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https://issues.apache.org/jira/browse/LUCENE-4396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14073669#comment-14073669
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Michael McCandless commented on LUCENE-4396:
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Do we really need a separate class to make the decision about which scorer to
use? Seems like the added logic for when to use BNS is fairly small so we
could just add it into BQ's scorer method instead?
For bulkScorer, should we ever return BooleanScorer even when there are
required clauses? Or was that just commented out for temporary benchmarking so
we'd wrap BNS? When there is a required clause, if BNS is never slower than
BS, then instead of falling back to super.bulkScorer we could do the wrapping
ourselves there? Just to make it clearer we are using BNS ... or maybe just
put a comment saying so (replacing that TODO).
For the rules on when to use which scorer, it seems like we should take the
.cost() of the sub-clauses into account somehow...
> BooleanScorer should sometimes be used for MUST clauses
> -------------------------------------------------------
>
> Key: LUCENE-4396
> URL: https://issues.apache.org/jira/browse/LUCENE-4396
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Michael McCandless
> Attachments: And.tasks, AndOr.tasks, AndOr.tasks, LUCENE-4396.patch,
> LUCENE-4396.patch, LUCENE-4396.patch, LUCENE-4396.patch, LUCENE-4396.patch,
> LUCENE-4396.patch, LUCENE-4396.patch, LUCENE-4396.patch, LUCENE-4396.patch,
> LUCENE-4396.patch, SIZE.perf, all.perf, luceneutil-score-equal.patch,
> luceneutil-score-equal.patch, stat.cpp, stat.cpp
>
>
> Today we only use BooleanScorer if the query consists of SHOULD and MUST_NOT.
> If there is one or more MUST clauses we always use BooleanScorer2.
> But I suspect that unless the MUST clauses have very low hit count compared
> to the other clauses, that BooleanScorer would perform better than
> BooleanScorer2. BooleanScorer still has some vestiges from when it used to
> handle MUST so it shouldn't be hard to bring back this capability ... I think
> the challenging part might be the heuristics on when to use which (likely we
> would have to use firstDocID as proxy for total hit count).
> Likely we should also have BooleanScorer sometimes use .advance() on the subs
> in this case, eg if suddenly the MUST clause skips 1000000 docs then you want
> to .advance() all the SHOULD clauses.
> I won't have near term time to work on this so feel free to take it if you
> are inspired!
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