[jira] Commented: (LUCENE-954) Toggle score normalization in Hits

["Michael Busch (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598092#action_12598092 ] 

Michael Busch commented on LUCENE-954:
--------------------------------------

{quote}
If someone opens a Jira issue to deprecate the Hits class, and attaches a patch that does so and replaces examples of it's usage in the demo and tutorial, i'll certainly vote for it.
{quote}

Done with LUCENE-1290.
I'm waiting for your vote, Hoss ;-)

> 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, 2.3, 2.3.1, 2.4
>         Environment: any
>            Reporter: Christian Kohlschütter
>            Assignee: Otis Gospodnetic
>             Fix For: 2.4
>
>         Attachments: hits-scoreNorm.patch, LUCENE-954.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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