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https://issues.apache.org/jira/browse/KAFKA-4677?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Damian Guy updated KAFKA-4677:
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Summary: Avoid unnecessary task movement across threads of the same process
during rebalance (was: Make StreamPartitionAssigner more sticky when assigning
to threads)
> Avoid unnecessary task movement across threads of the same process during
> rebalance
> -----------------------------------------------------------------------------------
>
> Key: KAFKA-4677
> URL: https://issues.apache.org/jira/browse/KAFKA-4677
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 0.10.2.0
> Reporter: Damian Guy
> Assignee: Damian Guy
> Fix For: 0.10.3.0
>
>
> StreamPartitionAssigner tries to follow a sticky assignment policy to avoid
> expensive task migration. Currently, it does this in a best-effort approach.
> We could observe a case, for which tasks did migrate for no good reason, thus
> we assume that the current implementation could be improved to be more sticky.
> The concrete scenario is as follows:
> assume we have topology with 3 tasks, A, B, C
> assume we have 3 threads, each executing one task: 1-A, 2-B, 3-C
> for some reason, thread 1 goes down and a rebalance gets triggered
> thread 2 and 3 get their partitions revoked
> sometimes (not sure what the exact condition for this is), the new assignment
> flips the assignment for task B and C (task A is newly assigned to either
> thread 2 or 3)
> > possible new assignment 2(A,C) and 3-B
> There is no obvious reason (like load-balancing) why the task assignment for
> B and C does change to the other thread resulting in unnecessary task
> migration.
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