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https://issues.apache.org/jira/browse/LUCENE-4396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14098534#comment-14098534
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Michael McCandless commented on LUCENE-4396:
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Thanks Da, this is simpler.
I'm worried about how BooleanWeight.bulkScorer first pulls BulkScorer
for the clauses, and then sometimes also pulls Scorer; pulling a
Scorer is not that cheap an operation in general. Maybe if we added
cost() to bulk scorer we could avoid that? Or maybe we could look at
the BulkScorer, and if it's a DefaultBulkScorer, just ask it for the
Scorer it wrapped?
The small perf hit in BooleanScorer might just be that hotspot is less
happy because we converted the static classes to non-static ones
... just speculation though.
> 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, And.tasks, AndOr.tasks, AndOr.tasks,
> LUCENE-4396-simple.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, 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,
> merge-simple.perf, merge-simple.png, merge.perf, merge.png, perf.png,
> stat.cpp, stat.cpp, tasks.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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