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https://issues.apache.org/jira/browse/MAPREDUCE-3951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13584668#comment-13584668
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Todd Lipcon commented on MAPREDUCE-3951:
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Seems like so long as the schedulers we expect people to use support this
feature, we should be OK.
> Tasks are not evenly spread throughout cluster in MR2
> -----------------------------------------------------
>
> Key: MAPREDUCE-3951
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-3951
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: scheduler
> Affects Versions: 0.23.0, 0.24.0
> Reporter: Todd Lipcon
>
> In MR1 (at least with the fair and fifo schedulers), if you submit a job that
> needs fewer resources than the cluster can provide, the tasks are spread
> relatively evenly across the node. For example, submitting a 100-map job to a
> 50-node cluster, each with 10 slots, results in 2 tasks on each machine. In
> MR2, however, the tasks would pile up on the first 10 nodes of the cluster,
> leaving the other nodes unused. This is highly suboptimal for many use cases.
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