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From "Matei Zaharia (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-4666) Launch reduces only after a few maps have run in the Fair Scheduler
Date Sat, 15 Nov 2008 23:54:44 GMT
Launch reduces only after a few maps have run in the Fair Scheduler
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                 Key: HADOOP-4666
                 URL: https://issues.apache.org/jira/browse/HADOOP-4666
             Project: Hadoop Core
          Issue Type: New Feature
          Components: contrib/fair-share
            Reporter: Matei Zaharia


It makes no sense to schedule reduces for a job before its maps have started running. As an
initial fix, we will wait until a certain percent have run (likely 10%). In the future it
would be good to choose the time to wait based on amount of map output data as well - launching
reducers that will mostly be idle is not helpful. Average amount of map output bytes per mapper
is easy to compute using counters in JobInProgress.

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