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https://issues.apache.org/jira/browse/MAPREDUCE-1463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12919116#action_12919116
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Joydeep Sen Sarma commented on MAPREDUCE-1463:
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on a somewhat different note: i frequently see reducers not being scheduled (to
wait for map completions) even when the cluster has tons of idle reduce slots.
that makes no sense (especially when pre-emption is enabled). that seems to
suggest that some of the heuristics should take cluster load into account.
> Reducer should start faster for smaller jobs
> --------------------------------------------
>
> Key: MAPREDUCE-1463
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1463
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: jobtracker
> Reporter: Scott Chen
> Assignee: Scott Chen
> Attachments: MAPREDUCE-1463-v1.patch, MAPREDUCE-1463-v2.patch,
> MAPREDUCE-1463-v3.patch
>
>
> Our users often complain about the slowness of smaller ad-hoc jobs.
> The overhead to wait for the reducers to start in this case is significant.
> It will be good if we can start the reducer sooner in this case.
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