[jira] [Resolved] (KAFKA-10086) Standby state isn't always re-used when transitioning to active

["John Roesler (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-10086?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

John Roesler resolved KAFKA-10086.
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    Resolution: Fixed

> Standby state isn't always re-used when transitioning to active
> ---------------------------------------------------------------
>
>                 Key: KAFKA-10086
>                 URL: https://issues.apache.org/jira/browse/KAFKA-10086
>             Project: Kafka
>          Issue Type: Task
>          Components: streams
>    Affects Versions: 2.6.0, 2.7.0
>            Reporter: John Roesler
>            Assignee: John Roesler
>            Priority: Blocker
>             Fix For: 2.6.0, 2.7.0
>
>
> This ticket was initially just to write an integration test, but I escalated it to a blocker and changed the title when the integration test actually surfaced two bugs:
>  # Offset positions were not reported for in-memory stores, so tasks with in-memory stores would never be considered as "caught up" and could not take over active processing, preventing clusters from ever achieving balance. This is a regression in 2.6
>  # When the TaskAssignor decided to switch active processing from a former owner to a new one that had a standby, the lower-level cooperative rebalance protocol would first de-schedule the task completely, and only later would assign it to the new owner. For in-memory stores, this causes the standby state not to be re-used, and for persistent stores, it creates a window in which the cleanup thread might delete the state directory. In both cases, even though the instance previously had a standby, once it gets the active, it still had to restore the entire state from the changelog.



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