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Date: Wed, 30 Nov 2011 06:41:40 +0000 (UTC)
From: "Ted Yu (Commented) (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HBASE-4899) Region would be assigned twice
 easily with continually  killing server and moving region in testing
 environment
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    [ https://issues.apache.org/jira/browse/HBASE-4899?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13159859#comment-13159859 ] 

Ted Yu commented on HBASE-4899:
-------------------------------

@Chunhui:
Please let us know testing result on your QA environment.
                
> Region would be assigned twice easily with continually  killing server and moving region in testing environment
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-4899
>                 URL: https://issues.apache.org/jira/browse/HBASE-4899
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.92.0
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>         Attachments: hbase-4899.patch
>
>
> Before assigning region in ServerShutdownHandler#process, it will check whether region is in RIT,
> however, this checking doesn't work as the excepted in the following case:
> 1.move region A from server B to server C
> 2.kill server B
> 3.start server B immediately
> Let's see what happen in the code for the above case
> {code}
> for step1:
> 1.1 server B close the region A,
> 1.2 master setOffline for region A,(AssignmentManager#setOffline:this.regions.remove(regionInfo))
> 1.3 server C start to open region A.(Not completed)
> for step3:
> master ServerShutdownHandler#process() for server B
> {
> ..
> splitlog()
> ...
> List<RegionState> regionsInTransition =
>         this.services.getAssignmentManager()
>         .processServerShutdown(this.serverName);
> ...
> Skip regions that were in transition unless CLOSING or PENDING_CLOSE
> ...
> assign region
> }
> {code}
> In fact, when running ServerShutdownHandler#process()#this.services.getAssignmentManager().processServerShutdown(this.serverName), region A is in RIT (step1.3 not completed), but the return List<RegionState> regionsInTransition doesn't contain it, because region A has removed from AssignmentManager.regions by AssignmentManager#setOffline in step 1.2
> Therefore, region A will be assigned twice.
> Actually, one server killed and started twice will also easily cause region assigned twice.
> Exclude the above reason, another probability : 
> when execute ServerShutdownHandler#process()#MetaReader.getServerUserRegions ,region is included which is in RIT now.
> But after completing MetaReader.getServerUserRegions, the region has been opened in other server and is not in RIT now.
> In our testing environment where balancing,moving and killing are executed periodly, assigning region twice often happens, and it is hateful because it will affect other test cases.

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