A great way to limit CPU on a shared database server is by using instance caging, below are the steps to implement instance caging.

1. Check to see if instance caging is enabled

SQL> select name from v$rsrc_plan where is_top_plan = 'TRUE' and cpu_managed='ON';
no rows selected

Its not enabled

2. Set the CPU count

Set the cpu_count to what figure your require to limit the CPU in the instance to

SQL> alter system set cpu_count = 4;
System altered.

3. Enable instance caging

SQL> alter system set resource_manager_plan = 'default_plan';
System altered.

4. Check to see if instance caging is enabled

SQL> select name from v$rsrc_plan where is_top_plan = 'TRUE' and cpu_managed='ON';
NAME
--------------------------------
DEFAULT_PLAN

You have now enabled instance caging limiting your database to a maximum of 4 cpu’s to use