[jira] [Created] (KAFKA-19974) Partitions can be assigned to more than one member in the same epoch

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

Sean Quah created KAFKA-19974:
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             Summary: Partitions can be assigned to more than one member in the same epoch
                 Key: KAFKA-19974
                 URL: https://issues.apache.org/jira/browse/KAFKA-19974
             Project: Kafka
          Issue Type: Bug
          Components: group-coordinator
            Reporter: Sean Quah
            Assignee: Sean Quah
             Fix For: 4.2.0


NB: This bug is not about partitions being assigned to more than one member simultaneously.

The change for KAFKA-19431 introduced a case where two different members could be assigned a partition in the same epoch (but not at the same time).

When transitioning from UNREVOKED_PARTITIONS to UNREVOKED_PARTITIONS, we bump the member epoch. However, we cannot tell whether we had unrevoked partitions due to an unsubscription or an assignment change. When the unrevoked partitions are due to an unsubscription, we may bump to an epoch where other partitions are supposed to be assigned to a different member.

Example:

A group contains two members, both stable at epoch 10. The target assignment is at epoch 10.
 # Member A unsubscribes from topic bar at epoch 10. It enters UNREVOKED_PARTITIONS at epoch 10 { assigned partitions: [foo], pending revocation: [bar] }
 # A new target assignment for epoch 11 moves partition foo to member B.
 # Member A heartbeats at epoch 10, yielding bar. We try to reconcile to the target assignment and it enters UNREVOKED_PARTITIONS again, at epoch 11 { assigned partitions: [], pending revocation: [foo] }
 # Member A yields topic foo.
 # Member B is assigned topic foo at epoch 11 \{ assigned partitions [foo] }



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