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https://issues.apache.org/jira/browse/LUCENE-8197?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16394670#comment-16394670
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Adrien Grand commented on LUCENE-8197:
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Actually it doesn't compute avgTf on the field that stores features but on the
field that is searched with full-text queries. For instance if you have two
fields 'body' (TextField) and 'features' (FeatureField), it tries to use a
weight for the query on 'features' that is eg. the IDF that a term that exists
in 1% (the 'cutoverFreq' parameter) of documents in 'body' would have. My goal
was to try to pick up a value that would make sure that the score contribution
that comes from features would have an impact on ranking but without dictating
ranking all the time either.
> Make top-k queries fast when static scoring signals are incorporated into the
> score
> -----------------------------------------------------------------------------------
>
> Key: LUCENE-8197
> URL: https://issues.apache.org/jira/browse/LUCENE-8197
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Priority: Minor
> Fix For: master (8.0)
>
> Attachments: LUCENE-8197.patch, LUCENE-8197.patch, LUCENE-8197.patch
>
>
> Block-max WAND (LUCENE-8135) and some earlier issues made Lucene faster at
> computing the top-k matches of boolean queries.
> It is quite frequent that users want to improve ranking and end up scoring
> with a formula that could look like {{bm25_score + w * log(alpha +
> pagerank)}} (w and alpha being constants, and pagerank being a per-document
> field value). You could do this with doc values and {{FunctionScoreQuery}}
> but unfortunately this will remove the ability to optimize top-k queries
> since the scoring formula becomes opaque to Lucene.
> I'd like to add a new field that allows to store such scoring signals as term
> frequencies, and new queries that could produce {{log(alpha + pagerank)}} as
> a score. Then implementing the above formula can be done by boosting this
> query with a boost equal to {{w}} and adding this boosted query as a SHOULD
> clause of a {{BooleanQuery}}. This would give Lucene the ability to compute
> top-k hits faster, especially but not only if the index is sorted by
> decreasing pagerank.
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