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From "Aaron Kimball (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 Thu, 23 Jun 2011 18:11:47 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054009#comment-13054009

Aaron Kimball commented on HBASE-3872:


I'm still working on getting more log data available. Hopefully I can get you more info. Here's
something interesting: I believe the parent regions are still hanging around in HBase regionservers.

hbck reports:

ERROR: Region UNKNOWN_REGION on <regionserver-redacted>:60020, key=4f424608930f7b3ae7c05c49e2bac2c1,
not on HDFS or in META but deployed on <regionserver-redacted>:60020
ERROR: Region UNKNOWN_REGION on <regionserver-redacted>:60020, key=81c5fb35e10f8ef61da78bbba28db7f9,
not on HDFS or in META but deployed on <regionserver-redacted>:60020

The region keys match those of the split parents which were abandoned when the "successful"
rollback didn't restore the parent entries in {{.META.}}. Is there a way to force these back
to storefiles on disk, and then manually add them to {{.META.}}?

> 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.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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