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https://issues.apache.org/jira/browse/MAPREDUCE-3268?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Harsh J updated MAPREDUCE-3268:
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Component/s: (was: mrv2)
> MR2 capacity scheduler doesn't spread tasks evenly on an underutilized cluster
> ------------------------------------------------------------------------------
>
> Key: MAPREDUCE-3268
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-3268
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: scheduler
> Affects Versions: 0.23.0
> Reporter: Todd Lipcon
>
> The fair scheduler in MR1 has the behavior that, if a job is submitted to an
> under-utilized cluster and the cluster has more open slots than tasks in the
> job, the tasks are spread evenly throughout the cluster. This improves job
> latency since more spindles and NICs are utilized to complete the job. In MR2
> I see this issue causing significantly longer job runtimes when there is
> excess capacity in the cluster -- especially on reducers which sometimmes end
> up clumping together on a smaller set of nodes which then become disk/network
> constrained.
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