(Parallel-)MultiSearcher: using Sort object changes the scores
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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
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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