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[jira] Updated: (LUCENE-469) (Parallel-)MultiSearcher: using Sort object

Subject: [jira] Updated: (LUCENE-469) (Parallel-)MultiSearcher: using Sort object changes the scores
From: "Luc Vanlerberghe (JIRA)"
Date: Mon, 21 Nov 2005 19:36:41 +0100 CET
     [ http://issues.apache.org/jira/browse/LUCENE-469?page=all ]

Luc Vanlerberghe updated LUCENE-469:

    Attachment: MultiSearcherSort.patch

My thoughts exactly!

For the expert routines, there's no mention in the javadoc about the scoring 
being applied, so nobody should depend on it.  If they did, well, they're 
experts, right? :)

This is my complete patch to correct the problem and I do indeed propose to add 
a field maxScore to TopDocs that is used in Hits to normalize the results at as 
the very last step.

All the TestCases pass after applying this patch.

> (Parallel-)MultiSearcher: using Sort object changes the scores
> --------------------------------------------------------------
>          Key: LUCENE-469
>          URL: http://issues.apache.org/jira/browse/LUCENE-469
>      Project: Lucene - Java
>         Type: Bug
>   Components: Search
>     Versions: CVS Nightly - Specify date in submission
>  Environment: 21 november 2005, revision 345901
>     Reporter: Luc Vanlerberghe
>  Attachments: MultiSearcherSort.patch, TestMultiSearcher.patch
> Example: 
> Hits hits=multiSearcher.search(query);
> returns different scores for some documents than
> Hits hits=multiSearcher.search(query, Sort.RELEVANCE);
> (both for MultiSearcher and ParallelMultiSearcher)
> The documents returned will be the same and in the same order, but the scores 
> in the second case will seem out of order.
> Inspecting the Explanation objects shows that the scores themselves are ok, 
> but there's a bug in the normalization of the scores.
> The document with the highest score should have score 1.0, so all document 
> scores are divided by the highest score.  (Assuming the highest score was>1.0)
> However, for MultiSearcher and ParallelMultiSearcher, this normalization 
> factor is applied *per index*, before merging the results together (the merge 
> itself is ok though).
> An example: if you use
> Hits hits=multiSearcher.search(query, Sort.RELEVANCE);
> for a MultiSearcher with two subsearchers, the first document will have score 
> 1.0.
> The next documents from the same subsearcher will have decreasing scores.
> The first document from the other subsearcher will however have score 1.0 
> again !
> The same applies for other Sort objects, but it is less visible.
> I will post a TestCase demonstrating the problem and suggested patches to 
> solve it in a moment...

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