David Jacot created KAFKA-12890:
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Summary: Consumer group stuck in `CompletingRebalance`
Key: KAFKA-12890
URL: https://issues.apache.org/jira/browse/KAFKA-12890
Project: Kafka
Issue Type: Bug
Affects Versions: 2.6.2, 2.7.1, 2.8.0, 2.6.1, 2.7.0
Reporter: David Jacot
Assignee: David Jacot
We have seen recently multiple consumer groups stuck in `CompletingRebalance`.
It appears that those group never receives the assignment from the leader of
the group and remains stuck in this state forever.
When a group transitions to the `CompletingRebalance` state, the group
coordinator sets up `DelayedHeartbeat` for each member of the group. It does so
to ensure that the member sends a sync request within the session timeout. If
it does not, the group coordinator rebalances the group. Note that here,
`DelayedHeartbeat` is used here for this purpose. `DelayedHeartbeat` are also
completed when member heartbeats.
The issue is that https://github.com/apache/kafka/pull/8834 has changed the
heartbeat logic to allow members to heartbeat while the group is in the
`CompletingRebalance` state. This was not allowed before. Now, if a member
starts to heartbeat while the group is in the `CompletingRebalance`, the
heartbeat request will basically complete the pending `DelayedHeartbeat` that
was setup previously for catching not receiving the sync request. Therefore, if
the sync request never comes, the group coordinator does not notice anymore.
We need to bring that behavior back somehow.
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