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From "Allen Wittenauer (Resolved) (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (MAPREDUCE-1206) Need a better answer for "how many reduces?"
Date Wed, 02 Nov 2011 17:47:33 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-1206?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Allen Wittenauer resolved MAPREDUCE-1206.

    Resolution: Won't Fix
> Need a better answer for "how many reduces?"
> --------------------------------------------
>                 Key: MAPREDUCE-1206
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1206
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Allen Wittenauer
> http://hadoop.apache.org/common/docs/current/mapred_tutorial.html#Reducer
> --snip--
> How Many Reduces?
> The right number of reduces seems to be 0.95 or 1.75 multiplied by (<no. of nodes>
* mapred.tasktracker.reduce.tasks.maximum).
> --snip--
> Sure, if you only ever run one job on your grid.  There should really be a better answer
here, especially explaining what the impact is of a high/low number when chaining multiple
map/reduce jobs.

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