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From "Joydeep Sen Sarma (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2133) lag time for reduce speculation should start from completion of first mapper
Date Wed, 13 Oct 2010 20:15:37 GMT
lag time for reduce speculation should start from completion of first mapper
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                 Key: MAPREDUCE-2133
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2133
             Project: Hadoop Map/Reduce
          Issue Type: Bug
            Reporter: Joydeep Sen Sarma
            Priority: Minor


reducers don't make any progress until first mapper finishes. if the first mapper finishes
after the reduce speculation lag time - a bunch of (waiting) reducers may make some (non-zero)
progress while others stay at 0 progress. this causes a few reducers to be speculated (unnecessarily)
at this stage in the job. 

it seems that we should not start counting towards reduce stage lag time until at least one
mapper is done.

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