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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 16:41:15 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-639?page=comments#action_12425563 ] 
            
Yonik Seeley commented on LUCENE-639:
-------------------------------------

> Yonik, please let me know where you think the test that I provided is flawed. 

Tests are always flawed :-)   If our tests don't exactly agree, It doesn't mean one is incorrect.
 I already had a little test framework from before so I used that... it doesn't mean there
is anything wrong with your tests, but more validation is better.

If there is one thing in your tests that I think could perhaps be improved, it's the distribution
of VInts.
Testing 1 byte vints separately from 2 byte vints, etc, will yield different results than
testing a realistic mix because of processor branch prediction.

I really want to test with a real Lucene index (I've already started coming up with a simple
test).  That will be a better real-world  test IMO, and trump both of our current test frameworks.


> [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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