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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2201) Quicker preemption causes excessive preemption in FairScheduler
Date Wed, 24 Nov 2010 23:49:14 GMT
Quicker preemption causes excessive preemption in FairScheduler

                 Key: MAPREDUCE-2201
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2201
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: contrib/fair-share
            Reporter: Joydeep Sen Sarma

One problem we are seeing is where FairScheduler repeatedly preempts for the same job. This
is presumably because our preemption interval is set to a low number (1 minute). FS queues
up N tasks to be killed - but in 1 min it is not able to kill  and schedule new tasks on all
these slots. As a result, after 1 min - it again preempts a whole bunch of tasks.

We could (and probably will) workaround this by increasing the preemption interval. However
- this gives us a hard tradeoff between accurate preemption and timely preemption. Not good.
Ideally we want to make the first set of preemptions quickly (to provide responsive behavior
to new jobs for example) - but wait (to make sure that the kill actions have actually been
processed) thereafter.

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