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Date: Mon, 22 Feb 2010 21:02:27 +0000 (UTC)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Commented: (MAPREDUCE-1521) Protection against incorrectly
 configured reduces
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12836902#action_12836902 ] 

Todd Lipcon commented on MAPREDUCE-1521:
----------------------------------------

This makes me just a little bit nervous - the case I'm worried about is when a job is working fine in production and then starts failing at 3am some morning because the data volume increased just a little bit over the threshold.

Could we default this behavior off and only turn it on for clusters where the operators prefer it?

> 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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