[jira] [Commented] (KAFKA-19682) Improve logging about task readiness

["Lucy Liu (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-19682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18029115#comment-18029115 ] 

Lucy Liu commented on KAFKA-19682:
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Hi [~qyte] , 

I saw you picked ticket and wanted to check if you are actively working on it? I'm doing a patch for this but forgot to assign this to myself – my apologies for the confusion.

If you haven't had a chance to start, I have some capacity and would be happy to pick this up. Please let me know what works for you. Thanks!

> Improve logging about task readiness
> ------------------------------------
>
>                 Key: KAFKA-19682
>                 URL: https://issues.apache.org/jira/browse/KAFKA-19682
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Matthias J. Sax
>            Assignee: Tanmay Datey
>            Priority: Minor
>
> Kafka Streams processes its assigned tasks in a round robin fashion, however, if a task is considered not ready for processing, it might get skipped. We have observed cases, in which Kafka Streams seems to get stuck on a partition, and restarting the application instance resolves this issue. We suspect, it's related to considering the task for the stuck partition as not ready for processing. (As the ready/not-ready decision is based on in-memory state of KS runtime, bouncing the instance would reset KS runtime into a clean state, unblocking the stuck task.)
> However, we currently don't have sufficient logging to reason about this case, and to understand if and why a task might be skipped. We should add more log statement (DEBUG and/or TRACE) to get better visibility. There might be a lurking bug in this logic that we cannot narrow down w/o the corresponding information logging could provide.



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