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From "Aaron Kimball (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1059) distcp can generate uneven map task assignments
Date Mon, 21 Dec 2009 22:51:18 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1059?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12793401#action_12793401
] 

Aaron Kimball commented on MAPREDUCE-1059:
------------------------------------------

Failing contrib tests are streaming regressions. No new unit tests for this patch because
it is a small patch and testing this behavior with unit tests would be challenging. A functional
test plan was outlined in my previous comment. 

> distcp can generate uneven map task assignments
> -----------------------------------------------
>
>                 Key: MAPREDUCE-1059
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1059
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: distcp
>            Reporter: Aaron Kimball
>            Assignee: Aaron Kimball
>         Attachments: MAPREDUCE-1059.2.patch, MAPREDUCE-1059.3.patch, MAPREDUCE-1059.patch
>
>
> distcp writes out a SequenceFile containing the source files to transfer, and their sizes.
Map tasks are created over spans of this file, representing files which each mapper should
transfer. In practice, some transfer loads yield many empty map tasks and a few tasks perform
the bulk of the work.

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