[jira] [Created] (KAFKA-4677) Make StreamPartitionAssigner more sticky when assigning to threads

["Damian Guy (JIRA)" <ji...@apache.org>]

Damian Guy created KAFKA-4677:
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             Summary: Make StreamPartitionAssigner more sticky when assigning to threads
                 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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