[jira] [Resolved] (MAPREDUCE-1206) Need a better answer for "how many reduces?"

["Allen Wittenauer (Resolved) (JIRA)" <ji...@apache.org>]

     [ 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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