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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-1630) Mating Collector and Scorer on doc Id orderness
Date Wed, 06 May 2009 20:12:30 GMT
Mating Collector and Scorer on doc Id orderness
-----------------------------------------------

                 Key: LUCENE-1630
                 URL: https://issues.apache.org/jira/browse/LUCENE-1630
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Search
            Reporter: Shai Erera
             Fix For: 2.9


This is a spin off of LUCENE-1593. This issue proposes to expose appropriate API on Scorer
and Collector such that one can create an optimized Collector based on a given Scorer's doc-id
orderness and vice versa. Copied from LUCENE-1593, here is the list of changes:

# Deprecate Weight and create QueryWeight (abstract class) with a new scorer(reader, scoreDocsInOrder),
replacing the current scorer(reader) method. QueryWeight implements Weight, while score(reader)
calls score(reader, false /* out-of-order */) and scorer(reader, scoreDocsInOrder) is defined
abstract.
#* Also add QueryWeightWrapper to wrap a given Weight implementation. This one will also be
deprecated, as well as package-private.
#* Add to Query variants of createWeight and weight which return QueryWeight. For now, I prefer
to add a default impl which wraps the Weight variant instead of overriding in all Query extensions,
and in 3.0 when we remove the Weight variants - override in all extending classes.
# Add to Scorer isOutOfOrder with a default to false, and override in BS to true.
# Modify BooleanWeight to extend QueryWeight and implement the new scorer method to return
BS2 or BS based on the number of required scorers and setAllowOutOfOrder.
# Add to Collector an abstract _acceptsDocsOutOfOrder_ which returns true/false.
#* Use it in IndexSearcher.search methods, that accept a Collector, in order to create the
appropriate Scorer, using the new QueryWeight.
#* Provide a static create method to TFC and TSDC which accept this as an argument and creates
the proper instance.
#* Wherever we create a Collector (TSDC or TFC), always ask for out-of-order Scorer and check
on the resulting Scorer isOutOfOrder(), so that we can create the optimized Collector instance.
# Modify IndexSearcher to use all of the above logic.

The only class I'm worried about, and would like to verify with you, is Searchable. If we
want to deprecate all the search methods on IndexSearcher, Searcher and Searchable which accept
Weight and add new ones which accept QueryWeight, we must do the following:
* Deprecate Searchable in favor of Searcher.
* Add to Searcher the new QueryWeight variants. Here we have two choices: (1) break back-compat
and add them as abstract (like we've done with the new Collector method) or (2) add them with
a default impl to call the Weight versions, documenting these will become abstract in 3.0.
* Have Searcher extend UnicastRemoteObject and have RemoteSearchable extend Searcher. That's
the part I'm a little bit worried about - Searchable implements java.rmi.Remote, which means
there could be an implementation out there which implements Searchable and extends something
different than UnicastRemoteObject, like Activeable. I think there is very small chance this
has actually happened, but would like to confirm with you guys first.
* Add a deprecated, package-private, SearchableWrapper which extends Searcher and delegates
all calls to the Searchable member.
* Deprecate all uses of Searchable and add Searcher instead, defaulting the old ones to use
SearchableWrapper.
* Make all the necessary changes to IndexSearcher, MultiSearcher etc. regarding overriding
these new methods.

One other optimization that was discussed in LUCENE-1593 is to expose a topScorer() API (on
Weight) which returns a Scorer that its score(Collector) will be called, and additionally
add a start() method to DISI. That will allow Scorers to initialize either on start() or score(Collector).
This was proposed mainly because of BS and BS2 which check if they are initialized in every
call to next(), skipTo() and score(). Personally I prefer to see that in a separate issue,
following that one (as it might add methods to QueryWeight).

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