[jira] [Commented] (KAFKA-12486) Utilize HighAvailabilityTaskAssignor to avoid downtime on corrupted task

["A. Sophie Blee-Goldman (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-12486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17303793#comment-17303793 ] 

A. Sophie Blee-Goldman commented on KAFKA-12486:
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Ideally we would only kick off a rebalance under certain conditions in which we can infer that this will help: for example, if the active task was in RUNNING or was within the acceptable.recovery.lag if in CREATED or RESTORING.  The reasoning here is that an active task in CREATED/RESTORING but with more than the acceptable.recovery.lag to restore would only have been assigned to this client if there were no other clients available who were considered to be caught-up. At the moment, the assignor has a yes/no take on the total lag, and won't take into consideration if there is another client who's not completely caught-up but has some amount of state (and is therefore preferable to restoring from scratch)
There are some other heuristics we could consider, such as whether the applications has standbys configured; if no standbys are used, the odds of another client maintaining an up-to-date copy of this state is lower (but not zero).

I don't think we necessarily need to add that much complexity from the get-go, but it's something to think about

> Utilize HighAvailabilityTaskAssignor to avoid downtime on corrupted task
> ------------------------------------------------------------------------
>
>                 Key: KAFKA-12486
>                 URL: https://issues.apache.org/jira/browse/KAFKA-12486
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: A. Sophie Blee-Goldman
>            Priority: Critical
>
> In KIP-441, we added the HighAvailabilityTaskAssignor to address certain common scenarios which tend to lead to heavy downtime for tasks, such as scaling out. The new assignor will always place an active task on a client which has a "caught-up" copy of that tasks' state, if any exists, while the intended recipient will instead get a standby task to warm up the state in the background. This way we keep tasks live as much as possible, and avoid the long downtime imposed by state restoration on active tasks.
> We can actually expand on this to reduce downtime due to restoring state: specifically, we may throw a TaskCorruptedException on an active task which leads to wiping out the state stores of that task and restoring from scratch. There are a few cases where this may be thrown:
>  # No checkpoint found with EOS
>  # TimeoutException when processing a StreamTask
>  # TimeoutException when committing offsets under eos
>  # RetriableException in RecordCollectorImpl
> (There is also the case of OffsetOutOfRangeException, but that is excluded here since it only applies to standby tasks).
> We should consider triggering a rebalance when we hit TaskCorruptedException on an active task, after we've wiped out the corrupted state stores. This will allow the assignor to temporarily redirect this task to another client who can resume work on the task while the original owner works on restoring the state from scratch.



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