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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 Fri, 28 Oct 2011 23:09:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13138908#comment-13138908
] 

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

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

INLINE COMMENTS
  src/main/java/org/apache/hadoop/hbase/master/MasterFileSystem.java:223 Basically what Nicolas
said ... setting the abort flag here will not have any immediate effect.

  From HMaster code
    status.setStatus("Splitting logs after master startup");
      this.fileSystemManager.
    splitLogAfterStartup(this.serverManager.getOnlineServers().keySet());
    // Make sure root and meta assigned before proceeding.
    assignRootAndMeta(status);

  the master thread will try to assignRootAndMeta() even if splitLogAfterStartup() returns
with abort flag set. May be if HMaster.abort() had set the interrupt flag on at least the
main master thread then it might have worked ...

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
>
>
> 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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