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From mark harwood <>
Subject Re: performance on filtering against thousands of different publications
Date Mon, 13 Aug 2007 14:17:58 GMT
I would presume that (like a lot of things) there is power-law at play in the popularity of
publication sources (i.e. a small number of popular sources and a lot of unpopular ones).
The "Zipf" plugin in Luke can be used to illustrate this distribution for the values in your
"publication source" field.

Given this disparity, it makes sense to only cache Filters for the most popular publication
sources. Reading a large list of doc ids (the TermDocs) for these popular terms takes a lot
of time so it makes sense to cache them whereas it clearly is not valuable to use exactly
the same amount of memory (i.e. a new Bitset(reader.maxDoc) ) to cache an unpopular term whose
TermDocs can be read from disk quickly.
I would use BooleanFilter to combine the user's choices of publication source terms and use
CachingWrapperFilter around (popular) individual Term Filters added to the BooleanFilter rather
than using CachingWrapperFilter around the BooleanFilter as a whole. This is because your
are much more likely to get cache hits on the popular individual terms than on a user's particular
selection of publication sources and these cached items can be combined together in the BooleanFilter
super fast.

Hope this makes sense

----- Original Message ----
From: Cedric Ho <>
Sent: Monday, 13 August, 2007 5:17:52 AM
Subject: performance on filtering against thousands of different publications

Hi all,

My problem is as follows:

Our documents each comes from a different publication. And we
currently have > 5000 different publication sources.

Our clients can choose arbitrarily a subset of the publications while
performing search. It is not  uncommon that a search will have to
match hundreds or thousands of publications.

I currently try to index the publication information as a field in
each document. and use a TermsFilter when performing search. However
the performance is less than satisfactory. Many simple searches takes
more than 2-3 seconds. (our goal: < 0.5seconds).

Using the CachingWrapperFilter is great for search speed. But I've
done some calculation and figured that it is basically impossible to
cache all combination of publications or even some common

Is there any other more effective way to do the filtering?

(I know that the slowness is not purely due to the publication filter,
we also have some other things that will slow down the search. But
this one definitely contributed quite a lot to the overall search


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