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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2027) fair share scheduler causes unnecessary preemption under some conditions
Date Mon, 23 Aug 2010 21:25:17 GMT
fair share scheduler causes unnecessary preemption under some conditions
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                 Key: MAPREDUCE-2027
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2027
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: contrib/fair-share
            Reporter: Joydeep Sen Sarma


When the cluster hits speculative cap - JobInProgress does not speculate any more. however
FairShare Scheduler continues to believe that tasks need to be speculated.

Under such conditions, FS Scheduler will start preempting repeatedly (because from it's perspective
- certain jobs are not getting the slots they deserve (for speculative tasks)).

There may be other reasons for excessive preemption as well - this one stood out clearly.

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