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From "Binglin Chang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-2910) Allow empty MapOutputFile segments
Date Tue, 30 Aug 2011 03:48:38 GMT
Allow empty MapOutputFile segments
----------------------------------

                 Key: MAPREDUCE-2910
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2910
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: task, tasktracker
    Affects Versions: 0.20.2, 0.23.0
            Reporter: Binglin Chang
            Priority: Minor
             Fix For: 0.23.0


As the scale of cluster and job get larger, we see a lot of empty partitions in MapOutputFile
due to large reduce numbers or partition skew. When map output compression is enabled, empty
map output partitions gets larger & has additional compressor/decompressor initialization
overhead. 
This can be optimized by allowing empty MapOutputFile segments, where the rawLength &
partLength of IndexRecord all equal to 0. Corresponding support need to be added to IFile
reader, writer, and reduce shuffle copier.


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