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https://issues.apache.org/jira/browse/KAFKA-21360?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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이선민 updated KAFKA-21360:
------------------------
Priority: Minor (was: Trivial)
> Heterogeneous simple share assignor keeps partitions of topics that no member
> subscribes to
> -------------------------------------------------------------------------------------------
>
> Key: KAFKA-21360
> URL: https://issues.apache.org/jira/browse/KAFKA-21360
> Project: Kafka
> Issue Type: Bug
> Components: group-coordinator
> Affects Versions: 4.2.0
> Reporter: 이선민
> Assignee: 이선민
> Priority: Minor
>
> SimpleHeterogeneousAssignmentBuilder#build computes the assignment for each
> topic in the union of the members' subscriptions. A topic that no member
> subscribes to anymore is never visited, so a member whose existing assignment
> contains it gets its old partitions for that topic carried over into the new
> target assignment.
> For the same reason, the {{else}} branch in
> {{TopicAssignmentPartialBuilder#revokeUnassignablePartitions}} that removes
> the topic is
> unreachable, since {{topicId}} always comes from {{subscribedTopicIds}} there.
> The homogeneous builder handles this case correctly:
> {{SimpleHomogeneousAssignmentBuilder}}
> iterates over each member's existing assignment and removes topics that are
> no longer subscribed.
> This behavior has been present since the builder was introduced by KAFKA-19363
> (https://github.com/apache/kafka/pull/20074), and is present in 4.2.0.
> h3. Reproduction
> Invoke {{SimpleAssignor#assign}} with the following group specification:
> * Topics: T1 (4 partitions), T2 (2 partitions), T3 (2 partitions)
> * Member A subscribes to {T1}, existing assignment {T1=[0], T2=[0]}
> * Member B subscribes to {T1, T3}, existing assignment {T1=[1], T2=[1]}
> * Subscription type: HETEROGENEOUS
> Actual assignor output (one observed run):
> {noformat}
> A={T2=[0], T1=[0, 2]}
> B={T2=[1], T1=[1, 3], T3=[0, 1]}
> {noformat}
> Expected result: T2 is revoked from both members.
> h3. Impact
> Since KAFKA-19431, {{ShareGroupAssignmentBuilder}} filters out topics outside
> each member's subscription when reconciling the target assignment into the
> member's current assignment, so these stale partitions are not passed on to
> members.
> This filtering does not modify the stored target assignment. The stale
> entries can therefore
> survive subsequent rebalances while the group remains heterogeneous and no
> member subscribes to the topic.
> This was found while adding tests in
> https://github.com/apache/kafka/pull/23874, where it was confirmed as a bug
> in review
> (https://github.com/apache/kafka/pull/23874#issuecomment-6394163465).
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