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