[jira] [Created] (KAFKA-4704) Group coordinator cache loading fails if groupId is used first for consumer groups and then for simple consumer

["Jason Gustafson (JIRA)" <ji...@apache.org>]

Jason Gustafson created KAFKA-4704:
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             Summary: Group coordinator cache loading fails if groupId is used first for consumer groups and then for simple consumer
                 Key: KAFKA-4704
                 URL: https://issues.apache.org/jira/browse/KAFKA-4704
             Project: Kafka
          Issue Type: Bug
    Affects Versions: 0.10.1.1, 0.10.1.0, 0.10.0.1, 0.10.0.0
            Reporter: Jason Gustafson
            Assignee: Jason Gustafson
             Fix For: 0.10.2.0


When all the members in a consumer group have died and all of its offsets have expired, we write a tombstone to __consumer_offsets so that its group metadata is cleaned up. It is possible that after this happens, the same groupId is then used only for offset storage (i.e. by "simple" consumers). Our current cache loading logic, which is triggered when a coordinator first takes over control of a partition, does not account for this scenario and would currently fail.

This is probably an unlikely scenario to hit in practice, but it reveals the lack of test coverage around the cache loading logic. We should improve this.



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