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https://issues.apache.org/jira/browse/HBASE-4729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13159416#comment-13159416
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stack commented on HBASE-4729:
------------------------------
Now I think we should commit this.
My concern about a failed unassign as part of a balance is unfounded. Balances
work by running unassign and then in the ClosedRegionHandler we'll do the
assign elsewhere. The latter assign will not happen if the unassign/close
doesn't complete because of a concurrent SPLITTING/SPLIT.
Regards the TODO on what to do on rollback of a failed split, again, we should
be ok in the balancing case; the cluster will be out-of-balance if parent comes
back on line after our failed unassign attempt but so what. It'll be fixed
next time the balancer runs.
On SessionExpiredException handling, that should be done in one place only
rather than spread about the codebase (We need to refactor RecoverableZooKeeper
so that it will create new ZooKeeper to retry on SessionExpiredException).
Chatting with J-D, I should rename this issue since the focus has become
balance+concurrent split; the alter case is less critical since we do not have
online alter enabled by default (this patch will help some but more work to do
-- I'll open new issue).
> 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-v5.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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