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Date: Thu, 28 Oct 2010 22:07:04 -0400 (EDT)
From: "Hudson (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Commented: (MAPREDUCE-1838) DistRaid map tasks have large
 variance in running times
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-1838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12926145#action_12926145 ] 

Hudson commented on MAPREDUCE-1838:
-----------------------------------

Integrated in Hadoop-Mapreduce-trunk-Commit #523 (See [https://hudson.apache.org/hudson/job/Hadoop-Mapreduce-trunk-Commit/523/])
    

> DistRaid map tasks have large variance in running times
> -------------------------------------------------------
>
>                 Key: MAPREDUCE-1838
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1838
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: contrib/raid
>    Affects Versions: 0.20.1
>            Reporter: Ramkumar Vadali
>            Assignee: Ramkumar Vadali
>            Priority: Minor
>             Fix For: 0.22.0
>
>         Attachments: MAPREDUCE-1838.patch
>
>
> HDFS RAID uses map-reduce jobs to generate parity files for a set of source files. Each map task gets a subset of files to operate on. The current code assigns files by walking through the list of files given in the constructor of DistRaid
> The problem is that the list of files given to the constructor has the order of (pretty much) the directory listing. When a large number of files is added, files in that order tend to have the same size. Thus a map task can end up with large files where as another can end up with small files, increasing the variance in run times.
> We could do smarter assignment by using the file sizes.

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