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https://issues.apache.org/jira/browse/LUCENE-1575?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12693843#action_12693843
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Shai Erera commented on LUCENE-1575:
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bq. So to be consistent maybe we create ScoringTopFieldCollector and
NonScoringTopFieldCollector?
And have STFC extend NSTFC? I see no reason to create an abstract
TopFieldCollector.
bq. This means we don't need ScoreCacheScorer? (because
ScoringTopFieldCollector will always grab the score). Though how do we change
FieldComparator API so as to not pass score around? All comparators except
RelevanceComparator don't use it.
I was actually thinking of that class for RelevanceComparator. So perhaps I can
implement the logic inside RelevanceComparator? Although this sounds like a
nice utility class, now that we have a setScorer on Collector - others may find
it useful too.
Remember that score-tracking is done for maxScore and ScoreDoc purposes (inside
STFC). The score in the FieldComparator API is used only in
RelevanceComparator, whether it's STFC or NSTFC.
bq. I think those must continue to use NSTFC for the existing methods (to
remain back compatible)
Did you mean continue to use STFC? The current behavior is that scoring is
tracked, I think.
bq. add a new search method that takes a boolean trackScore?
I actually prefer not to expose any more methods. IndexSearcher already has
plenty of them. Instead, one can use the very generic, simple and useful method
search(Query, Collector) and pass in a NSTFC instance. Otherwise we'll end up
adding many search() methods to IndexSearcher, if we continue with that
approach going forward.
> Refactoring Lucene collectors (HitCollector and extensions)
> -----------------------------------------------------------
>
> Key: LUCENE-1575
> URL: https://issues.apache.org/jira/browse/LUCENE-1575
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Shai Erera
> Fix For: 2.9
>
>
> This issue is a result of a recent discussion we've had on the mailing list.
> You can read the thread
> [here|http://www.nabble.com/Is-TopDocCollector%27s-collect()-implementation-correct--td22557419.html].
> We have agreed to do the following refactoring:
> * Rename MultiReaderHitCollector to Collector, with the purpose that it will
> be the base class for all Collector implementations.
> * Deprecate HitCollector in favor of the new Collector.
> * Introduce new methods in IndexSearcher that accept Collector, and deprecate
> those that accept HitCollector.
> ** Create a final class HitCollectorWrapper, and use it in the deprecated
> methods in IndexSearcher, wrapping the given HitCollector.
> ** HitCollectorWrapper will be marked deprecated, so we can remove it in 3.0,
> when we remove HitCollector.
> ** It will remove any instanceof checks that currently exist in IndexSearcher
> code.
> * Create a new (abstract) TopDocsCollector, which will:
> ** Leave collect and setNextReader unimplemented.
> ** Introduce protected members PriorityQueue and totalHits.
> ** Introduce a single protected constructor which accepts a PriorityQueue.
> ** Implement topDocs() and getTotalHits() using the PQ and totalHits members.
> These can be used as-are by extending classes, as well as be overridden.
> ** Introduce a new topDocs(start, howMany) method which will be used a
> convenience method when implementing a search application which allows paging
> through search results. It will also attempt to improve the memory
> allocation, by allocating a ScoreDoc[] of the requested size only.
> * Change TopScoreDocCollector to extend TopDocsCollector, use the topDocs()
> and getTotalHits() implementations as they are from TopDocsCollector. The
> class will also be made final.
> * Change TopFieldCollector to extend TopDocsCollector, and make the class
> final. Also implement topDocs(start, howMany).
> * Change TopFieldDocCollector (deprecated) to extend TopDocsCollector,
> instead of TopScoreDocCollector. Implement topDocs(start, howMany)
> * Review other places where HitCollector is used, such as in Scorer,
> deprecate those places and use Collector instead.
> Additionally, the following proposal was made w.r.t. decoupling score from
> collect():
> * Change collect to accecpt only a doc Id (unbased).
> * Introduce a setScorer(Scorer) method.
> * If during collect the implementation needs the score, it can call
> scorer.score().
> If we do this, then we need to review all places in the code where
> collect(doc, score) is called, and assert whether Scorer can be passed. Also
> this raises few questions:
> * What if during collect() Scorer is null? (i.e., not set) - is it even
> possible?
> * I noticed that many (if not all) of the collect() implementations discard
> the document if its score is not greater than 0. Doesn't it mean that score
> is needed in collect() always?
> Open issues:
> * The name for Collector
> * TopDocsCollector was mentioned on the thread as TopResultsCollector, but
> that was when we thought to call Colletor ResultsColletor. Since we decided
> (so far) on Collector, I think TopDocsCollector makes sense, because of its
> TopDocs output.
> * Decoupling score from collect().
> I will post a patch a bit later, as this is expected to be a very large
> patch. I will split it into 2: (1) code patch (2) test cases (moving to use
> Collector instead of HitCollector, as well as testing the new topDocs(start,
> howMany) method.
> There might be even a 3rd patch which handles the setScorer thing in
> Collector (maybe even a different issue?)
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