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From "Jason Lowe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4358) Reducers are assigned containers before all maps are assigned containers
Date Wed, 20 Jun 2012 21:07:42 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13397868#comment-13397868

Jason Lowe commented on MAPREDUCE-4358:

The AM is supposed to be watching its headroom to see if it has enough resources for running
maps and will even preempt (kill) reduce tasks to make room for map tasks when there isn't
enough headroom.  Which scheduler is being used for this test?  If it's the FifoScheduler
then I believe this is a duplicate of MAPREDUCE-4299.  If the AM is being told an incorrectly
computed headroom then it could think there is sufficient room to allocate containers for
maps when in fact they've all been filled with reduce tasks.
> Reducers are assigned containers before all maps are assigned containers
> ------------------------------------------------------------------------
>                 Key: MAPREDUCE-4358
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4358
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 2.0.0-alpha
>            Reporter: Ahmed Radwan
> Reducers start to get containers before all maps are. We have seen this issue and it
is problematic since if there is no avaialable resources for the remaining maps, the job will
just stall where reducers are waiting for mappers which are unable to start because there
is no containers available.

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