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https://issues.apache.org/jira/browse/KAFKA-2017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14982071#comment-14982071
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Onur Karaman commented on KAFKA-2017:
-------------------------------------

Thanks for the patch! I'm still looking through GroupMetadataManager.scala.

Regarding the schema evolution: what was the reason for making v1 represent 
offset schema and v2 represent group schema? I think we did a similar pattern 
for OffsetFetchRequest and OffsetCommitRequest (where one version represented 
commits to zookeeper and another represented commits to kafka), but I think 
circumstances were different in that kafka-based offset storage was meant to 
replace zookeeper-based offset storage.

> Persist Coordinator State for Coordinator Failover
> --------------------------------------------------
>
>                 Key: KAFKA-2017
>                 URL: https://issues.apache.org/jira/browse/KAFKA-2017
>             Project: Kafka
>          Issue Type: Sub-task
>          Components: consumer
>    Affects Versions: 0.9.0.0
>            Reporter: Onur Karaman
>            Assignee: Guozhang Wang
>            Priority: Blocker
>             Fix For: 0.9.0.0
>
>         Attachments: KAFKA-2017.patch, KAFKA-2017_2015-05-20_09:13:39.patch, 
> KAFKA-2017_2015-05-21_19:02:47.patch
>
>
> When a coordinator fails, the group membership protocol tries to failover to 
> a new coordinator without forcing all the consumers rejoin their groups. This 
> is possible if the coordinator persists its state so that the state can be 
> transferred during coordinator failover. This state consists of most of the 
> information in GroupRegistry and ConsumerRegistry.



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