The automatic indexing feature in Oracle Database is enabled in Autonomous Transaction Processing.
Creating indexes manually requires deep knowledge of the data model, application, and data distribution. Often DBAs make choices about which indexes to create, and then never revise their choices. As a result, opportunities for improvement are lost, and unnecessary indexes can become a performance liability.
With automatic indexing the database monitors the application workload, creating and maintaining indexes automatically. The indexing feature is implemented as an automatic task that runs at a fixed interval. You can use the
DBMS_AUTO_INDEX package to report on this automatic task and to set your preferences.
For more information see Managing Auto Indexes in Oracle Database Administrator’s Guide.