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https://issues.apache.org/jira/browse/HBASE-6228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13403908#comment-13403908
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ramkrishna.s.vasudevan commented on HBASE-6228:
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@Chunhui
We are able to reproduce the double assignment scenario between SSH and master 
restart.
So i think we should have synchronized block or as Jon says we need some lock 
mechanism but that may be a bigger task.


                
> Fixup daughters twice  cause daughter region assigned twice
> -----------------------------------------------------------
>
>                 Key: HBASE-6228
>                 URL: https://issues.apache.org/jira/browse/HBASE-6228
>             Project: HBase
>          Issue Type: Bug
>          Components: master
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>             Fix For: 0.96.0
>
>         Attachments: HBASE-6228.patch, HBASE-6228v2.patch, 
> HBASE-6228v2.patch, HBASE-6228v3.patch, HBASE-6228v4.patch
>
>
> First, how fixup daughters twice happen?
> 1.we will fixupDaughters at the last of HMaster#finishInitialization
> 2.ServerShutdownHandler will fixupDaughters when reassigning region through 
> ServerShutdownHandler#processDeadRegion
> When fixupDaughters, we will added daughters to .META., but it coudn't 
> prevent the above case, because FindDaughterVisitor.
> The detail is as the following:
> Suppose region A is a splitted parent region, and its daughter region B is 
> missing
> 1.First, ServerShutdownHander thread fixup daughter, so add daughter region B 
> to .META. with serverName=null, and assign the daughter.
> 2.Then, Master's initialization thread will also find the daughter region B 
> is missing and assign it. It is because FindDaughterVisitor consider daughter 
> is missing if its serverName=null

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