Parallel Query

This is a good link:http://www.oracle.com/technology/oramag/oracle/05-may/o35dba.html

when tables are created with degrees > 1 Oracle can assume a parallel execution plan of a large query.

In the plan you can see this by PX

Its a good idea to have the parameter parallel_automatic_tuning set to TRUE.

To disable parallel query use no_parallel hint./* no_parallel(T1) no_paralle(T2) */

Use the table aliases as in the query.