Hi Doron:

Re: " comparing to all other IO ops and computations done by the stack of scorers"

Lucene caches rather well and compresses well enough that the IO cache is effective enough that you are not really paying for disk movement most of the time. As for the stack of scores, that is actually my point, the number of times score is called is much less than that of nextDoc/advance (sorry have to keep on re-iterating this).

The overhead of delegation for large result sets is not insignificant because it is called in a inner/tight loop. (again, sorry to have to re-iterate this)

Subclassing works fine, but in the case you don't know which query type to subclass, it is not viable.

-John
   

2010/6/8 Doron Cohen <cdoronc@gmail.com>
I too tend to ignore the overhead of delegated calls, especially comparing to all other IO ops and computations done by the stack of scorers, but accepting that you cannot ignore it, could you achieve the same goal by sub-classing the top query where you subclass its weight to return a sub-class of its scorer which would only override score() but not the other methods, and in score would apply that eg decay logic? This way no delegation is required for the other methods. A disadvantage of this is that you would need subclass like this any kind of top level query that might come up in your app - so not sure if this is really acceptable in your case. Another disadvantage is that this is a much more complicated code to write.

Doron


2010/6/8 John Wang <john.wang@gmail.com>
Wouldn't you get it as well with proposed api?
You would still be able to iterate the doc and at that point call score with the docid. If you call score() along with iteration, you would still get the information no?
Making scorer take a docid allows you score any docid in the reader if the query wants it to. Wouldn't it make it more flexible?

-John


On Tue, Jun 8, 2010 at 10:54 AM, Earwin Burrfoot <earwin@gmail.com> wrote:
To compute a score you have to see which of your subqueries did not
match, which did, and what are the docfreqs/positions for them.
When iterating, and calling score() only for current doc - parts of
this data (maybe even all of it, not sure) is already gathered for
you. If you allow calling score(int doc) - for arbitrary docId, you'll
have to redo this work.

