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https://issues.apache.org/jira/browse/LUCENE-1575?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael McCandless updated LUCENE-1575:
---------------------------------------
Attachment: LUCENE-1575.patch
OK, I attached a new patch with some minor changes:
* Beefed up javadocs in Collector.java; fixed other javadocs
warnings. Tweaked CHANGES.txt.
* Renamed PositiveOnlyScoresCollector -->
PositiveScoresOnlyCollector
And also came across these questions/issues:
* TopFieldCollector's updateBottom & add methods take score, and are
passed score from the non-scoring collectors, but shouldn't?
* TermScorer need not override score(HitCollector hc) (super does
the same thing).
* The changes to TermScorer make me a bit nervous. EG, the new
InternalScorer: will it hurt performance? Also this part:
{code}
+ // Set the Scorer doc and score before calling collect in case it will
be
+ // used in collect()
+ s.d = doc;
+ s.score = score;
+ c.collect(doc); // collect score
{code}
is spooky: I don't like how we worry that one may call scorer.doc() (I
don't like the ambiguity in the API -- we both pass doc and fear you
may call scorer.doc()). Not sure how to resolve it.
* Hmm -- we added a new abstract method to
src/java/org/apache/lucene/search/Searcher.java (that accepts
Collector). Should that method be concrete (and throw UOE), for
back compat?
* We've also added a method to the "Searchable" interface, which is
a break in back-compat. But my feeling is we should allow this
break (but Shai can you add another Note at the top of
CHANGES.txt, calling this out?).
> 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
> Assignee: Michael McCandless
> Fix For: 2.9
>
> Attachments: LUCENE-1575.1.patch, LUCENE-1575.2.patch,
> LUCENE-1575.3.patch, LUCENE-1575.4.patch, LUCENE-1575.5.patch,
> LUCENE-1575.6.patch, LUCENE-1575.patch, LUCENE-1575.patch
>
>
> 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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