[MAPREDUCE-4864] Adding new umbilical protocol RPC, "getAggregationTargets()", for node-level combiner.

• Type: Sub-task
• Status: In Progress
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.0.0-alpha1
• Component/s: applicationmaster, mrv2, tasktracker
• Assignee: Tsuyoshi Ozawa
• Reporter: Tsuyoshi Ozawa
• Created: 10/Dec/12 05:23
• Updated: 12/May/16 18:22

Description

MapTasks need to know whether or not they should start node-level combiner agaist outputs of mapper on their node.

The new umbilical RPC, getAggregationTargets(), is used to get outputs to be aggregated on the node. The definition as follows:

AggregationTarget getAggregationTargets(TaskAttemptID aggregator) throws IOException;

AggregationTarget is a abstraction class of array of TaskAttemptID to be aggregated.