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From "Jimmy Xiang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8545) Meta stuck in transition when it is assigned to a just restarted dead region sever
Date Fri, 17 May 2013 22:51:16 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8545?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13661117#comment-13661117
] 

Jimmy Xiang commented on HBASE-8545:
------------------------------------

bq. When we return -1 out of zkassign, what will the caller do? Stop processing the assign?

Yes, the assignment processing is aborted on that region server, since it is not the server
meant to open the region per AM.

bq. Is this a bug fix?

Yes, that's an existing bug.  Once we tighten things up, this bug showed up. It is just a
testing issue though.
                
> Meta stuck in transition when it is assigned to a just restarted dead region sever 
> -----------------------------------------------------------------------------------
>
>                 Key: HBASE-8545
>                 URL: https://issues.apache.org/jira/browse/HBASE-8545
>             Project: HBase
>          Issue Type: Bug
>          Components: Region Assignment
>            Reporter: Jimmy Xiang
>            Assignee: Jimmy Xiang
>         Attachments: trunk-8545.patch, trunk-8545_v2.patch
>
>
> Support the meta region server is down, and the SSH tries to re-assign it.  This could
happen:
> 1. AM plans to assign meta to a region server (R_old);
> 2. Now R_old is dead, the new region server (R_new) starts up on the same host, port,
but gets a different start code;
> 3. AM sends the open region request to R_new and the Meta is opened on it;
> 4. AM gets ZK event, but it is from a different region server instance (R_new), not the
expected one (R_old), so it sends a close region request to R_new;
> 5. Now, the meta is stuck in transition and won't be assigned.
> This won't happen to a user region since the SSH for R_old will find out the user region
stuck in transition and re-assign it.  For meta, it is a little different.  AM checks if a
dead region server carries the meta based on the ZK info, which is changed to the new region
server R_new at step 3 by the open region handler.
> The fix I was thinking about is:
> 1. In checking if a region server carries a region, uses the region transition information
if it exists (which is the source of truth, to master), if not, checks the ZK data as before;
> 2. In open region handler, when transition assign zk node from offline to opening, make
sure the current region server is the expected one (ZK#transitionNode, existing code doesn't
check the target server name).

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