[Solr Wiki] Update of "SolrFacetingOverview" by DavidGreen

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The "SolrFacetingOverview" page has been changed by DavidGreen.
http://wiki.apache.org/solr/SolrFacetingOverview?action=diff&rev1=18&rev2=19

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  == FacetFields ==
  Any number of [[SimpleFacetParameters#facet.field|facet.field]] parameters can be passed to the request handler.  For each facet.field, one of two approaches will be used based on the [[SimpleFacetParameters#facet.method|facet.method]] or the field type:
  
-  * '''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.
+  * '''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. ([[http://www.nicetick.com/|Air Jordan 2]]). 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://hudson.zones.apache.org/hudson/job/Lucene-trunk/javadoc/all/org/apache/lucene/search/FieldCache.html|FieldCache]] or (starting in Solr 1.4) an !UnInvertedField if the field either is multi-valued or is tokenized (according to FieldType.isTokened()). 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.