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https://issues.apache.org/jira/browse/HBASE-4729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13159311#comment-13159311
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stack commented on HBASE-4729:
------------------------------

bq. For unexpected zk exception, we should abort the master instead of logging 
error.

It does.  It falls through to the abort call.

I'll make issue for SessionExpiredException.

I'll fix missing test category on commit.

But thinking more on this patch, it works for the altering case but I don't 
think it will work for the issue I reported where we are unassigning because 
region is being moved by balancer.   The unassign looks like it moved so we'll 
go ahead and try open region in new location.  The splitting code may fix it up 
but need to check.
                
> Race between online altering and splitting kills the master
> -----------------------------------------------------------
>
>                 Key: HBASE-4729
>                 URL: https://issues.apache.org/jira/browse/HBASE-4729
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.92.0
>            Reporter: Jean-Daniel Cryans
>            Assignee: ramkrishna.s.vasudevan
>            Priority: Critical
>             Fix For: 0.92.0, 0.94.0
>
>         Attachments: 4729-v2.txt, 4729-v3.txt, 4729-v4.txt, 4729.txt
>
>
> I was running an online alter while regions were splitting, and suddenly the 
> master died and left my table half-altered (haven't restarted the master yet).
> What killed the master:
> {quote}
> 2011-11-02 17:06:44,428 FATAL org.apache.hadoop.hbase.master.HMaster: 
> Unexpected ZK exception creating node CLOSING
> org.apache.zookeeper.KeeperException$NodeExistsException: KeeperErrorCode = 
> NodeExists for /hbase/unassigned/f7e1783e65ea8d621a4bc96ad310f101
>         at 
> org.apache.zookeeper.KeeperException.create(KeeperException.java:110)
>         at 
> org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
>         at org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:637)
>         at 
> org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper.createNonSequential(RecoverableZooKeeper.java:459)
>         at 
> org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper.create(RecoverableZooKeeper.java:441)
>         at 
> org.apache.hadoop.hbase.zookeeper.ZKUtil.createAndWatch(ZKUtil.java:769)
>         at 
> org.apache.hadoop.hbase.zookeeper.ZKAssign.createNodeClosing(ZKAssign.java:568)
>         at 
> org.apache.hadoop.hbase.master.AssignmentManager.unassign(AssignmentManager.java:1722)
>         at 
> org.apache.hadoop.hbase.master.AssignmentManager.unassign(AssignmentManager.java:1661)
>         at org.apache.hadoop.hbase.master.BulkReOpen$1.run(BulkReOpen.java:69)
>         at 
> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
>         at 
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
>         at java.lang.Thread.run(Thread.java:662)
> {quote}
> A znode was created because the region server was splitting the region 4 
> seconds before:
> {quote}
> 2011-11-02 17:06:40,704 INFO 
> org.apache.hadoop.hbase.regionserver.SplitTransaction: Starting split of 
> region TestTable,0012469153,1320253135043.f7e1783e65ea8d621a4bc96ad310f101.
> 2011-11-02 17:06:40,704 DEBUG 
> org.apache.hadoop.hbase.regionserver.SplitTransaction: 
> regionserver:62023-0x132f043bbde0710 Creating ephemeral node for 
> f7e1783e65ea8d621a4bc96ad310f101 in SPLITTING state
> 2011-11-02 17:06:40,751 DEBUG org.apache.hadoop.hbase.zookeeper.ZKAssign: 
> regionserver:62023-0x132f043bbde0710 Attempting to transition node 
> f7e1783e65ea8d621a4bc96ad310f101 from RS_ZK_REGION_SPLITTING to 
> RS_ZK_REGION_SPLITTING
> ...
> 2011-11-02 17:06:44,061 DEBUG org.apache.hadoop.hbase.zookeeper.ZKAssign: 
> regionserver:62023-0x132f043bbde0710 Successfully transitioned node 
> f7e1783e65ea8d621a4bc96ad310f101 from RS_ZK_REGION_SPLITTING to 
> RS_ZK_REGION_SPLIT
> 2011-11-02 17:06:44,061 INFO 
> org.apache.hadoop.hbase.regionserver.SplitTransaction: Still waiting on the 
> master to process the split for f7e1783e65ea8d621a4bc96ad310f101
> {quote}
> Now that the master is dead the region server is spewing those last two lines 
> like mad.

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