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https://issues.apache.org/jira/browse/HBASE-20634?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16498698#comment-16498698
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Umesh Agashe commented on HBASE-20634:
--------------------------------------

+1 lgtm

> Reopen region while server crash can cause the procedure to be stuck
> --------------------------------------------------------------------
>
>                 Key: HBASE-20634
>                 URL: https://issues.apache.org/jira/browse/HBASE-20634
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Duo Zhang
>            Assignee: stack
>            Priority: Critical
>             Fix For: 3.0.0, 2.1.0, 2.0.1
>
>         Attachments: HBASE-20634-UT.patch, HBASE-20634.branch-2.0.001.patch, 
> HBASE-20634.branch-2.0.002.patch, HBASE-20634.branch-2.0.003.patch, 
> HBASE-20634.branch-2.0.004.patch, HBASE-20634.branch-2.0.005.patch, 
> HBASE-20634.branch-2.0.006.patch, HBASE-20634.branch-2.0.006.patch, 
> HBASE-20634.branch-2.0.007.patch
>
>
> Found this when implementing HBASE-20424, where we will transit the peer sync 
> replication state while there is server crash.
> The problem is that, in ServerCrashAssign, we do not have the region lock, so 
> it is possible that after we call handleRIT to clear the existing 
> assign/unassign procedures related to this rs, and before we schedule the 
> assign procedures, it is possible that that we schedule a unassign procedure 
> for a region on the crashed rs. This procedure will not receive the 
> ServerCrashException, instead, in addToRemoteDispatcher, it will find that it 
> can not dispatch the remote call and then a  FailedRemoteDispatchException 
> will be raised. But we do not treat this exception the same with 
> ServerCrashException, instead, we will try to expire the rs. Obviously the rs 
> has already been marked as expired, so this is almost a no-op. Then the 
> procedure will be stuck there for ever.
> A possible way to fix it is to treat FailedRemoteDispatchException the same 
> with ServerCrashException, as it will be created in addToRemoteDispatcher 
> only, and the only reason we can not dispatch a remote call is that the rs 
> has already been dead. The nodeMap is a ConcurrentMap so I think we could use 
> it as a guard.



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