in-memory
> or
> >> made persistent which stores it in local Rocksdb and also logging can be
> >> enabled so the state is backed by a topic which allows the state store
> to
> >> be fault tolerant.
> >> However the information that I am looking for is: whether the state
> store
> >> can be global i.e. if the state written by one application is available
> to
> >> the other application in real time even when both the applications are
> >> running i.e. no rebalancing has triggered?
> >>
> >
>
>
Re: are kafka state stores global or local?
Posted by "Matthias J. Sax" <mj...@apache.org>.
This might help:
https://stackoverflow.com/questions/40274884/is-kafka-stream-statestore-global-over-all-instances-or-just-local/40278168#40278168
Note, that "global stores" are also "local" (ie, on local disk). The
difference is really between being sharded or being replicated.
-Matthias
On 4/29/20 11:28 AM, Bill Bejeck wrote:
> Hi Pushkar,
>
> There is a concept of a global store
> <https://kafka.apache.org/25/javadoc/org/apache/kafka/streams/StreamsBuilder.html#addGlobalStore-org.apache.kafka.streams.state.StoreBuilder-java.lang.String-org.apache.kafka.streams.kstream.Consumed-org.apache.kafka.streams.processor.ProcessorSupplier->in
> Kafka Streams.
> The global state store has data from all partitions from the provided input
> topic, unlike a "regular" state store that only has data for the partitions
> of the streams task that owns the store.
> Note that global stores are still "local" because the store is materialized
> on the machine running the streams app. But it's considered "global"
> because it accesses all partitions of the input topic for the store.
>
> HTH,
> Bill
>
> On Wed, Apr 29, 2020 at 6:09 AM Pushkar Deole <pd...@gmail.com> wrote:
>
>> Hi,
>>
>> I am looking for some information as to whether kafka state store
>> KeyValueStore is global or local only. I found that it can be in-memory or
>> made persistent which stores it in local Rocksdb and also logging can be
>> enabled so the state is backed by a topic which allows the state store to
>> be fault tolerant.
>> However the information that I am looking for is: whether the state store
>> can be global i.e. if the state written by one application is available to
>> the other application in real time even when both the applications are
>> running i.e. no rebalancing has triggered?
>>
>
Re: are kafka state stores global or local?
Posted by Bill Bejeck <bi...@confluent.io>.
Hi Pushkar,
There is a concept of a global store
<https://kafka.apache.org/25/javadoc/org/apache/kafka/streams/StreamsBuilder.html#addGlobalStore-org.apache.kafka.streams.state.StoreBuilder-java.lang.String-org.apache.kafka.streams.kstream.Consumed-org.apache.kafka.streams.processor.ProcessorSupplier->in
Kafka Streams.
The global state store has data from all partitions from the provided input
topic, unlike a "regular" state store that only has data for the partitions
of the streams task that owns the store.
Note that global stores are still "local" because the store is materialized
on the machine running the streams app. But it's considered "global"
because it accesses all partitions of the input topic for the store.
HTH,
Bill
On Wed, Apr 29, 2020 at 6:09 AM Pushkar Deole <pd...@gmail.com> wrote:
> Hi,
>
> I am looking for some information as to whether kafka state store
> KeyValueStore is global or local only. I found that it can be in-memory or
> made persistent which stores it in local Rocksdb and also logging can be
> enabled so the state is backed by a topic which allows the state store to
> be fault tolerant.
> However the information that I am looking for is: whether the state store
> can be global i.e. if the state written by one application is available to
> the other application in real time even when both the applications are
> running i.e. no rebalancing has triggered?
>