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Posted to dev@lucene.apache.org by "Christian Kohlschütter (JIRA)" <ji...@apache.org> on 2007/07/09 18:55:04 UTC
[jira] Updated: (LUCENE-954) Toggle score normalization in Hits
[ https://issues.apache.org/jira/browse/LUCENE-954?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Christian Kohlschütter updated LUCENE-954:
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Attachment: hits-scoreNorm.patch
Adds a switch to enable/disable Hits-based score normalization.
> 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
> Fix For: 2.2
>
> 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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