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From "Yonik Seeley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-639) [PATCH] Slight performance improvement for readVInt() of IndexInput
Date Wed, 02 Aug 2006 18:38:16 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-639?page=comments#action_12425333 ] 
            
Yonik Seeley commented on LUCENE-639:
-------------------------------------

The XOR algorithm is a clever idea, but based on some quick tests of my own, it seems slower
than my "combine on exit" for what I would guess would be an important case of a mix of 1
and 2 byte vints.

for random numbers less than 128, the algorithms tied (not surprising).
for random numbers less than 200 (a mix of 1 and 2 byte vints):
  13% slower on AMD Opteron, Java 1.5.0_07 -server -Xbatch
  15% slower on P4, Java 6 beta2 -server -Xbatch



> [PATCH] Slight performance improvement for readVInt() of IndexInput
> -------------------------------------------------------------------
>
>                 Key: LUCENE-639
>                 URL: http://issues.apache.org/jira/browse/LUCENE-639
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: 2.0.0
>            Reporter: Johan Stuyts
>            Priority: Minor
>         Attachments: Lucene2ReadVIntPerformance.patch, readVInt performance results.pdf,
ReadVIntPerformanceMain.java
>
>
> By unrolling the loop in readVInt() I was able to get a slight, about 1.8 %, performance
improvement for this method. The test program invoked the method over 17 million times on
each run.
> I ran the performance tests on:
> - Windows XP Pro SP2
> - Sun JDK 1.5.0_07
> - YourKit 5.5.4
> - Lucene trunk

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