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From: Apache Wiki <wikidiffs@apache.org>
To: java-commits@lucene.apache.org
Date: Mon, 08 Jun 2009 01:46:12 -0000
Message-ID: <20090608014612.8909.34634@eos.apache.org>
Subject: [Lucene-java Wiki] Update of "Lincolm" by Lincolm

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The following page has been changed by Lincolm:
http://wiki.apache.org/lucene-java/Lincolm

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  Lucene HitCollector implementation with FieldCache to create document categorized searches with minimal impact to performance.
+ 
+ When creating a lucene search application, one commom problem is create a categorized search with groupings count based on that categories. Suppose you want a search grouping documents found by a specific criteria. You have a list of articles, this articles has several fields (title, body, theme, date, keywords, and on). Now, you want to create a search over this articles list (materialized do a lucene index) and the search result must show a grouping count for every article found on every theme for all document set.
+ 
+ Using some specialization to default HitCollector implementation can be easily done, and will allow you to iterate over all document set. Iterate over all document set has a cost, but, in this case it's necessary due search requisit: create grouping counts for every theme found in a given search.
+ 
+ Access the disk, same using a FieldSelector it's not the best way because increase search response time due much more IO activity to read documents on index. One efficient way I found was iterate over all document set, but, instead of read all document from index (even using a FieldSelector), I read the theme information from FieldCache implementation. So, the query runs faster because no IO access is necessary!
+ 
+ Another problem I found was if an article has a multivalued field. The default FieldCache implementation returns the first field value, only. So, I created a specialized FieldCache in which a store the multivalued field as TermFreqVector.YES and I used IndexReader.getTermFreqVector(doc) to read back the field array. During searcher creation  - new IndexSearcher(reader) - I populate this special FieldCache and I used it directly from my HitCollector.
+ 
+ My application is running on production environment since 01/Jan/2009 at address: http://www.clicrbs.com.br/busca/rs (portuguese site). So, a sample searching, grouping and creating paging can be found like this: http://www.clicrbs.com.br/busca/rs?c=-1&debug=true&q=tipo%3Amaterias&t=2009
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