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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 Thu, 03 Aug 2006 19:36:15 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-639?page=comments#action_12425597 ] 
            
Yonik Seeley commented on LUCENE-639:
-------------------------------------

Here's the simple TermDoc iteration test I used:
http://svn.apache.org/viewvc/lucene/java/trunk/src/test/org/apache/lucene/index/TestTermdocPerf.java

I think our attempts at optimization might be foiled by the larger method size, and the fact
that so many vints are going to be a single byte (the term freqs are interleaved with the
doc increments).  Hotspot might have an easier time with the small method, and the branch
predictor will have fewer branches to track, etc. who knows...

If anyone else feels like running on a different processor or with different params, please
have at it.  For me, the "more real lucene" test on the P4 was enough to dissuade me from
pursuing this further (yet again).

> [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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