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From Raffaella Ventaglio <r.ventag...@gmail.com>
Subject Faceted search with OpenBitSet/SortedVIntList
Date Sat, 07 Feb 2009 18:57:19 GMT
Hi,

I am trying to implement a kind of faceted search using Lucene 2.4.0.

I have a list of configuration rules that tell me how to generate this
facets and the corresponding queries (that can range from simple term
queries to complex boolean queries).

When my application starts, it creates the whole set of facets objects and
initializes them.
For each facet:
- I create the query according to the configured rule;
- I ask the reader for the bitset corresponding to that query and I store it
in the Facet object;
- I get the cardinality of the bitset and I save it in the Facet object as
its "initial count".

When the user does a search I have to update the "counts" associated to each
Facet:
- I get the bitset corresponding to the "query + filter" generated by the
user search;
- I get the cardinality of the ("search bitset" AND "facet bitset") and I
save it as the updated count.


In my first solution, I used only "OpenBitSetDISI" objects, both for Facet
bitset and for search bitset.
So I could use "intersectionCount" method to get updated counts after user
search.

This works very well and it is very fast, but when the number of documents
in the index and the number of facets grows it is too memory consuming.


So I tried a different solution: when I create facet bitsets I use the same
rule applied in ChainedFilter/BooleanFilter to decide if I have to store an
OpenBitSet or a SortedVIntList.
When I have to calculate updated counts:
- if the facet has an OpenBitSet, I use the "intersectionCount" method
directly;
- if the facet has a SortedVIntList, I first create a new OpenBitSetDISI
using the SortedVIntList.iterator and then I use the "intersectionCount"
method.

In this way, I use a smaller amount of memory at initialization time, but
for each user search I create a large number of objects (that I suddenly
throw away) and this affects application performance because it wastes a lot
of time doing GC.

So my question is: is there a better way to accomplish this task?

I think, it would be fine if I could calculate "intersectionCount" directly
on SortedVIntList objects, but I have not found nothing like that in Lucene
2.4 JavaDoc.
Am I missing something?


As a reference, now my index contains more than 500.000 documents and I have
to create/manage up to 50.000 facets.
Using "second solution", at initialization time my facets structure requires
more or less 120MB (and this is good enough), while updating counts it uses
even 2GB of memory (and this is very bad).

Thanks in advance,
Raf

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