[HADOOP-1719] Improve the utilization of shuffle copier threads - ASF JIRA

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Details

Type: Improvement
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: None
Fix Version/s: 0.16.0
Component/s: None
Labels:
- pull-request-available

Description

In the current design, the scheduling of copies is done and the scheduler (the main loop in fetchOutputs) won't schedule anything until it hears back from at least one of the copier threads. Due to this, the main loop won't query the TaskTracker asking for new map locations and may not be using all the copiers effectively. This may not be an issue for small-sized map outputs, where at steady state, the frequency of such notifications is frequent.
Ideally, we should schedule all what we can, and, depending on how busy we currently are, query the tasktracker for more map locations.