Support getMaxScore of ConjunctionScorer for non top level scoring clause

[mrkm4ntr]

Description

After introducing topLevelScoringClause, ConjunctionScorer with multiple scorers can be used for non top level scoring clause conjunctions instead of BlockMaxConjunctionScorer even requiredScorers is empty. In such case, ConjunctionScorer returns Infinity as maxScore and it ruins some optimizations like parent WANDScorer.
https://github.com/apache/lucene/blob/7d35ae485807147460f63ea58ae495124e972e13/lucene/core/src/java/org/apache/lucene/search/Boolean2ScorerSupplier.java#L218C77-L218C98

[jpountz]

Thanks for looking into this, can you explain what kind of queries perform better with this change?

[mrkm4ntr]

For this case. Suppose ScorerA, B, and C can return valid maxScore. If the ScorerD is dominant, larger minCompetitiveScore is set to WANDScorer. But ConjunctionScorer returns Infinity as maxScore and scaledMaxScore becomes 0. Then WANDScorer cannot skip docs well. Is my understanding correct?

DisjunctionMaxScorer(scorers=[
  WANDScorer(scorers=[ConjunctionScorer(ScorerA, ScorerB), ScorerC]),
  ScorerD
], tieBreakerMultiplier=0.0)

[jpountz]

OK, I see, it's about conjunctions within disjunctions. Thanks for explaining.

[jpountz]

The change looks good to me, can you add a CHANGES entry?

[mrkm4ntr]

Thanks. 9.10 as well?

[jpountz]

Yes please.

[mrkm4ntr]

Added, thanks.