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https://issues.apache.org/jira/browse/HBASE-4729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13159113#comment-13159113
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Ted Yu commented on HBASE-4729:
-------------------------------

{code}
+   * Updates the RegionState and sends the CLOSE RPC unless regions is being
{code}
The above should read '... region is being'
{code}
+   * of existence). TODO: What to do if split fails and is rolled back and
+   * parent is revivified?
{code}
The above would be handled in another JIRA. How about introducing a new state, 
such as RS_ZK_PARENT_REGION_CLOSE_THRU_SPLIT, so that rolling back failed split 
can decide what to do ?
{code}
+            } catch (KeeperException ke) {
+              LOG.warn("Presuming failed getData on " + path + "; presuming " +
+                "split and that the region to unassign, " + encodedName +
+                ", no longer exists -- confirm", ke);
+              return;
+            }
{code}
We should verify the above assumption by checking that ke is NoNodeException. 
If ke is not NoNodeException, we should abort.
                
> 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.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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