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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5211) Reducer intermediate files can collide during merge
Date Tue, 07 May 2013 01:29:16 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5211?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13650349#comment-13650349
] 

Hadoop QA commented on MAPREDUCE-5211:
--------------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12581974/MAPREDUCE-5211.branch-0.23.patch
  against trunk revision .

    {color:red}-1 patch{color}.  The patch command could not apply the patch.

Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/3574//console

This message is automatically generated.
                
> Reducer intermediate files can collide during merge
> ---------------------------------------------------
>
>                 Key: MAPREDUCE-5211
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5211
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 0.23.7
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>            Priority: Critical
>         Attachments: MAPREDUCE-5211.branch-0.23.patch
>
>
> The OnDiskMerger.merge method constructs an output path that is not unique to a reduce
attempt, and as a result can result in a file collision with other reducers from the same
app that are running on the same node.  In addition the name of the output file is based on
MapOutput.toString which may not be unique in light of multi-pass merges on disk since the
mapId will be null and the basename ends up as "MapOutput(null, DISK)"

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