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From "bluedavy (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3872) Hole in split transaction rollback; edits to .META. need to be rolled back even if it seems like they didn't make it
Date Sun, 09 Oct 2011 12:08:30 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13123670#comment-13123670
] 

bluedavy commented on HBASE-3872:
---------------------------------

@stack
current patch will cause data-loss in this situation:
1. change the SplitTransaction just like @mingjian said;
2. then create a table & put some data in hbase shell;
3. split the table in hbase shell;
4. kill the region server hosted the table;
5. after master do servershutdownhandler,then the table can be wrote again,but the data previous
wrote to the table lost.

and in above code,if we don't kill the region server,then the parent region cann't be wrote,even
if restart the cluster.
                
> Hole in split transaction rollback; edits to .META. need to be rolled back even if it
seems like they didn't make it
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-3872
>                 URL: https://issues.apache.org/jira/browse/HBASE-3872
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.90.3
>            Reporter: stack
>            Assignee: stack
>            Priority: Blocker
>             Fix For: 0.90.4
>
>         Attachments: 3872-v2.txt, 3872.txt
>
>
> Saw this interesting one on a cluster of ours.  The cluster was configured with too few
handlers so lots of the phenomeneon where actions were queued but then by the time they got
into the server and tried respond to the client, the client had disconnected because of the
timeout of 60 seconds.  Well, the meta edits for a split were queued at the regionserver carrying
.META. and by the time it went to write back, the client had gone (the first insert of parent
offline with daughter regions added as info:splitA and info:splitB).  The client presumed
the edits failed and 'successfully' rolled back the transaction (failing to undo .META. edits
thinking they didn't go through).
> A few minutes later the .META. scanner on master runs.  It sees 'no references' in daughters
-- the daughters had been cleaned up as part of the split transaction rollback -- so it thinks
its safe to delete the parent.
> Two things:
> + Tighten up check in master... need to check daughter region at least exists and possibly
the daughter region has an entry in .META.
> + Dependent on the edit that fails, schedule rollback edits though it will seem like
they didn't go through.
> This is pretty critical one.

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