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https://issues.apache.org/jira/browse/MAPREDUCE-1129?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12768500#action_12768500
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Allen Wittenauer commented on MAPREDUCE-1129:
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We're seeing exactly the same issue.
> Assign multiple Map and Reduce tasks in Fairscheduler
> -----------------------------------------------------
>
> Key: MAPREDUCE-1129
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1129
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: contrib/fair-share
> Affects Versions: 0.20.1
> Reporter: Scott Chen
>
> In Hadoop-0.20, the period of heartbeat becomes much longer.
> Fairscheduler assigns at most one Map and one Reduce task per heartbeat.
> This makes the cluster become very inefficient. Often time only half of the
> slots are used.
> One idea is that we make Fairscheduler detect this situation (cluster under
> used) and scheduler more tasks in a heartbeat.
> Thoughts?
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