Hadoop Map/Reduce
  1. Hadoop Map/Reduce
  2. MAPREDUCE-1206

Need a better answer for "how many reduces?"

    Details

    • Type: Bug Bug
    • Status: Resolved
    • Priority: Major Major
    • Resolution: Won't Fix
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: None
    • Labels:
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      Description

      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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          • Assignee:
            Unassigned
            Reporter:
            Allen Wittenauer
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