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From "Vasco (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4613) Scheduling of reduce tasks results in starvation
Date Thu, 30 Aug 2012 21:30:07 GMT
Vasco created MAPREDUCE-4613:
--------------------------------

             Summary: Scheduling of reduce tasks results in starvation
                 Key: MAPREDUCE-4613
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4613
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: scheduler
    Affects Versions: 0.23.1
         Environment: 16 machine cluster
            Reporter: Vasco


If a job has more reduce tasks than there are containers available, then the reduce tasks
can occupy all containers causing starvation.

I understand that the correct behaviour when all containers are taken by reducers while mappers
are still pending, is for the running reducers to be "pre-empted". However, pre-emption does
not occur.

A work-around is to set the number of reducers < available containers.

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