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https://issues.apache.org/jira/browse/LUCENE-6276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14909685#comment-14909685
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Paul Elschot commented on LUCENE-6276:
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As to TwoPhaseIterator or DocIdSetIterator, I think this boils down to whether
the leading iterator in ConjunctionDISI should be chosen using the expected
number of matching docs only, or also using the totalTermFreq's somehow. This
is for more complex queries, for example a conjunction with at least one phrase
or SpanNearQuery.
But for the more complex queries two phase approximation is already in place,
so having matchCost() only in the two phase code could be enough even for these
queries.
> Add matchCost() api to TwoPhaseDocIdSetIterator
> -----------------------------------------------
>
> Key: LUCENE-6276
> URL: https://issues.apache.org/jira/browse/LUCENE-6276
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Robert Muir
>
> We could add a method like TwoPhaseDISI.matchCost() defined as something like
> estimate of nanoseconds or similar.
> ConjunctionScorer could use this method to sort its 'twoPhaseIterators' array
> so that cheaper ones are called first. Today it has no idea if one scorer is
> a simple phrase scorer on a short field vs another that might do some geo
> calculation or more expensive stuff.
> PhraseScorers could implement this based on index statistics (e.g.
> totalTermFreq/maxDoc)
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