Query optimization with statistics uses the collected statistics on the tables and indexes in a query to select an execution plan that can process the query in the most efficient manner. As a general rule, Oracle recommends that you collect statistics on your base table if you are interested in improving your query performance. Optimizing with statistics enables a more accurate estimation of the selectivity and costs of the CONTAINS predicate and thus a better execution plan.
The optimizer attempts to choose the best execution plan based on the following parameters:
The selectivity on the CONTAINS predicate
The selectivity of other predicates in the query
The CPU and I/O costs of processing the CONTAINS predicates
The following topics discuss how to use statistics with the extensible query optimizer.
Importing and exporting of statistics on ___domain indexes, including Oracle Text indexes, is not supported with the DBMS_STATS package. For more information on importing and exporting statistics, see the Oracle Database PL/SQL Packages and Types Reference.
Oracle Text Reference for information on the CONTAINS query operator