2010/6/8 John Wang <john.wang@gmail.com>:
> Hi Earwin:
>
>      I am not sure I understand here, e.g. what si the difference between:
>
>      float myscorinCode(){
>          computeMyScore(scorer.score());
>      }
>
>      and
>
>       float myscorinCode(){
>          computeMyScore(scorer.score(scorer.getDocIdSetIterator().docID());
>       }
>
>       In the case of BQ, when you get a hit, would you still be able to call
> subscorer.score(hit)? Why is the point of iteration important for BQ?
>
>       please elaborate.
>
> Thanks
>
> -John
>
> On Tue, Jun 8, 2010 at 10:10 AM, Earwin Burrfoot <earwin@gmail.com> wrote:
>>
>> The problem with your proposal is that, currently, Lucene uses current
>> iteration state to compute score.
>> I.e. it already knows which of SHOULD BQ clauses matched for current
>> doc, so it's easier to calculate the score.
>> If you change API to allow scoring arbitrary documents (even those
>> that didn't match the query at all), you're opening a can of worms :)
>>
>> As an alternative, you can try looking at MG4J sources. As far as I
>> understand, their scoring is decoupled from matching, just like you
>> (and I bet many more people) want. The matcher is separate, and the
>> scoring entity accepts current matcher state instead of document id,
>> so you get the best of both worlds.
>>
>> On Tue, Jun 8, 2010 at 21:01, John Wang <john.wang@gmail.com> wrote:
>> > re: But Scorer is itself an iterator, so what prevents you from calling
>> > nextDoc and advance on it without score()
>> >
>> > Nothing. It is just inefficient to pay the method call overhead just to
>> > overload score.
>> >
>> > re: If I were in your shoes, I'd simply provider a Query wrapper. If CSQ
>> > is not good enough I'd just develop my own.
>> >
>> > That is what I am doing. I am just proposing the change (see my first
>> > email)
>> > as an improvement.
>> >
>> > re: Scorer is itself an iterator
>> >
>> > yes, that is the current definition. The point of the proposal is to
>> > make
>> > this change.
>> >
>> > -John
>> >
>> > On Tue, Jun 8, 2010 at 9:45 AM, Shai Erera <serera@gmail.com> wrote:
>> >>
>> >> Well … I don't know the reason as well and always thought Scorer and
>> >> Similarity are confusing.
>> >>
>> >> But Scorer is itself an iterator, so what prevents you from calling
>> >> nextDoc and advance on it without score(). And what would the returned
>> >> DISI do when nextDoc is called, if not delegate to its subs?
>> >>
>> >> If I were in your shoes, I'd simply provider a Query wrapper. If CSQ
>> >> is not good enough I'd just develop my own.
>> >>
>> >> But perhaps others think differently?
>> >>
>> >> Shai
>> >>
>> >> On Tuesday, June 8, 2010, John Wang <john.wang@gmail.com> wrote:
>> >> > Hi Shai:
>> >> >     I am not sure I understand how changing Similarity would solve
>> >> > this
>> >> > problem, wouldn't you need the reader?
>> >> >     As for PayloadTermQuery, payload is not always the most efficient
>> >> > way of storing such data, especially when number of terms << numdocs.
>> >> > (I am
>> >> > not sure accessing the payload when you iterate is a good idea, but
>> >> > that is
>> >> > another discussion)
>> >> >
>> >> >     Yes, what I described is exactly a simple CustomScoreQuery for a
>> >> > special use-case. The problem is also in CustomScoreQuery, where
>> >> > nextDoc and
>> >> > advance are calling the sub-scorers as a wrapper. This can be avoided
>> >> > if the
>> >> > Scorer returns an iterator instead.
>> >> >
>> >> >     Separating scoring and doc iteration is a good idea anyway. I
>> >> > don't
>> >> > know the reason to combine them originally.
>> >> > Thanks
>> >> > -John
>> >> >
>> >> >
>> >> > On Tue, Jun 8, 2010 at 8:47 AM, Shai Erera <serera@gmail.com> wrote:
>> >> >
>> >> > So wouldn't it make sense to add some method to Similarity? Which
>> >> > receives the doc Id in question maybe ... just thinking here.
>> >> >
>> >> > Factoring Scorer like you propose would create 3 objects for
>> >> > scoring/iterating: Scorer (which really becomes an iterator),
>> >> > Similarity and
>> >> > CustomScoreFunction ...
>> >> >
>> >> > Maybe you can use CustomScoreQuery? or PayloadTermQuery? depends how
>> >> > you
>> >> > compute your age decay function (where you pull the data about the
>> >> > age of
>> >> > the document).
>> >> >
>> >> > Shai
>> >> >
>> >> >
>> >> > On Tue, Jun 8, 2010 at 6:41 PM, John Wang <john.wang@gmail.com>
>> >> > wrote:
>> >> > Hi Shai:
>> >> >     Similarity in many cases is not sufficient for scoring. For
>> >> > example,
>> >> > to implement age decaying of a document (very useful for corpuses
>> >> > like news
>> >> > or tweets), you want to project the raw tfidf score onto a time
>> >> > curve, say
>> >> > f(x), to do this, you'd have a custom scorer that decorates the
>> >> > underlying
>> >> > scorer from your say, boolean query:
>> >> >
>> >> >
>> >> >
>> >> > public float score(){    return myFunc(innerScorer.score());}
>> >> >     This is fine, but then you would have to do this as well:
>> >> > public int nextDoc(){
>> >> >
>> >> >
>> >> >    return innerScorer.nextDoc();}
>> >> > and also:
>> >> > public int advance(int target){   return innerScorer.advance();}
>> >> > The difference here is that nextDoc and advance are called far more
>> >> > times as
>> >> > score. And you are introducing an extra method call for them, which
>> >> > is not
>> >> > insignificant for queries result in large recall sets.
>> >> >
>> >> >
>> >> >
>> >> > Hope this makes sense.
>> >> > Thanks
>> >> > -John
>> >> > On Tue, Jun 8, 2010 at 5:02 AM, Shai Erera <serera@gmail.com> wrote:
>> >> > I'm not sure I understand what you mean - Scorer is a DISI itself,
>> >> > and
>> >> > the scoring formula is mostly controlled by Similarity.
>> >> >
>> >> > What will be the benefits of the proposed change?
>> >> >
>> >> > Shai
>> >> >
>> >> > On Tue, Jun 8, 2010 at 8:25 AM, John Wang <john.wang@gmail.com>
>> >> > wrote:
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > Hi guys:
>> >> >
>> >> >     I'd like to make a proposal to change the Scorer class/api to the
>> >> > following:
>> >> >
>> >> >
>> >> > public abstract class Scorer{
>> >> >    DocIdSetIterator getDocIDSetIterator();
>> >> >    float score(int docid);
>> >> > }
>> >> >
>> >> > Reasons:
>> >> >
>> >> > 1) To build a Scorer from an existing Scorer (e.g. that produces raw
>> >> > scores from tfidf), one would decorate it, and it would introduce
>> >> > overhead
>> >> > (in function calls) around nextDoc and advance, even if you just want
>> >> > to
>> >> > augment the score method which is called much fewer times.
>> >> >
>> >> > 2) The current contract forces scoring on the currentDoc in the
>> >> > underlying iterator. So once you pass "current", you can no longer
>> >> > score. In
>> >> > one of our use-cases, it is very inconvenient.
>> >> >
>> >> > What do you think? I can go ahead and open an issue and work on a
>> >> > patch
>> >> > if I get some agreement.
>> >> >
>> >> > Thanks
>> >> >
>> >> > -John
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >>
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>> >>
>> >
>> >
>>
>>
>>
>> --
>> Kirill Zakharenko/Кирилл Захаренко (earwin@gmail.com)
>> Phone: +7 (495) 683-567-4
>> ICQ: 104465785
>>
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>
>



--
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