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From "Phabricator (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-2312) Possible data loss when RS goes into GC pause while rolling HLog
Date Wed, 02 Nov 2011 05:34:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13141936#comment-13141936
] 

Phabricator commented on HBASE-2312:
------------------------------------

khemani has accepted the revision "HBASE-2312 [jira] Possible data loss when RS goes into
GC pause while rolling HLog".

  Looks good to me.

INLINE COMMENTS
  src/main/java/org/apache/hadoop/hbase/master/MasterFileSystem.java:201-205 In the original
patch the -splitting wouldn't be stripped off over here.  With the current diff, a region-server
which was earlier known to be dead will get another opportunity to be treated as alive. But
I don't think that will happen and this is fine.

REVISION DETAIL
  https://reviews.facebook.net/D99

                
> Possible data loss when RS goes into GC pause while rolling HLog
> ----------------------------------------------------------------
>
>                 Key: HBASE-2312
>                 URL: https://issues.apache.org/jira/browse/HBASE-2312
>             Project: HBase
>          Issue Type: Bug
>          Components: master, regionserver
>    Affects Versions: 0.90.0
>            Reporter: Karthik Ranganathan
>            Assignee: Nicolas Spiegelberg
>            Priority: Critical
>             Fix For: 0.92.0
>
>         Attachments: D99.1.patch, D99.2.patch, D99.3.patch
>
>
> There is a very corner case when bad things could happen(ie data loss):
> 1)	RS #1 is going to roll its HLog - not yet created the new one, old one will get no
more writes
> 2)	RS #1 enters GC Pause of Death
> 3)	Master lists HLog files of RS#1 that is has to split as RS#1 is dead, starts splitting
> 4)	RS #1 wakes up, created the new HLog (previous one was rolled) and appends an edit
- which is lost
> The following seems like a possible solution:
> 1)	Master detects RS#1 is dead
> 2)	The master renames the /hbase/.logs/<regionserver name>  directory to something
else (say /hbase/.logs/<regionserver name>-dead)
> 3)	Add mkdir support (as opposed to mkdirs) to HDFS - so that a file create fails if
the directory doesn't exist. Dhruba tells me this is very doable.
> 4)	RS#1 comes back up and is not able create the new hlog. It restarts itself.

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