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Posted to jira@kafka.apache.org by "Lucas Bradstreet (Jira)" <ji...@apache.org> on 2021/06/04 14:15:00 UTC

[jira] [Created] (KAFKA-12896) Group rebalance loop caused by repeated group leader JoinGroups

Lucas Bradstreet created KAFKA-12896:
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             Summary: 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


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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