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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1838) DistRaid map tasks have large variance in running times
Date Fri, 29 Oct 2010 02:07:04 GMT

    [ 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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