How to prevent Parallel slave process from spawning to other nodes?

In a RAC setup when parallel slave process spawns to other node it adversely impacts performance because of "GC BUFFER" wait events.

In order to prevent that you can use below :-

ON node 1 :-
ALTER SYSTEM SET instance_groups = 'rac01';
ALTER SESSION SET parallel_instance_groups = 'rac01';

ON node 2 :-
ALTER SYSTEM SET instance_groups = 'rac02';
ALTER SESSION SET parallel_instance_groups = 'rac02';

ON node 3 :-
ALTER SYSTEM SET instance_groups = 'rac03';
ALTER SESSION SET parallel_instance_groups = 'rac03';

ON node 4 :-
ALTER SYSTEM SET instance_groups = 'rac04';
ALTER SESSION SET parallel_instance_groups = 'rac04';