Index: src/java/org/apache/lucene/document/NumericField.java =================================================================== --- src/java/org/apache/lucene/document/NumericField.java (revision 814707) +++ src/java/org/apache/lucene/document/NumericField.java (working copy) @@ -107,6 +107,10 @@ * like to change the value. Note that you must also * specify a congruent value when creating {@link * NumericRangeQuery} or {@link NumericRangeFilter}. + * For low cardinality fields larger precision steps are good. + * If the cardinality is < 100, it is fair + * to use {@link Integer#MAX_VALUE}, which produces one + * term per value. * *

For more information on the internals of numeric trie * indexing, including the The default for all data types is 4, which is used, when no precisionStep is given. *

  • Ideal value in most cases for 64 bit data types (long, double) is 6 or 8. *
  • Ideal value in most cases for 32 bit data types (int, float) is 4. + *
  • For low cardinality fields larger precision steps are good. If the cardinality is < 100, it is + * fair to use {@link Integer#MAX_VALUE} (see below). *
  • Steps ≥64 for long/double and ≥32 for int/float produces one token * per value in the index and querying is as slow as a conventional {@link TermRangeQuery}. But it can be used * to produce fields, that are solely used for sorting (in this case simply use {@link Integer#MAX_VALUE} as * precisionStep). Using {@link NumericField NumericFields} for sorting * is ideal, because building the field cache is much faster than with text-only numbers. + * These fields have one term per value and therefore also work with term enumeration for building distinct lists + * (e.g. facets / preselected values to search for). * Sorting is also possible with range query optimized fields using one of the above precisionSteps. * *