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https://issues.apache.org/jira/browse/HBASE-6228?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13406753#comment-13406753
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stack commented on HBASE-6228:
------------------------------

For example, on study:

+ RegionState is unreliable figuring state of region in master's memory; you 
cannot rely on it to answer the bigger question of who a region belongs to: 
master or regionserver.
+ In assign, we are careful with retries.  We actually need to be more careful 
especially around things like socket timeout (see Maryann's recent issue).  
Bulk assign does none of these checks.  Bulk assign was introduced originally 
to do assigns on cluster start; if anything failed, contract was we'd just 
crash out and restart cluster over.  That was how it was originally.  Now bulk 
assign is used all over -- e.g. in SSH -- in spite of its being loosey-goosey 
around failures.
                
> 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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