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https://issues.apache.org/jira/browse/MAPREDUCE-2124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12919937#action_12919937
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Chris Douglas commented on MAPREDUCE-2124:
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bq. are you worried about memory or CPU? Doesn't one job-counter require only 
one object per job?

Memory. The counters are recorded per task

> Add job counters for measuring time spent in three different phases in 
> reducers
> -------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-2124
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2124
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: jobtracker
>    Affects Versions: 0.22.0
>            Reporter: Scott Chen
>            Assignee: Scott Chen
>            Priority: Minor
>             Fix For: 0.22.0
>
>
> We currently have SLOTS_MILLIS_REDUCES which measures the total slot time of 
> reducer.
> It will be useful if we have
> {code}
> SLOTS_MILLIS_REDUCES_COPY
> SLOTS_MILLIS_REDUCES_SORT
> SLOTS_MILLIS_REDUCES_REDUCE
> {code}
> which measures three different phases of a reducer.
> This will help us identify the bottleneck of the reducers.

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