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https://issues.apache.org/jira/browse/HBASE-5081?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13180174#comment-13180174
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Zhihong Yu commented on HBASE-5081:
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@Prakash:
Thanks for your sharp eyes. I will upload another patch when I get back home.
> Distributed log splitting deleteNode races against splitLog retry
> ------------------------------------------------------------------
>
> Key: HBASE-5081
> URL: https://issues.apache.org/jira/browse/HBASE-5081
> Project: HBase
> Issue Type: Bug
> Components: wal
> Affects Versions: 0.92.0, 0.94.0
> Reporter: Jimmy Xiang
> Assignee: Prakash Khemani
> Fix For: 0.92.0
>
> Attachments:
> 0001-HBASE-5081-jira-Distributed-log-splitting-deleteNode.patch,
> 0001-HBASE-5081-jira-Distributed-log-splitting-deleteNode.patch,
> 0001-HBASE-5081-jira-Distributed-log-splitting-deleteNode.patch,
> 0001-HBASE-5081-jira-Distributed-log-splitting-deleteNode.patch,
> 0001-HBASE-5081-jira-Distributed-log-splitting-deleteNode.patch,
> 0001-HBASE-5081-jira-Distributed-log-splitting-deleteNode.patch,
> 5081-deleteNode-with-while-loop.txt,
> distributed-log-splitting-screenshot.png, hbase-5081-patch-v6.txt,
> hbase-5081-patch-v7.txt, hbase-5081_patch_for_92_v4.txt,
> hbase-5081_patch_v5.txt, patch_for_92.txt, patch_for_92_v2.txt,
> patch_for_92_v3.txt
>
>
> Recently, during 0.92 rc testing, we found distributed log splitting hangs
> there forever. Please see attached screen shot.
> I looked into it and here is what happened I think:
> 1. One rs died, the servershutdownhandler found it out and started the
> distributed log splitting;
> 2. All three tasks failed, so the three tasks were deleted, asynchronously;
> 3. Servershutdownhandler retried the log splitting;
> 4. During the retrial, it created these three tasks again, and put them in a
> hashmap (tasks);
> 5. The asynchronously deletion in step 2 finally happened for one task, in
> the callback, it removed one
> task in the hashmap;
> 6. One of the newly submitted tasks' zookeeper watcher found out that task is
> unassigned, and it is not
> in the hashmap, so it created a new orphan task.
> 7. All three tasks failed, but that task created in step 6 is an orphan so
> the batch.err counter was one short,
> so the log splitting hangs there and keeps waiting for the last task to
> finish which is never going to happen.
> So I think the problem is step 2. The fix is to make deletion sync, instead
> of async, so that the retry will have
> a clean start.
> Async deleteNode will mess up with split log retrial. In extreme situation,
> if async deleteNode doesn't happen
> soon enough, some node created during the retrial could be deleted.
> deleteNode should be sync.
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