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https://issues.apache.org/jira/browse/KAFKA-21167?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matthias J. Sax updated KAFKA-21167:
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Component/s: group-coordinator
streams
> StickyTaskAssignor can overlook local state when a member reaches quota
> -----------------------------------------------------------------------
>
> Key: KAFKA-21167
> URL: https://issues.apache.org/jira/browse/KAFKA-21167
> Project: Kafka
> Issue Type: Bug
> Components: group-coordinator, streams
> Reporter: sanghyeok An
> Assignee: sanghyeok An
> Priority: Minor
> Labels: streams
>
> The broker-side StickyTaskAssignor selects a previous-state candidate before
> checking its quota. A member at quota can prevent another eligible member in
> the same process from being selected, causing unnecessary state restoration.
>
> There are three stateful tasks and five members, giving an active task quota
> of one per member:
> * Process P has two members: p1 previously owned task 0, and p2 had no
> active tasks. Both report local state for task 2.
> * Process Q has three members: q1 previously owned task 1, while q2 and q3
> had no active tasks. None report local state for task 2.
> After tasks 0 and 1 are retained, p1 is at quota while p2 remains available.
> If p1 is considered first, p2 cannot replace it because both members have the
> same process load. The subsequent quota check rejects p1 without trying p2.
> Task 2 then falls back to load-based assignment, which selects Q because its
> load is 1/3, compared with P's 1/2 even if p2 has local state for task 2.
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