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From "Srikanth Kakani (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-2131) Speculative execution should be allowed for reducers only
Date Tue, 30 Oct 2007 23:54:50 GMT
Speculative execution should be allowed for reducers only
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                 Key: HADOOP-2131
                 URL: https://issues.apache.org/jira/browse/HADOOP-2131
             Project: Hadoop
          Issue Type: Improvement
          Components: mapred
         Environment: Hadoop job, map fetches data from external systems
            Reporter: Srikanth Kakani
            Priority: Critical
             Fix For: 0.15.0


Consider hadoop jobs where maps fetch data from external systems, and emit the data. The reducers
in this are identity reducers. The data processed by these jobs is huge. There could be slow
nodes in this cluster and some of the reducers run twice as slow as their counterparts. This
could result in a long tail. Speculative execution would help greatly in such cases. However
given the current hadoop, we have to select speculative execution for both maps and reducers.
In this case hurting the map performance as they are fetching data from external systems thereby
overloading the external systems.

Speculative execution only on reducers would be a great way to solve this problem.

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