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From Shai Erera <ser...@gmail.com>
Subject Re: Proposal: Scorer api change
Date Wed, 09 Jun 2010 05:37:51 GMT
I agree w/ both Doron and Earwin, on different points though.

I don't think the method call is an overhead John. You don't need to
reiterate it. The compiler does make optimizations and inlines such
code/calls if it can. More than that, the query processing involves so much
method calls, that I do think that's insignificant.

And my last sentence is related to Earwin's thoughts -- it's insignificant
compared to writing complicated code which needs to support arbitrary doc
scoring - code that will 99.99999999% of the times won't be called at all,
yet we'll need to go through hoola hoops to support it in all Lucene Scorers
and custom ones (outside Lucene). So whatever overhead you claim the
delegate call adds to the search, I think it's insignificant if in order to
avoid it we need to break the API and introduce more complicated code.

One complication is preparing for a case where someone asks to score a doc
id N, when all Scorers are at doc id N+1 (or further). How do you do that?
restart? What if the Scorers don't agree on doc id N at all? What will be
the score then?

When you ask Scorer.score(), you know it does so on the current doc id,
which all sub scorers agreed on. It is a 'match'. I like Earwin's analogy to
matcher (though I'm not familiar with MG4J) -- it's like the Java Matcher.
You ask a Pattern to match something, and receive a Matcher, on which you
can do what you want. You don't ask the Pattern to get you the next match,
and then ask it again to do something with it ... not sure if my analogy is
1:1 with the proposed change, but I feel that the proposed change decouples
matching and scoring unnecessarily.

Shai

On Wed, Jun 9, 2010 at 1:50 AM, Earwin Burrfoot <earwin@gmail.com> wrote:

> Some people don't do IO while searching at all. When you're over
> certain qps/index size threshold, you need less nodes to keep all your
> index (or its hot parts) in memory, than to keep combined IO subsystem
> throughput high enough to satisfy disc-based search demands.
>
> 2010/6/9 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
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >> >
> >>> >> >>
> >>> >> >>
> >>> >> >>
> ---------------------------------------------------------------------
> >>> >> >> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
> >>> >> >> For additional commands, e-mail: dev-help@lucene.apache.org
> >>> >> >>
> >>> >> >
> >>> >> >
> >>> >>
> >>> >>
> >>> >>
> >>> >> --
> >>> >> Kirill Zakharenko/Кирилл Захаренко (earwin@gmail.com)
> >>> >> Phone: +7 (495) 683-567-4
> >>> >> ICQ: 104465785
> >>> >>
> >>> >>
> ---------------------------------------------------------------------
> >>> >> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
> >>> >> For additional commands, e-mail: dev-help@lucene.apache.org
> >>> >>
> >>> >
> >>> >
> >>>
> >>>
> >>>
> >>> --
> >>> Kirill Zakharenko/Кирилл Захаренко (earwin@gmail.com)
> >>> Phone: +7 (495) 683-567-4
> >>> ICQ: 104465785
> >>>
> >>> ---------------------------------------------------------------------
> >>> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
> >>> For additional commands, e-mail: dev-help@lucene.apache.org
> >>>
> >>
> >
> >
>
>
>
> --
> Kirill Zakharenko/Кирилл Захаренко (earwin@gmail.com)
> Phone: +7 (495) 683-567-4
> ICQ: 104465785
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
> For additional commands, e-mail: dev-help@lucene.apache.org
>
>

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