Whether Oracle uses partition pruning is reflected in the execution plan of a statement, either in the plan table for the EXPLAIN PLAN statement or in the shared SQL area.
The partition pruning information is reflected in the plan columns PSTART (PARTITION_START) and PSTOP (PARTITION_STOP). For serial statements, the pruning information is also reflected in the OPERATION and OPTIONS columns.
See Also:
Oracle Database SQL Tuning Guide for more information about EXPLAIN PLAN and how to interpret it