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From "Chris Douglas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2771) changing the number of reduces dramatically changes the time of the map time
Date Fri, 01 Aug 2008 22:33:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12619154#action_12619154
] 

Chris Douglas commented on HADOOP-2771:
---------------------------------------

Does this job run with a combiner? That would also add time spent in each spill.

> changing the number of reduces dramatically changes the time of the map time
> ----------------------------------------------------------------------------
>
>                 Key: HADOOP-2771
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2771
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.17.1
>            Reporter: Owen O'Malley
>
> By changing the number of reduces, the time for an individual map changes radically.
By running the same program and data with different numbers of reduces (2500, 7500, 25000)
the times for each map changed radically (0:50, 1:20, 5h).

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