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