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https://issues.apache.org/jira/browse/KAFKA-12679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17847334#comment-17847334
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Lucas Brutschy edited comment on KAFKA-12679 at 5/17/24 2:26 PM:
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Hey [~stoeckmk]. It is true that the state updater was not enabled in 3.7 in
the end, so there is no back-off when locking the state directory. We missed
updating the fix version on this ticket. I updated it now.
Hey [~coltmcnealy-lh]. The change I implemented was to back-off in case of a
lock error, but essentially retry. You should see something like `"Encountered
lock exception. Reattempting locking the state in the next iteration.` If you
are completely stuck and the application makes zero progress, this does not
seem like it would be solved by a back-off, and somehow that seems to describe
a different problem, especially if it also happens with state updater enabled.
We may want to create a separate ticket for this, since the problem described
in this ticket should resolve itself once the old thread releases the lock on
the state directory.
was (Author: JIRAUSER302322):
Hey [~coltmcnealy-lh]. It is true that the state updater was not enabled in 3.7
in the end, so there is no back-off when locking the state directory. The
change I implemented was to back-off in case of a lock error, to not end up in
a busy loop trying to acquire the lock. If you are completely stuck and the
application makes zero progress, this does not seem like it would be solved by
a back-off, and somehow that seems to describe a different problem, especially
if it also happens with state updater enabled.
We may want to create a separate ticket for this, since the problem described
in this ticket should resolve itself once the old thread releases the lock on
the state directory.
Either way, I'll update the fix version here.
> Rebalancing a restoring or running task may cause directory livelocking with
> newly created task
> -----------------------------------------------------------------------------------------------
>
> Key: KAFKA-12679
> URL: https://issues.apache.org/jira/browse/KAFKA-12679
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.6.1
> Environment: Broker and client version 2.6.1
> Multi-node broker cluster
> Multi-node, auto scaling streams app instances
> Reporter: Peter Nahas
> Assignee: Lucas Brutschy
> Priority: Major
> Fix For: 3.8.0
>
> Attachments: Backoff-between-directory-lock-attempts.patch
>
>
> If a task that uses a state store is in the restoring state or in a running
> state and the task gets rebalanced to a separate thread on the same instance,
> the newly created task will attempt to lock the state store director while
> the first thread is continuing to use it. This is totally normal and expected
> behavior when the first thread is not yet aware of the rebalance. However,
> that newly created task is effectively running a while loop with no backoff
> waiting to lock the directory:
> # TaskManager tells the task to restore in `tryToCompleteRestoration`
> # The task attempts to lock the directory
> # The lock attempt fails and throws a
> `org.apache.kafka.streams.errors.LockException`
> # TaskManager catches the exception, stops further processing on the task
> and reports that not all tasks have restored
> # The StreamThread `runLoop` continues to run.
> I've seen some documentation indicate that there is supposed to be a backoff
> when this condition occurs, but there does not appear to be any in the code.
> The result is that if this goes on for long enough, the lock-loop may
> dominate CPU usage in the process and starve out the old stream thread task
> processing.
>
> When in this state, the DEBUG level logging for TaskManager will produce a
> steady stream of messages like the following:
> {noformat}
> 2021-03-30 20:59:51,098 DEBUG --- [StreamThread-10] o.a.k.s.p.i.TaskManager
> : stream-thread [StreamThread-10] Could not initialize 0_34 due
> to the following exception; will retry
> org.apache.kafka.streams.errors.LockException: stream-thread
> [StreamThread-10] standby-task [0_34] Failed to lock the state directory for
> task 0_34
> {noformat}
>
>
> I've attached a git formatted patch to resolve the issue. Simply detect the
> scenario and sleep for the backoff time in the appropriate StreamThread.
>
>
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