The recommended approach to gathering statistics is to allow Oracle to automatically gather the statistics.
Oracle gathers statistics on all database objects automatically and maintains those statistics in a regularly-scheduled maintenance job.
When you generate statistics for a table, column, or index, if the data dictionary already contains statistics for the object, then Oracle updates the existing statistics.
The older statistics are saved and can be restored later if necessary. When gathering statistics on system schemas, you can use the procedure .
If this feature is disabled, then the automatic statistics gathering job is not able to detect stale statistics.
This feature is enabled when the Automatic statistics gathering should be sufficient for most database objects which are being modified at a moderate speed.
to retain the space from the deleted rows allocated to the table.