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Re: I just don't get wildcards at all.

Subject: Re: I just don't get wildcards at all.
From: Chris Hostetter
Date: Mon, 10 Apr 2006 11:08:29 -0700 PDT
: Let's claim that all my clauses contain wildcards. What I *think* that means
: is that I can't very well use a filter "the normal way" since seachers
: require a query. And I don't want a query with a wildcard term.

the bueaty of ConstantScoreQuery is that it can wrap any filter ... so you
can execute your Filter as a normal search, even without any other
"scoring" clauses to your query.

: a filter that aggregates the three clauses using WildcardTermEnum. I found
: the MatchAllQuery, and tried using that and passing it the filter I
: constructed to the searcher, something like...
: MatchAllDocsQuery(), mynewfilter);
: This is painfully slow. So I got clever and just iterated through the bitset

that method returns a Hits obejct correct? ... as mentioned many times
before, using the Hits class is not recommended when you are dealing with
more then then just the first 100 or so results of a search... i seem to
recall that you said your searches typically result in thousands of
documents, nad you need data from all of them correct?

use one of the methods that returns TopDocs (or TopFieldDocs).

: 1> Did I misuse/misunderstand MatchAllDocs? What's it for anyway if not
: this?

you understood it, i just don't think you need it in this case.  I also
dont' think it's really the cause of the speed differneces you saw, that's
most likely caused by the way the Hits class works (reexecuting your
search over and over as you iterate through the results)

: 2> Since all the terms have wildcards, I don't get ranking etc. anyway.
: right? So I'm not losing anything by messing with the bitset myself, right?

That's true.  in fact if you know that you are never going to want
ranking/scoring info, and if you know that you are allways going to be
using Filter classes (and never Query classes) then there's no reason not
to just call the Filter.bits(IndexReader) and then use the BitSet anyway
you see fit.

: 3> I should create a BooleanQuery (or equivalent) on any terms that do NOT
: have wildcards and pass the filter to the searcher in order to get some
: rankings/relevance. And one expects that to perform substantially better
: than using MatchAllDocs. Yes? No?

Hard to say ... the way Filters are currently implimented, they have no
means of 'skipping' documents that don't match the query.  so the amount
of time spent executing your Filter.bits method will be the same.  but the
other clauses will help eliminate documents during hte search (using
indexed fields which are fast), which will save you from ever seeing them
when you iterate over your TopDocs (so you'll never call the doc(i) method
on them, and never waste anytime with their stored fields which are slow)

: 4> In my specific case, I don't believe caching filters helps me because the
: chances of any of my search terms being the same across requests is small.
: Given that, is there anything but convenience to using a ChainedFilter? In
: my crude testing, I just declared another bitset, populated it and then
: anded/ored/andnoted it to the bitset returned from my filter. Don't worry,
: I'm going to chain them, I'm just checking my understanding.

ChainedFilter is certainly there for convincience.  if there is
notadvantage to you (caching or otherwise) to keeping the various bits of
logic you've got in seperate Filters, then there's no reason to use
ChainedFilter ... jsut combine all of hte logic into one Filter.

(this has hte added bonus of only ever needing to allocate one huge
BitSet, instead of anding/oring multiple big BitSets.)


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