[jira] Commented: (LUCENE-2410) Optimize PhraseQuery

["Michael McCandless (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-2410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12885359#action_12885359 ] 

Michael McCandless commented on LUCENE-2410:
--------------------------------------------

Alas.... I think I somehow screwed up my performance tests above.

I'm testing search perf (working on LUCENE-2504), and in comparing search perf from 2.9.x -> 3.x, I only saw a ~20% speedup on the phrase query "united states", for a 5M doc Wikipedia index.  And, re-running the test on trunk pre and post this commit, I still see only ~20% gain.... still not sure what I did wrong.

I'll update CHANGES.  Two steps forward, one step back... sigh.

> Optimize PhraseQuery
> --------------------
>
>                 Key: LUCENE-2410
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2410
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Michael McCandless
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2410.patch, LUCENE-2410.patch, LUCENE-2410.patch, LUCENE-2410.patch, LUCENE-2410_rewrite.patch
>
>
> Looking the scorers for PhraseQuery, I think there are some speedups
> we could do:
>   * The AND part of the scorer (which advances to the next doc that
>     has all the terms), in PhraseScorer.doNext, should do the same
>     optimizing as BooleanQuery's ConjunctionScorer, ie sort terms from
>     rarest to most frequent.  I don't think it should use a linked
>     list/firstToLast() that it does today.
>   * We do way too much work now when .score() is not called, because
>     we go and find all occurrences of the phrase in the doc, whereas
>     we should stop only after finding the first and then go and count
>     the rest if .score() is called.
>   * For the exact case, I think we can use two int arrays to find the
>     matches.  The first array holds the count of how many times a term
>     in the phrase "matched" a phrase starting at that position.  When
>     that count == the number of terms in the phrase, it's a match.
>     The 2nd is a "gen" array (holds docID when that count was last
>     touched), to avoid clearing.  Ie when incrementing the count, if
>     the docID != gen, we reset count to 0.  I think this'd be faster
>     than the PQ we now use.  Downside of this is if you have immense
>     docs (position gets very large) we'd need 2 immense arrays.
> It'd be great to do LUCENE-1252 along with this, ie factor
> PhraseScorer into two AND'd sub-scorers (LUCENE-1252 is open for
> this).  The first one should be ConjunctionScorer, and the 2nd one
> checks the positions (ie, either the exact or sloppy scorers).  This
> would mean if the PhraseQuery is AND'd w/ other clauses (or, a filter
> is applied) we would save CPU by not checking the positions for a doc
> unless all other AND'd clauses accepted the doc.

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