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https://issues.apache.org/jira/browse/MAPREDUCE-1463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12835041#action_12835041
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Scott Chen commented on MAPREDUCE-1463:
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@Todd: That is a good point. If the reducer can later on catch up with the 
mapper, then there is no harm for the delay at the beginning. 

@Arun: I know you don't like this because it increases the complexity. Will you 
feel more comfortable if we move this just inside fairscheduler?

> 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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