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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2312) Possible data loss when RS goes into GC pause while rolling HLog
Date Tue, 16 Mar 2010 22:16:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12846169#action_12846169
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Todd Lipcon commented on HBASE-2312:
------------------------------------

Having slept on it, I think the log chasing described above is actually avoidable. A couple
different thoughts:

a) as above, I think we could be careful about using listStatus() to see whether the RS makes
any progress
b) perhaps a very simple solution is to have the regionserver call ZK's sync() method before
initiating metadata ops. This will limit the RS to a single metadata transition after it has
been declared dead. This should be a useful pattern throughput HBase.



> 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: Hadoop HBase
>          Issue Type: Bug
>          Components: master, regionserver
>    Affects Versions: 0.20.3
>            Reporter: Karthik Ranganathan
>
> 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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