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