[MAPREDUCE-3520] Allow for metrics to be exchanged between maps and reduces

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.0.0-alpha
• Component/s: mrv2
• Assignee: Unassigned
• Reporter: Robert Joseph Evans
• Created: 08/Dec/11 16:13
• Updated: 10/Mar/15 04:32

Description

Some people on the mailing lists have requested having read access in reducers to counters that were set by mappers. I propose that we provide a new interface for doing this. The counter data in addition to being set periodically to the Application Master would be put into the intermediate output of the mapper for each reducer and be specially marked as such. When the reducers fetch that data they can combine it together and provide a read only interface to it.

This allows users to potentially optimize their code on the reducer side if they know some special metadata before hand.