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From Karl Wettin <karl.wet...@gmail.com>
Subject Re: Filters, what's going on under the hood?
Date Mon, 06 Apr 2009 19:53:56 GMT

6 apr 2009 kl. 15.47 skrev Lebiram:

> I am thinking of adding search filters to my application thinking  
> that they would more efficient.
>
> Can anyone explain what lucene does with search filters?
>
> Like, what generally happens when calling search()

A filter is a bitset, one bit per document in the index, used to tell  
Lucene to exclude these documents when processing the query. Generally  
it will only speed up your query if you can reuse the filter as it  
probably was created using the query it replaced.

This is what http://wiki.apache.org/jakarta-lucene/ 
ImproveSearchingSpeed says about filters:
	
Consider using filters.
It can be much more efficient to restrict results to a part of the  
index using a cached bit set filter rather than using a query clause.  
This is especially true for restrictions that match a great number of  
documents of a large index. Filters are typically used to restrict the  
results to a category but could in many cases be used to replace any  
query clause. One difference between using a Query and a Filter is  
that the Query has an impact on the score while a Filter does not.


       karl

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