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https://issues.apache.org/jira/browse/KAFKA-3083?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15107770#comment-15107770
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Mayuresh Gharat commented on KAFKA-3083:
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However, the replica would be in the cache of the controller B, so would it be
elected in this case? Would it be an actual problem if the B is demoted and
another controller comes up?
---> That seems right, it should be in the cache of controller B and should be
elected as leader. If however B goes down before this and a new controller is
elected, it will read the data from zookeeper and might not be able to elect a
new leader if uncleanLeaderElection is turned OFF.
> a soft failure in controller may leave a topic partition in an inconsistent
> state
> ---------------------------------------------------------------------------------
>
> Key: KAFKA-3083
> URL: https://issues.apache.org/jira/browse/KAFKA-3083
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 0.9.0.0
> Reporter: Jun Rao
> Assignee: Mayuresh Gharat
>
> The following sequence can happen.
> 1. Broker A is the controller and is in the middle of processing a broker
> change event. As part of this process, let's say it's about to shrink the isr
> of a partition.
> 2. Then broker A's session expires and broker B takes over as the new
> controller. Broker B sends the initial leaderAndIsr request to all brokers.
> 3. Broker A continues by shrinking the isr of the partition in ZK and sends
> the new leaderAndIsr request to the broker (say C) that leads the partition.
> Broker C will reject this leaderAndIsr since the request comes from a
> controller with an older epoch. Now we could be in a situation that Broker C
> thinks the isr has all replicas, but the isr stored in ZK is different.
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