Using the parallel_automatric_tuning parameter

If you are using an SMP or MPP database server with many CPUs, you can issue a parallel request and leave it up to each Oracle instance to use its default degree of parallelism. For example, consider the following parallel query:



select /*+ FULL(employee_table)
PARALLEL(employee_table, DEFAULT, DEFAULT) */
employee_name
from
employee_table
where
emp_type = 'SALARIED';



Oracle also provides the parallel_automatic_tuning init.ora parameter to assist in setting the best degree of parallelism. When setting parallel_automatic_tuning, you only need to specify parallelism for a table, and Oracle will dynamically change the parallel_adaptive_multi_user parameter to override the execution plan in favor of maintaining an acceptable overall load on the database.



For additional details, see the Oracle Press Book “Oracle High Performance Tuning with STATSPACK”.