The default behaviour is for the database to start tracing an operation only if it is sufficiently expensive.

• SQL Statement that runs in parallel
• SQL Statement that takes more than 5 seconds of CPU or I/O time.

You can however override this by doing the following

• Using the /*+ MONITOR */ hint within any SQL statement
• Set FORCED_TRACKING attribute to Y when using the DBMS_SQL_MONITOR.BEGIN_OPERATION function.

NOTE: The following 2 parameters must also be set (These are currently default in 12cR1)

• STATISTICS_LEVEL = TYPICAL (or ALL)
• CONTROL_MANAGEMENT_PACK_ACCESS = DIAGNOSTICS+TUNING