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From Bruno Cadonna <br...@confluent.io>
Subject Re: Needless group coordination overhead for GlobalKTables
Date Fri, 01 Nov 2019 08:44:29 GMT
Thank you for reaching out and filing the ticket.

Best,
Bruno

On Fri, Nov 1, 2019 at 3:19 AM Chris Toomey <ctoomey@gmail.com> wrote:
>
> Thanks Bruno, filed https://issues.apache.org/jira/browse/KAFKA-9127 .
>
> On Wed, Oct 30, 2019 at 2:06 AM Bruno Cadonna <bruno@confluent.io> wrote:
>
> > Hi Chris,
> >
> > Thank you for the clarification. Now I see what you mean. If your
> > topology works correctly, I would not file it as a bug but as a
> > possible improvement.
> >
> > Best,
> > Bruno
> >
> > On Wed, Oct 30, 2019 at 1:20 AM Chris Toomey <ctoomey@gmail.com> wrote:
> > >
> > > Bruno,
> > >
> > > I'm using a fork based off the 2.4 branch .It's not the global consumer
> > but
> > > the stream thread consumer that has the group id since it's built with
> > the
> > > main consumer config:
> > >
> > https://github.com/apache/kafka/blob/065411aa2273fd393e02f0af46f015edfc9f9b55/streams/src/main/java/org/apache/kafka/streams/StreamsConfig.java#L1051
> > >  .
> > >
> > > It shouldn't be creating a regular consumer for the topic since my
> > topology
> > > only has a single element, the GlobalKTable, which is populated by the
> > > global consumer. My scala code:
> > >
> > > val builder: StreamsBuilder = new StreamsBuilder()
> > > val gTable = builder.globalTable[K, V](...)
> > > val stream = new KafkaStreams(builder.build(), props)
> > > stream.start()
> > >
> > >
> > > I can disable the stream thread consumer by configuring
> > num.stream.threads
> > > = 0, but why does it create this stream thread consumer in the first
> > place
> > > if it's not been requested in the topology?
> > >
> > > thx,
> > > Chris
> > >
> > > On Tue, Oct 29, 2019 at 2:08 PM Bruno Cadonna <bruno@confluent.io>
> > wrote:
> > >
> > > > Hi Chris,
> > > >
> > > > What version of Streams are you referring to?
> > > >
> > > > On the current trunk the group.id property is removed from the config
> > > > for the global consumer that populates the GlobalKTable.
> > > >
> > > > See the following code line
> > > >
> > > >
> > https://github.com/apache/kafka/blob/065411aa2273fd393e02f0af46f015edfc9f9b55/streams/src/main/java/org/apache/kafka/streams/StreamsConfig.java#L1149
> > > >
> > > > Best,
> > > > Bruno
> > > >
> > > > On Tue, Oct 29, 2019 at 8:12 PM Chris Toomey <ctoomey@gmail.com>
> > wrote:
> > > > >
> > > > > We have some simple Kafka streams apps that populate GlobalKTables
> > to use
> > > > > as caches for topic contents. When running them with info-level
> > logging
> > > > > enabled, I noticed unexpected activity around group coordination
> > > > (joining,
> > > > > rebalancing, leaving, rejoining) that I didn't expect given that
they
> > > > need
> > > > > to consume from all topic partitions vs. use the group load balancing
> > > > > feature.
> > > > >
> > > > > I tracked this down to the way the consumer config. is generated
for
> > > > > a GlobalKTable consumer -- the groupId is set to the Kafka streams
> > > > > application id instead of to null -- the consumer needlessly creates
> > a
> > > > > ConsumerCoordinator and thus intiiates all the needless associated
> > > > > messaging and overhead.
> > > > >
> > > > > I was going to file a bug for this but per the contributing page
am
> > > > > bringing this up here first. Is there a reason why GlobalKTable
> > consumers
> > > > > should bear this group coordination overhead or should I go ahead
and
> > > > file
> > > > > a ticket to remove it?
> > > > >
> > > > > thanks,
> > > > > Chris
> > > >
> >

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