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https://issues.apache.org/jira/browse/HBASE-6228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13401326#comment-13401326
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Jonathan Hsieh commented on HBASE-6228:
---------------------------------------

Is there anyway we can add tests to these subtle recovery fixes?  

Part of me says we should just take a something like lock on the region (in zk, 
possibly moving it into RIT) before we start fixing them up like this to make 
this obvious and to eliminate these classes of races.  
                
> 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
>
>
> 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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