[jira] [Assigned] (HBASE-5081) Distributed log splitting deleteNode races againsth splitLog retry

["Jimmy Xiang (Assigned) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-5081?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jimmy Xiang reassigned HBASE-5081:
----------------------------------

    Assignee: Prakash Khemani  (was: Jimmy Xiang)

Prakash is going to put up a patch to fix createIfAbsent, which is great alternative.
                
> Distributed log splitting deleteNode races againsth 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: 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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