[MAPREDUCE-5051] Combiner not used when NUM_REDUCES=0

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 2.0.2-alpha
• Component/s: mrv1

Environment

CDH4.1.2 MR1

• Assignee: Unassigned
• Reporter: Damien Hardy
• Created: 07/Mar/13 17:18
• Updated: 08/Mar/13 19:03
• Resolved: 07/Mar/13 19:18

Description

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.