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https://issues.apache.org/jira/browse/LUCENE-8759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16819179#comment-16819179
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Jim Ferenczi commented on LUCENE-8759:
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Thanks that looks cleaner, I think I got confused because I was not removing 1
to the floatBits. I tested your solution on all positive floats and it works so
I'll commit soon unless you have objections.
> BlockMaxConjunctionScorer's simplified way of computing max scores hurts
> performance
> ------------------------------------------------------------------------------------
>
> Key: LUCENE-8759
> URL: https://issues.apache.org/jira/browse/LUCENE-8759
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Priority: Minor
> Attachments: LUCENE-8759.patch
>
>
> BlockMaxConjunctionScorer computes the minimum value that the score should
> have after each scorer in order to be able to interrupt scorer as soon as
> possible. For instance say scorers A, B and C produce maximum scores that are
> equal to 4, 2 and 1. If the minimum competitive score is X, then the score
> after scoring A, B and C must be at least X, the score after scoring A and B
> must be at least X-1 and the score after scoring A must be at least X-1-2.
> However this is made a bit more complex than that due to floating-point
> numbers and the fact that intermediate score values are doubles which only
> get casted to a float after all values have been summed up. In order to keep
> things simple, BlockMaxConjunctionScore has the following comment and code
> {code}
> // Also compute the minimum required scores for a hit to be
> competitive
> // A double that is less than 'score' might still be converted to
> 'score'
> // when casted to a float, so we go to the previous float to avoid
> this issue
> minScores[minScores.length - 1] = minScore > 0 ?
> Math.nextDown(minScore) : 0;
> {code}
> It simplifies the problem by calling Math.nextDown(minScore). However this is
> problematic because it defeats the fact that TopScoreDocCollector calls
> setMinCompetitiveScore on the float value that is immediately greater than
> the k-th greatest hit so far.
> nextDown(minScore) is not the value that we need. The value that we need is
> the smallest double that converts to minScore when casted to a float, which
> would be half-way between nextDown(minScore) and minScore. In some cases this
> would help get better performance out of conjunctions, especially if some
> clauses produce constant scores.
> MaxScoreSumPropagator#setMinCompetitiveScore has the same issue.
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