Re: What's the purpose of hashing docid in BooleanScorer; DisjunctionScorer

[Paul Elschot <pa...@xs4all.nl>]

On Monday 18 October 2004 23:04, Doug Cutting wrote:
> Christoph Goller wrote:
> > With the current scorer API one could get rid of buckettable and
> > advance all subscores only by one document each time. I am not sure
> > whether the bucketable implementation is really much more efficient.
> > I only see the advantage of inlining some of the scorer.next and
> > score.score code.
>
> Indeed, sub-scorers could be, e.g., kept in a priority queue.  This is
> done in ConjunctionScorer, PhraseScorer, etc.  However this adds a
> priority queue update to the inner search loop.  With long queries and
> with common terms this overhead can be significant.  With short queries
> and/or with rare terms the current ScoreTable-based implementation may
> indeed be slower, but I believe with longer queries containing common
> terms it is substantially faster.
>
> This algorithm is described in:
>
> http://lucene.sourceforge.net/papers/riao97.ps
>
> If we had a priority-queue-based implementation then we could benchmark
> these.  If we found that one were faster than the other for particular
> classes of queries then we could have a query optimizer which
> automatically selects the most efficient implementation...

I have a DisjunctionScorer based on a PriorityQueue lying around,
but I can't benchmark it myself at the moment. In case there is
interest, I'll gladly adapt it to org.apache.lucene.search and 
add it in bugzilla.

Regards,
Paul Elschot


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Re: What's the purpose of hashing docid in BooleanScorer; DisjunctionScorer

[Doug Cutting <cu...@apache.org>]

Paul Elschot wrote:
> I have a DisjunctionScorer based on a PriorityQueue lying around,
> but I can't benchmark it myself at the moment. In case there is
> interest, I'll gladly adapt it to org.apache.lucene.search and 
> add it in bugzilla.

This should look a lot like SpanOrQuery.getSpans().

On a related note, I implemented ConjunctionScorer using Java's 
collection classes rather than a Lucene priority queue, just to see if I 
could.  It turns out to have to allocate memory in sortScorers() which 
makes it slower than it could be, but I have not yet gotten around to 
fixing it.  I'd like to re-write this to look like PhraseScorer and 
NearSpans, which operate without allocation.

Doug




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