[jira] [Created] (MAPREDUCE-3268) MR2 capacity scheduler doesn't spread tasks evenly on an underutilized cluster

["Todd Lipcon (Created) (JIRA)" <ji...@apache.org>]

MR2 capacity scheduler doesn't spread tasks evenly on an underutilized cluster
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                 Key: MAPREDUCE-3268
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3268
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: mrv2, 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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