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Date: Thu, 7 Mar 2013 19:20:13 +0000 (UTC)
From: "Robert Joseph Evans (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Message-ID: <JIRA.12635836.1362676702378.401982.1362684013945@arcas>
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Subject: [jira] [Resolved] (MAPREDUCE-5051) Combiner not used when
 NUM_REDUCES=0
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     [ https://issues.apache.org/jira/browse/MAPREDUCE-5051?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Robert Joseph Evans resolved MAPREDUCE-5051.
--------------------------------------------

    Resolution: Won't Fix

If you feel strongly that this should be supported you can reopen this JIRA as new feature work.
                
> 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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