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From "stack (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 Mon, 12 Sep 2011 22:35:09 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13103135#comment-13103135
] 

stack commented on HBASE-3872:
------------------------------

This patch plugged this hole two ways:

1. not removing parent region unless the daughter region existed
2. on split transaction failure, do NOT remove daughter regions; crash out the regionserver
and let fix up of the shutdown server do the fixup in meta adding daughters.

#1 in the above created HBASE-4238 where we won't delete parents if daughters that have themselves
split get cleaned up before their parent has all its references let go.  So #1 is being undone
over in the fix for HBASE-4238 since its possible daughter regions may not exist in the fs
legitimately.

> 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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