[jira] [Commented] (KAFKA-345) Add a listener to ZookeeperConsumerConnector to get notified on rebalance events

["Peter Romianowski (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13279022#comment-13279022 ] 

Peter Romianowski commented on KAFKA-345:
-----------------------------------------

I tried to add a test to verify that the listener gets called if an error occurs (ConsumerListener#afterRebalance(false)) but I failed to introduce some error into ZookeeperConsumerConnector.ZKRebalancerListener#syncedRebalance. 

Any ideas how to provoke an error during rebalancing?
                
> Add a listener to ZookeeperConsumerConnector to get notified on rebalance events
> --------------------------------------------------------------------------------
>
>                 Key: KAFKA-345
>                 URL: https://issues.apache.org/jira/browse/KAFKA-345
>             Project: Kafka
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 0.7, 0.8
>            Reporter: Peter Romianowski
>         Attachments: KAFKA-345.patch
>
>
> A sample use-case
> In our scenario we partition events by userid and then apply these to some kind of state machine, that modifies the actual state of a user. So events trigger state transitions. In order to avoid the need of loading user's state upon each event processed, we cache that. But if a user's partition is moved to another consumer and then back to the previous consumer we have stale caches and hell breaks loose. I guess the same kind of problem occurs in other scenarios like counting numbers by user, too.

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