TaskLauncher remains stuck on tasks waiting for free nodes even if task is
killed.
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Key: MAPREDUCE-1398
URL: https://issues.apache.org/jira/browse/MAPREDUCE-1398
Project: Hadoop Map/Reduce
Issue Type: Bug
Components: tasktracker
Reporter: Hemanth Yamijala
Tasks could be assigned to trackers for slots that are running other tasks in a
commit pending state. This is an optimization done to pipeline task assignment
and launch. When the task reaches the tracker, it waits until sufficient slots
become free for it. This wait is done in the TaskLauncher thread. Now, while
waiting, if the task is killed externally (maybe because the job finishes,
etc), the TaskLauncher is not notified of this. So, it continues to wait for
the killed task to get sufficient slots. If slots do not become free for a long
time, this would result in considerable delay in waking up the TaskLauncher
thread. If the waiting task happens to be a high RAM task, then it is also
wasteful, because by waking up, it can make way for normal tasks that can run
on the available number of slots.
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