[MAPREDUCE-239] Attribute to mark Mappers and Reducers as side-effect free

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Assignee: Unassigned
• Reporter: Owen O'Malley
• Created: 05/Feb/07 22:59
• Updated: 16/Jan/12 08:58
• Resolved: 16/Jan/12 08:58

Description

There should be an annotation to mark Mapper and Reducer classes as side-effect free. This annotation could then be used to disable speculative execution for such classes. Furthermore, defining a class without the NoSideEffect attribute as a combiner would be a run-time error.

@NoSideEffects
class MyMapper extends MapReduceBase implements Mapper

{ ... }

would declare that MyMapper may be run speculatively.

@NoSideEffects
class MyReducer extends MapReduceBase implements Reducer

{ ...}

declares that MyReducer can be run speculative and as a combiner.