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https://issues.apache.org/jira/browse/LUCENE-954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571339#action_12571339
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Christian Kohlschütter commented on LUCENE-954:
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You are right, Yonik.
Hits currently tries to "hide" this by normalizing the scores to a maximum of
1, simply by dividing the "raw" scores by the maximum score returned.
This is why the scores from Hits are currently not comparable to each other.
The suggested patch resolves this problem.
> Toggle score normalization in Hits
> ----------------------------------
>
> Key: LUCENE-954
> URL: https://issues.apache.org/jira/browse/LUCENE-954
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.2
> Environment: any
> Reporter: Christian Kohlschütter
> Attachments: hits-scoreNorm.patch
>
>
> The current implementation of the "Hits" class sometimes performs score
> normalization.
> In particular, whenever the top-ranked score is bigger than 1.0, it is
> normalized to a maximum of 1.0.
> In this case, Hits may return different score results than TopDocs-based
> methods.
> In my scenario (a federated search system), Hits delievered just plain wrong
> results.
> I was merging results from several sources, all having homogeneous statistics
> (similar to MultiSearcher, but over the Internet using HTTP/XML-based
> protocols).
> Sometimes, some of the sources had a top-score greater than 1, so I ended up
> with garbled results.
> I suggest to add a switch to enable/disable this score-normalization at
> runtime.
> My patch (attached) has an additional peformance benefit, since score
> normalization now occurs only when Hits#score() is called, not when creating
> the Hits result list. Whenever scores are not required, you save one
> multiplication per retrieved hit (i.e., at least 100 multiplications with the
> current implementation of Hits).
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