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Posted to mapreduce-issues@hadoop.apache.org by "Arun C Murthy (JIRA)" <ji...@apache.org> on 2012/08/31 00:54:07 UTC

[jira] [Commented] (MAPREDUCE-4613) Scheduling of reduce tasks results in starvation

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13445384#comment-13445384 ] 

Arun C Murthy commented on MAPREDUCE-4613:
------------------------------------------

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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