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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2388) Map tasks with no locality hints should not always be considered off-rack
Date Wed, 16 Mar 2011 06:21:29 GMT
Map tasks with no locality hints should not always be considered off-rack
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                 Key: MAPREDUCE-2388
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2388
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: jobtracker
            Reporter: Todd Lipcon


When a map task has no locality hints, it's currently always considered "off-rack". This has
a couple side effects which aren't great, most notably that most schedulers will only assign
one off-rack task per heartbeat. This limits the scheduling throughput of these jobs.

It's unclear that it's always correct to schedule them as "node-local" either, though most
examples I can think of are probably better treated this way.

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