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https://issues.apache.org/jira/browse/MAPREDUCE-5051?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13596942#comment-13596942
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Damien Hardy commented on MAPREDUCE-5051:
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Hmm that is sad. it fit really well with our needs: Aggregating things by
mapper easily for bulk treatment that not really need global aggregation (like
indexation).
Can you point me out where this is done in the code (running or not Combiner
class) ?
> 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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