[jira] [Updated] (KAFKA-18687) New group coordinator triggers assignment recalculation on consumer group upgrade due to static member replacement

["Sean Quah (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-18687?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Quah updated KAFKA-18687:
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    Component/s: group-coordinator

> 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
>
> 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].



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