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From "Karthik Ranganathan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-2312) Possible data loss when RS goes into GC pause while rolling HLog
Date Fri, 12 Mar 2010 01:21:27 GMT
Possible data loss when RS goes into GC pause while rolling HLog
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                 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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