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From "Shai Erera (JIRA)" <>
Subject [jira] Commented: (LUCENE-1630) Mating Collector and Scorer on doc Id orderness
Date Mon, 15 Jun 2009 12:15:07 GMT


Shai Erera commented on LUCENE-1630:

Ok I was just about to post the patch, when the Spatial tests failed. After some investigation,
I found out the following, and would appreciate your suggestions.
weight, Filter filter, final int nDocs, Sort sort, boolean fillFields) I wrote the following

    // try to create a Scorer in out-of-order mode, just to know which TFC
    // version to instantiate.
    boolean docsScoredInOrder = false;
    if (subReaders.length > 0) {
      docsScoredInOrder = !weight.scorer(subReaders[0], false, false).scoresOutOfOrder();
    TopFieldCollector collector = TopFieldCollector.create(sort, nDocs,
        fillFields, fieldSortDoTrackScores, fieldSortDoMaxScore, docsScoredInOrder);
    search(weight, filter, collector);

For clarification - I need to know which TFC instance to create (in-order / out-of-order).
For that, I need to first create a Scorer, asking for out-of-order one, and then check whether
the Scorer is indeed an out-of-order or not. That's a dummy Scorer, as I never use it afterwards,
but since we didn't want to add scoresOutOfOrder to Weight, but Scorer, I don't have any other

For Spatial, this creates a problem. One of the tests uses ConstantScoreQuery and passes in
a Filter. CSQ.scorer() creates a new Scorer and uses the given Filter as reference. In Spatial,
every time Filter.getDocIdSet() is called, the internal filter populates a WeakHashMap of
distances (with the doc id as key), and doesn't clear it between invocations. It also updates
the "base" of the key to handle multiple readers. Therefore the docs of the first reader are
added twice - once for the dummy invocation and the second time since the "base" is updated
(, line 222) to reader.maxDoc().

I tried to create a new "distances" map on every invocation, but then another test fails.
I don't know this code very well, and I don't know which is the best solution:

* Complicate the code in IndexSearcher to create a Scorer, then collect it and then proceed
w/ iterating on the readers, from the 2nd forward. This is a real ugly change, I tried it
and quickly reverted. It also breaks the current beauty of having all the search methods call
search(Weight, Filter, Collector).

* Fix LatLongDistanceFilter code to check if reader.maxDoc() == nextOffset, then do nextOffset
-= reader.maxDoc(). This is not pretty either, since it assumes a certain implementation and
use of it, which I don't like either.

* Add scoresOutOfOrder to Weight, but I don't know if we want to add this "knowledge" to Weight,
and it fits nicely in Scorer.

Any suggestions? perhaps a different fix to Spatial?

> Mating Collector and Scorer on doc Id orderness
> -----------------------------------------------
>                 Key: LUCENE-1630
>                 URL:
>             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
> # 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 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
> # 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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