[jira] [Commented] (KAFKA-4175) Can't have StandbyTasks in KafkaStreams where NUM_STREAM_THREADS_CONFIG > 1

["Guozhang Wang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-4175?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15493763#comment-15493763 ] 

Guozhang Wang commented on KAFKA-4175:
--------------------------------------

[~damianguy] Thanks for the finding. I think this was overlooked originally when we handle {{OverlappingFileLockException}}, that since {{FileChannel.tryLock}} is not bound to the thread, but is for the whole JVM, we thought returning null is sufficient. But it obviously is not the case.

> Can't have StandbyTasks in KafkaStreams where NUM_STREAM_THREADS_CONFIG > 1
> ---------------------------------------------------------------------------
>
>                 Key: KAFKA-4175
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4175
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 0.10.1.0
>            Reporter: Damian Guy
>            Assignee: Guozhang Wang
>             Fix For: 0.10.1.0
>
>
> When we have StandbyTasks in a Kafka Streams app and we have > 1 threads per instance we can run into:
> {code}
> Caused by: java.io.IOException: task [1_0] Failed to lock the state directory: /private/tmp/kafka-streams-smoketest/2/SmokeTest/1_0
> {code}
> This is because the StandbyTask has been assigned to the same KafkaStreams instance as the active task. We need to either use a different base state directory for the standby tasks or we need to change the assignment such that they don't end up in the same instance. 



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