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Review request for hive and Ning Zhang.


Summary
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By tweaking the RCFile$Reader implementation to allow more efficient memory 
access I was able to reduce CPU usage. I measured the speed required to scan a 
gzipped RCFile, decompress and assemble into records. CPU time was reduced by 
about 7% for a full table scan, An improvement of about 2% was realised when a 
smaller subset of columns (3-5 out of tens) were selected.


This addresses bug HIVE-2350.
    https://issues.apache.org/jira/browse/HIVE-2350


Diffs
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  trunk/ql/src/java/org/apache/hadoop/hive/ql/io/RCFile.java 1154070 

Diff: https://reviews.apache.org/r/1309/diff


Testing
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Ran TestRCFile unit test.  Manually tested reading from warehouse table.


Thanks,

Tim

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