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From "Hong Tang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1521) Protection against incorrectly configured reduces
Date Tue, 23 Feb 2010 01:01:31 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12837019#action_12837019

Hong Tang commented on MAPREDUCE-1521:

We need to limit the amount of map output bytes or reduce input bytes as they must fit on
a single physical node. We could then fail the *job* if a particular map or reduce violates
such limits - assuming that reexecuting the map/reduce would lead to the same kind of violation.

> 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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