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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-469) (Parallel-)MultiSearcher: using Sort object changes the scores
Date Mon, 21 Nov 2005 19:52:41 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-469?page=comments#action_12358189 ] 

Doug Cutting commented on LUCENE-469:
-------------------------------------

TopDocs.maxScore should be private with public accessors.

I also agree that score normalization should only appear in scores from Hits.java.  (FYI,
the score normalization "feature" was added in the early days of Lucene when lots of folks
seemed to find scores greater than 1.0 disturbing.)


> (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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