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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