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https://issues.apache.org/jira/browse/KAFKA-1096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14039470#comment-14039470
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Sriharsha Chintalapani commented on KAFKA-1096:
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Updated reviewboard https://reviews.apache.org/r/22496/diff/
against branch origin/trunk
> An old controller coming out of long GC could update its epoch to the latest
> controller's epoch
> -----------------------------------------------------------------------------------------------
>
> Key: KAFKA-1096
> URL: https://issues.apache.org/jira/browse/KAFKA-1096
> Project: Kafka
> Issue Type: Bug
> Components: controller
> Affects Versions: 0.8.0
> Reporter: Swapnil Ghike
> Assignee: Sriharsha Chintalapani
> Fix For: 0.8.2
>
> Attachments: KAFKA-1096.patch, KAFKA-1096_2014-06-20_15:27:44.patch
>
>
> If a controller GCs for too long, we could have two controllers in the
> cluster. The controller epoch is supposed to minimize the damage in such a
> situation, as the brokers will reject the requests sent by the controller
> with an older epoch.
> When the old controller is still in long GC, a new controller could be
> elected. This will fire ControllerEpochListener on the old controller. When
> it comes out of GC, its ControllerEpochListener will update its own epoch to
> the new controller's epoch. So both controllers are now able to send out
> requests with the same controller epoch until the old controller's
> handleNewSession() can execute in the controller lock.
> ControllerEpochListener does not seem necessary, so we can probably delete it.
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