[jira] [Commented] (LUCENE-6276) Add matchCost() api to TwoPhaseDocIdSetIterator

["Paul Elschot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-6276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14909660#comment-14909660 ] 

Paul Elschot commented on LUCENE-6276:
--------------------------------------

>From the javadocs of DocIdSetIterator.cost():
This is generally an upper bound of the number of documents this iterator might match, but may be a rough heuristic, hardcoded value, or otherwise completely inaccurate.

Perhaps this cost method can be renamed to for example expectedMaxMatchingDocs() with these javadocs:
This an expected upper bound of the number of documents this iterator might match.

Would it make sense to put matchCost() at DocIdSetIterator?

> 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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