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https://issues.apache.org/jira/browse/KAFKA-841?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14311021#comment-14311021
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Jay Kreps commented on KAFKA-841:
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[~nehanarkhede] is this still a consideration?
> Merge the partition and replica state machines into a single unified state
> machine in the controller
> ----------------------------------------------------------------------------------------------------
>
> Key: KAFKA-841
> URL: https://issues.apache.org/jira/browse/KAFKA-841
> Project: Kafka
> Issue Type: Improvement
> Components: controller
> Affects Versions: 0.8.1
> Reporter: Neha Narkhede
> Assignee: Neha Narkhede
>
> After using the controller for a while as part of 0.8, I think it might be
> worth looking into merging the separate state machines into a single unified
> one. The reason is most events end up invoking state transitions on both
> partitions and replicas. Initially, the thought of separating the two was to
> handle cases which only touch one state machine (for example, changing the
> replication factor or changing the number of partitions online). However,
> these features also would end up touching both state machines. The complexity
> comes from the correct ordering that one has to ensure between the operations
> on both these state machines (KAFKA-831). Due to this, some state transitions
> are unable to batch RPCs and/or zookeeper writes/reads since they need to
> happen in each of the state machines separately. Since this will
> significantly change controller code, I'm filing this for 0.8.1
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