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https://issues.apache.org/jira/browse/KAFKA-18687?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Jacot resolved KAFKA-18687.
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Fix Version/s: 4.0.1
4.1.0
Resolution: Fixed
> New group coordinator triggers assignment recalculation on consumer group
> upgrade due to static member replacement
> ------------------------------------------------------------------------------------------------------------------
>
> Key: KAFKA-18687
> URL: https://issues.apache.org/jira/browse/KAFKA-18687
> Project: Kafka
> Issue Type: Bug
> Components: group-coordinator
> Reporter: Sean Quah
> Assignee: Dongnuo Lyu
> Priority: Minor
> Fix For: 4.0.1, 4.1.0
>
>
> When a consumer protocol static member replaces an existing member in a
> classic group, it's not necessary to recompute the assignment. However, it
> happens anyway.
> In
> [ConsumerGroup.fromClassicGroup|https://github.com/apache/kafka/blob/0ff4dafb7de4e24ddb7961d52e50e728f2eee4eb/group-coordinator/src/main/java/org/apache/kafka/coordinator/group/modern/consumer/ConsumerGroup.java#L1140],
> we don't set the group's subscriptionMetadata.
> Later in the consumer group heartbeat, we [call
> updateSubscriptionMetadata|https://github.com/apache/kafka/blob/0ff4dafb7de4e24ddb7961d52e50e728f2eee4eb/group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupMetadataManager.java#L1748],
> which [notices that the group's subscriptionMetadata needs an
> update|https://github.com/apache/kafka/blob/0ff4dafb7de4e24ddb7961d52e50e728f2eee4eb/group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupMetadataManager.java#L2757]
> and bumps the epoch. Since the epoch is bumped, we [recompute the
> assignment|https://github.com/apache/kafka/blob/0ff4dafb7de4e24ddb7961d52e50e728f2eee4eb/group-coordinator/src/main/java/org/apache/kafka/coordinator/group/GroupMetadataManager.java#L1766].
> As a fix, we can try setting the subscriptionMetadata in
> ConsumerGroup.fromClassicGroup.
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