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From "Damien Hardy (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-5051) Combiner not used when NUM_REDUCES=0
Date Thu, 07 Mar 2013 17:20:13 GMT
Damien Hardy created MAPREDUCE-5051:
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             Summary: Combiner not used when NUM_REDUCES=0
                 Key: MAPREDUCE-5051
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5051
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: mrv1
    Affects Versions: 2.0.2-alpha
         Environment: CDH4.1.2 MR1
            Reporter: Damien Hardy


We have a M/R job that use Mapper + Combiner but have nothing to do in Reducer :
Bulk indexing of HBase data in ElasticSearch,
Map output is K / V : #bulk / json_data_to_be_indexed.

So job is launched maps work, combiners index and a reducer is created for nothing (sometimes
waiting for other M/R job to free a tasktracker slot for reducer cf. MAPREDUCE-5019 )

When we put ```job.setNumReduceTasks(0);``` in our job .run(), mapper are started but combiner
are not used.

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