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From Chris Hostetter <hossman_luc...@fucit.org>
Subject RE: PrefixQuery rewrite() bug, ignores max clause count
Date Mon, 17 Jul 2006 21:45:31 GMT

: I understand the concern for resources, but by throwing an exception you
: have also preempted a legitimate query.  How then should one go about
: performing a query for all document where a field begins with char X?

that's the rub .. the "legitimacy" of the query is based on the index it
is executed against, and the maxClauseCount configured for that app .. a
prefix query for b* may be perfectly legitimate in a small index, but very
very bad in another ... that's what that exception is warning you about:
for your index, and your current maxClauseCount configuration, that query
is not legal.

: IMHO, both your concern for resources and the ability to query for
: "name:b*" are legitimate.  Perhaps PrefixeQuery should be able to
: gracefully degrade when it hits resource limits.  I admit I am at the

this has been discussed before, and the crux of the issue is that by
throwing this exception, PrefixQuery (or any other query that rewrites to
a BooleanQUery) is giving you the information you need to make your app
degrade in whatever way you want (gracefull or otherwise).  In apps like
Solr, RangeQueries are by based completely to prevent this problem,
PrefixQueries could likewise be avoided ... i believe Nutch may acutally
have something like what you describe (where if a query cases a toomancy
clauses exception, it rewrites that clause into a filter)

: limit of my Lucene knowledge here, but I assume that rewrite() is an
: optimization of the query and can be skipped (with some additional code)
: at the cost of performance.

nope.  In Lucene, there are two types of queries: primative, and
non-primative.  Primative queries are query classes that can create
Weights/Scorers to execute them, non-primate queries are just containers
that make it easy to model a particular type of search, but in the context
of particular index, "rewrite" themselves into primative queries.
(primative queries rewrite to themselves).  a PrefixQuery *must* rewrite
itself into a BooleanQuery containing one TermQuery for each term in the
index matching that prefix.

: We do not rank or score results at all (Lucene is a high speed index for
: us).  As a result, I am blissfully ignorant of scoring results.  Out of
: curiosity though, does the depth of a term in a query tree affect its
: score?

in a nut shell: yes.  not becuse "depth" really has any meaning to how
scoring works, but because the score produced by a boolean query when some
of it's clauses match depends on the number of clauses, so a boolean query
contaiing 10 terms scores differnetly then a boolean query cotaining 5
boolean queries each containing 2 term queries.



-Hoss


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