Tsuyoshi OZAWA created MAPREDUCE-4863:
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Summary: Adding aggregationWaitMap for node-level combiner.
Key: MAPREDUCE-4863
URL: https://issues.apache.org/jira/browse/MAPREDUCE-4863
Project: Hadoop Map/Reduce
Issue Type: Sub-task
Components: applicationmaster
Affects Versions: 3.0.0
Reporter: Tsuyoshi OZAWA
Assignee: Tsuyoshi OZAWA
To manage node/rack-level combining, MRAppMaster needs to have a management
information about outputs of completed MapTasks to be aggregated.
AggregationWaitMap is used so that MRAppMaster decides whether or not MapTasks
start to combine local MapOutputFiles.
AggregationWaitMap is a abstraction class of ConcurrentHashMap<String,
ArrayList<TaskAttemptCompletionEvent>. These Events are candidate files to be
aggregated.
When MapTasks are completed, MRAppMaster buffer TaskAttemptCompletionEvent into
AggregationWaitMap to delay reducers' fethcing outputs from mappers until
node-level aggregation are finished. After node-level aggreagtion, MRAppMaster
write back mapAttemptCompletionEvents, to restart reducers' feching outputs
from mappers.
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