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https://issues.apache.org/jira/browse/KAFKA-12896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17367805#comment-17367805
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A. Sophie Blee-Goldman commented on KAFKA-12896:
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I believe this is caused by https://issues.apache.org/jira/browse/KAFKA-12984,
which in turn is caused by https://issues.apache.org/jira/browse/KAFKA-12983.
I'll prepare a fix for both of these issues
> Group rebalance loop caused by repeated group leader JoinGroups
> ---------------------------------------------------------------
>
> Key: KAFKA-12896
> URL: https://issues.apache.org/jira/browse/KAFKA-12896
> Project: Kafka
> Issue Type: Bug
> Components: clients
> Affects Versions: 2.6.0
> Reporter: Lucas Bradstreet
> Assignee: David Jacot
> Priority: Blocker
> Fix For: 3.0.0
>
>
> We encountered a strange case of a rebalance loop with the
> "cooperative-sticky" assignor. The logs show the following for several hours:
>
> {{Apr 7, 2021 @ 03:58:36.040 [GroupCoordinator 7]: Stabilized group mygroup
> generation 19830137 (__consumer_offsets-7)}}
> {{Apr 7, 2021 @ 03:58:35.992 [GroupCoordinator 7]: Preparing to rebalance
> group mygroup in state PreparingRebalance with old generation 19830136
> (__consumer_offsets-7) (reason: Updating metadata for member
> mygroup-1-7ad27e07-3784-4588-97e1-d796a74d4ecc during CompletingRebalance)}}
> {{Apr 7, 2021 @ 03:58:35.988 [GroupCoordinator 7]: Stabilized group mygroup
> generation 19830136 (__consumer_offsets-7)}}
> {{Apr 7, 2021 @ 03:58:35.972 [GroupCoordinator 7]: Preparing to rebalance
> group mygroup in state PreparingRebalance with old generation 19830135
> (__consumer_offsets-7) (reason: Updating metadata for member mygroup during
> CompletingRebalance)}}
> {{Apr 7, 2021 @ 03:58:35.965 [GroupCoordinator 7]: Stabilized group mygroup
> generation 19830135 (__consumer_offsets-7)}}
> {{Apr 7, 2021 @ 03:58:35.953 [GroupCoordinator 7]: Preparing to rebalance
> group mygroup in state PreparingRebalance with old generation 19830134
> (__consumer_offsets-7) (reason: Updating metadata for member
> mygroup-7ad27e07-3784-4588-97e1-d796a74d4ecc during CompletingRebalance)}}
> {{Apr 7, 2021 @ 03:58:35.941 [GroupCoordinator 7]: Stabilized group mygroup
> generation 19830134 (__consumer_offsets-7)}}
> {{Apr 7, 2021 @ 03:58:35.926 [GroupCoordinator 7]: Preparing to rebalance
> group mygroup in state PreparingRebalance with old generation 19830133
> (__consumer_offsets-7) (reason: Updating metadata for member mygroup during
> CompletingRebalance)}}
> Every single time, it was the same member that triggered the JoinGroup and it
> was always the leader of the group.{{}}
> The leader has the privilege of being able to trigger a rebalance by sending
> `JoinGroup` even if its subscription metadata has not changed. But why would
> it do so?
> It is possible that this is due to the same issue or a similar bug to
> https://issues.apache.org/jira/browse/KAFKA-12890.
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