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https://issues.apache.org/jira/browse/MAPREDUCE-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12836765#action_12836765
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Luke Lu commented on MAPREDUCE-1521:
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2a. Track output bytes per map and compute an extrapolated mapOutputBytes from 
a few randomly selected map output, so only a few maps needs to complete. We 
can have an expert mode to bypass the heuristic.

> Protection against incorrectly configured reduces
> -------------------------------------------------
>
>                 Key: MAPREDUCE-1521
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1521
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: jobtracker
>            Reporter: Arun C Murthy
>            Assignee: Arun C Murthy
>            Priority: Critical
>             Fix For: 0.22.0
>
>
> We've seen a fair number of instances where naive users process huge 
> data-sets (>10TB) with badly mis-configured #reduces e.g. 1 reduce.
> This is a significant problem on large clusters since it takes each attempt 
> of the reduce a long time to shuffle and then run into problems such as local 
> disk-space etc. Then it takes 4 such attempts.
> Proposal: Come up with heuristics/configs to fail such jobs early. 
> Thoughts?

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