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https://issues.apache.org/jira/browse/KAFKA-21238?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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sanghyeok An updated KAFKA-21238:
---------------------------------
Labels: consumer group-coordinator (was: )
> Mutating nested sets in consumer assignor input can corrupt coordinator
> target assignment state
> -----------------------------------------------------------------------------------------------
>
> Key: KAFKA-21238
> URL: https://issues.apache.org/jira/browse/KAFKA-21238
> Project: Kafka
> Issue Type: Bug
> Reporter: sanghyeok An
> Assignee: sanghyeok An
> Priority: Minor
> Labels: consumer, group-coordinator
>
> *Description*
> {{MemberSubscriptionAndAssignmentImpl}} retains an {{Assignment}} that
> references the coordinator’s existing target assignment. Although
> {{Assignment}} wraps the outer map with
> {{{}Collections.unmodifiableMap(){}}}, the nested partition sets remain
> mutable.
> If a custom assignor uses the input assignment as a working data structure
> and modifies a nested set, it also modifies the coordinator’s existing target
> assignment before returning the assignment result.
>
> KS also had similar issue https://issues.apache.org/jira/browse/KAFKA-20846
> and it had been resolved.
>
> *Actual Behavior*
> A local reproduction of the Consumer path demonstrated the following:
> * The existing target assignment changes from \{0, 1} to \{1} during
> assignor execution.
> * {{TargetAssignmentBuilder}} considers the existing assignment and the
> returned result equal, so it does not generate a target assignment change
> record for the member.
> * The reverse index still retains the ownership information for partition 0.
> * Rolling back to the snapshot does not restore partition 0 in the nested
> set.
> This can leave the coordinator’s in-memory state, reverse index, and logged
> state inconsistent.
> *Expected Behavior*
> The input assignment provided to the assignor should be immutable and
> isolated from coordinator state. Attempts to modify nested partition sets
> should be rejected without affecting the coordinator’s existing target
> assignment.
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