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The following page has been changed by jeffnewburn:
http://wiki.apache.org/solr/SolrFacetingOverview

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      * '''Enum Based Field Queries''':  If {{{facet.method=enum}}} or the 
field is defined in the schema as boolean, then Solr will iterate over all of 
the indexed terms for the field, and for each term it will get a filter from 
the filterCache and calculate the intersection with the filter for the base 
query.  This is excellent for fields where there is a small set of distinct 
values.  The average number of values per document does not matter.  For 
example, faceting on a field with U.S. States e.g. `Alabama, Alaska, ... 
Wyoming` would lead to fifty cached filters which would be used over and over 
again. The [:SolrCaching#filterCache:filterCache] should be large enough to 
hold all of the cached filters.
  
-     * '''Field Cache''': If {{{facet.method=fc}}} then a field-cache approach 
will be used.  This is currently implemented using either the the Lucene 
[http://lucene.apache.org/java/docs/api/org/apache/lucene/search/FieldCache.html
 FieldCache] or (starting in Solr 1.4) an !UnInvertedField if the field is 
multivalued or tokenized.  Each document is looked up in the cache to wee what 
terms/values it contains, and a tally is incremented for each value.  This is 
excellent for situations where the number of indexed values for the field is 
high, but the number of values per document is low.  For multi-valued fields, a 
hybrid approach is used that uses term filters from the filterCache for terms 
that match many documents.
+     * '''Field Cache''': If {{{facet.method=fc}}} then a field-cache approach 
will be used.  This is currently implemented using either the the Lucene 
[http://lucene.apache.org/java/docs/api/org/apache/lucene/search/FieldCache.html
 FieldCache] or (starting in Solr 1.4) an !UnInvertedField if the field is 
multivalued or tokenized.  Each document is looked up in the cache to see what 
terms/values it contains, and a tally is incremented for each value.  This is 
excellent for situations where the number of indexed values for the field is 
high, but the number of values per document is low.  For multi-valued fields, a 
hybrid approach is used that uses term filters from the filterCache for terms 
that match many documents.
  

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