[GitHub] [kafka] C0urante commented on pull request #12622: Update WorkerSinkTask.java

[GitBox <gi...@apache.org>]

C0urante commented on PR #12622:
URL: https://github.com/apache/kafka/pull/12622#issuecomment-1245423635

   Thanks @kumarpritam863, this is an important fix. I did some research on the history behind incremental consumer rebalancing and how it relates to the rebalance listener API, and found that [this PR](https://github.com/apache/kafka/pull/6884#issue-452279459) contained some great details, including an explicit confirmation on the expected ordering of callback invocation:
   
   > The ordering of the callback would be the following:
   a. Callback onPartitionsRevoked / onPartitionsLost triggered.
   b. Update the assignment (both revoked and added).
   c. Callback onPartitionsAssigned triggered.
   
   One case I'm wondering about is when the task fails, which would cause its consumer to leave the group. I believe that this would cause `onPartitionsRevoked` to be invoked in the rebalance listener, but not `onPartitionsAssigned`, so the metrics for the task (which are still available for failed tasks until they are explicitly revoked from the worker) would become inaccurate.
   
   Could we forcibly reset the partition count metric to zero in `WorkerSinkTask::close` to address this case? (Probably with a brief comment explaining why we have this special logic).
   
   It'd also be nice to see some tests for this logic, both to verify correctness and help prevent regression.


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