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From "Renaud Delbru (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1410) PFOR implementation
Date Mon, 15 Feb 2010 16:23:28 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12833872#action_12833872
] 

Renaud Delbru commented on LUCENE-1410:
---------------------------------------

When performing some tests on PFOR, I have noticed that your algorithm was favoring very small
numFrameBits for a very large number of exceptions. For example, on block of size 512, I have
noticed that many of the blocks was with bestFrameBits = 1, and the number of exceptions reaching
> 450.

I found that this was due to the seeting of the allowedNumExceptions variable (in the last
part of the PFOR#frameBitsForCompression() method) which was set to the number of current
exceptions + the maximum allowed (which at the end is generally extremely large).Is it a bug,
or is it something I don't understand in the current PFOR algorithm ?

P.S.: btw, the previous benchmark results I have posted are wrong due to a bug which was due
to the hardcoded byte buffer size (1024) in PForIndexInput/Output. I'll post soon updated
results, with a comparison with GroupVarInt (from WSDM09 - Jeff Dean talk).

> PFOR implementation
> -------------------
>
>                 Key: LUCENE-1410
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1410
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Other
>            Reporter: Paul Elschot
>            Priority: Minor
>         Attachments: autogen.tgz, LUCENE-1410-codecs.tar.bz2, LUCENE-1410b.patch, LUCENE-1410c.patch,
LUCENE-1410d.patch, LUCENE-1410e.patch, TermQueryTests.tgz, TestPFor2.java, TestPFor2.java,
TestPFor2.java
>
>   Original Estimate: 21840h
>  Remaining Estimate: 21840h
>
> Implementation of Patched Frame of Reference.

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