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https://issues.apache.org/jira/browse/MAPREDUCE-4613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13445384#comment-13445384
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Arun C Murthy commented on MAPREDUCE-4613:
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What scheduler are you using? If you are using the default FifoScheduler,
you'll run into MAPREDUCE-4299 which isn't committed to hadoop-0.23.1.
> 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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