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https://issues.apache.org/jira/browse/KAFKA-9821?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sophie Blee-Goldman resolved KAFKA-9821.
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Resolution: Fixed
> Stream task may skip assignment with static members and incremental rebalances
> ------------------------------------------------------------------------------
>
> Key: KAFKA-9821
> URL: https://issues.apache.org/jira/browse/KAFKA-9821
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.4.0
> Reporter: Guozhang Wang
> Assignee: Sophie Blee-Goldman
> Priority: Major
> Fix For: 2.6.0
>
>
> When static membership (KIP-345) and incremental rebalancing (KIP-429) are
> turned on at the same time, that upon failure it is possible some partitions
> are not assigned to anyone. The event sequence is the following:
> 1. An assignment (task1) from rebalance is sent to an existing static member
> with owned list (partition1, partition2), hence upon receiving the assignment
> the static member is supposed to revoke partition2 and then re-join the group
> to trigger another rebalance.
> 2. The member crashed before re-join the group, lost all of its assigned
> partitions. However since this member is static with long session timeout, it
> was not kicked out of the group yet at the coordinator side.
> 3. The member resumes and then re-join with a known instance.id. The
> coordinator would not trigger a rebalance in this case and just give it the
> previous assignment (partition1), and since the member has forgot about its
> previous owned partitions it would just take partition1 and not re-join.
> 4. As a result the partition2 is not owned by this member any more but not
> re-assigned to anyone; until the next rebalance it would not be fetched by
> any member of the group.
> The key here is that today we are relying on the member's local memory to
> calculate the added / revoked diff based on (owned, assigned). But if the
> member crashed and lost all of its owned partition, AND if it is a static
> member whose re-join would not trigger a new rebalance, this will break.
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