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https://issues.apache.org/jira/browse/KAFKA-4509?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on KAFKA-4509 started by Matthias J. Sax.
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> Task reusage on rebalance fails for threads on same host
> --------------------------------------------------------
>
> Key: KAFKA-4509
> URL: https://issues.apache.org/jira/browse/KAFKA-4509
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Matthias J. Sax
>
> In https://issues.apache.org/jira/browse/KAFKA-3559 task reusage on rebalance
> was introduces as a performance optimization. Instead of closing a task on
> rebalance (ie, {{onPartitionsRevoked()}}, it only get's suspended for a
> potential reuse in {{onPartitionsAssigned()}}. Only if a task cannot be
> reused, it will eventually get closed in {{onPartitionsAssigned()}}.
> This mechanism can fail, if multiple {{StreamThreads}} run in the same host
> (same or different JVM). The scenario is as follows:
> - assume 2 running threads A and B
> - assume 3 tasks t1, t2, t3
> - assignment: A-(t1,t2) and B-(t3)
> - on the same host, a new single threaded Stream application (same app-id)
> gets started (thread C)
> - on rebalance, t2 (could also be t1 -- does not matter) will be moved from
> A to C
> - as assignment is only sticky base on an heurictic t1 can sometimes be
> assigned to B, too -- and t3 get's assigned to A (thre is a race condition if
> this "task flipping" happens or not)
> - on revoke, A will suspend task t1 and t2 (not releasing any locks)
> - on assign
> - A tries to create t3 but as B did not release it yet, A dies with an
> "cannot get lock" exception
> - B tries to create t1 but as A did not release it yet, B dies with an
> "cannot get lock" exception
> - as A and B trie to create the task first, this will always fail if task
> flipping happened
> - C tries to create t2 but A did not release t2 lock yet (race condition)
> and C dies with an exception (this could even happen without "task flipping"
> between A and B)
> We want to fix this, by:
> # first release unassigned suspended tasks in {{onPartitionsAssignment()}},
> and afterward create new tasks (this fixes the "task flipping" issue)
> # use a "backoff and retry mechanism" if a task cannot be created (to
> handle release-create race condition between different threads)
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