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https://issues.apache.org/jira/browse/LUCENE-1644?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael McCandless updated LUCENE-1644:
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Attachment: LUCENE-1644.patch
Attached rough patch -- javadocs are missing/not
updated, need to add new tests, need to fix QueryParser.jj, etc., but
all tests pass.
Here's what I did:
- Changed the MTQ.RewriteMethod class from a simple Parameter to its
own abstract base class w/ a single method, rewrite, which
MultiTermQuery.rewrite delegates to.
- Switched over CONSTANT_SCORE_FILTER_REWRITE,
SCORING_BOOLEAN_QUERY_REWRITE and
CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE. These classes are private
(they have no configuration), and I created final static singleton
instances for them.
- Created ConstantScoreAutoRewrite (and the default
CONSTANT_SCORE_AUTO_REWRITE instance) that you can configure based
on term count & doc count, as to when it cuts over to
CONSTANT_SCORE_FILTER_REWRITE.
This approach also has the benefit of allowing customization entirely,
if needed, of the "rewrite strategy", if none of the 4 choices work
for you.
> Enable MultiTermQuery's constant score mode to also use BooleanQuery under
> the hood
> -----------------------------------------------------------------------------------
>
> Key: LUCENE-1644
> URL: https://issues.apache.org/jira/browse/LUCENE-1644
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Fix For: 2.9
>
> Attachments: LUCENE-1644.patch, LUCENE-1644.patch
>
>
> When MultiTermQuery is used (via one of its subclasses, eg
> WildcardQuery, PrefixQuery, FuzzyQuery, etc.), you can ask it to use
> "constant score mode", which pre-builds a filter and then wraps that
> filter as a ConstantScoreQuery.
> If you don't set that, it instead builds a [potentially massive]
> BooleanQuery with one SHOULD clause per term.
> There are some limitations of this approach:
> * The scores returned by the BooleanQuery are often quite
> meaningless to the app, so, one should be able to use a
> BooleanQuery yet get constant scores back. (Though I vaguely
> remember at least one example someone raised where the scores were
> useful...).
> * The resulting BooleanQuery can easily have too many clauses,
> throwing an extremely confusing exception to newish users.
> * It'd be better to have the freedom to pick "build filter up front"
> vs "build massive BooleanQuery", when constant scoring is enabled,
> because they have different performance tradeoffs.
> * In constant score mode, an OpenBitSet is always used, yet for
> sparse bit sets this does not give good performance.
> I think we could address these issues by giving BooleanQuery a
> constant score mode, then empower MultiTermQuery (when in constant
> score mode) to pick & choose whether to use BooleanQuery vs up-front
> filter, and finally empower MultiTermQuery to pick the best (sparse vs
> dense) bit set impl.
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