[jira] [Created] (KAFKA-3886) Consumer should handle wakeups while rebalancing more gracefully

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

Jason Gustafson created KAFKA-3886:
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             Summary: Consumer should handle wakeups while rebalancing more gracefully
                 Key: KAFKA-3886
                 URL: https://issues.apache.org/jira/browse/KAFKA-3886
             Project: Kafka
          Issue Type: Bug
          Components: consumer
    Affects Versions: 0.10.0.0
            Reporter: Jason Gustafson
            Assignee: Jason Gustafson


If the user calls wakeup() while a rebalance in progress, we currently lose track of the state of that rebalance. In the worst case, this can result in an additional unneeded rebalance when the user calls poll() again. 

The other thing that can happen is that the rebalance could complete inside another blocking call (e.g. {{commitSync()}}). There may be scenarios where this can cause us to commit offsets outside. For example: 

1. Consumer is initially assigned partition A
2. The consumer starts rebalancing, but is interrupted with a call to wakeup().
3. User calls commitSync with offsets (A, 5)
4. Before offset commit is sent, an interrupted rebalance completes and changes the assignment to include only partition B.
5. Now we proceed with the unsafe offset commit on partition A.

In this case, we should probably ensure that it is not possible to commit offsets after an assignment has been revoked. Other cases, such as position(), may be handled similarly.



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