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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