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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-873) Simplify Job Recovery
Date Fri, 14 Aug 2009 12:49:14 GMT
Simplify Job Recovery

                 Key: MAPREDUCE-873
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-873
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: jobtracker
    Affects Versions: 0.20.1
            Reporter: Devaraj Das
            Assignee: Sharad Agarwal
             Fix For: 0.21.0

On a couple of occasions we have seen the JobTracker not being able to handle job recovery
well, and leading to cluster downtime after a restart. The current design for handling job
recovery is complex and prone to corner cases not being handled well enough. In retrospect,
it seems like the transaction log based approach as was proposed on HADOOP-3245 (http://tinyurl.com/luh9hb),
would have been a better/simpler model. However, that is a big project, and it seems for the
medium term, just handling job re-submissions after a restart is a good tradeoff. That is,
the JobTracker after getting restarted, will resubmit all jobs that were running in its past
life. They will all start from the beginning (downside is completed tasks will reexecute).
In the long term, the transaction log model or some variant of that should be pursued.

Thoughts/comments welcome.

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