http://lmgtfy.com/?q=oracle+rac+instance+groups+parallel+query+affinity See the first result from above search. But, basically, if you want to restrict all parallel query activity to a specific node, then, on each node, set instance_groups to the instance name: inst1.instance_groups=inst1 inst2.instance_groups=inst2 etc,etc.... Then to run on instance inst1, do: Alter sesstion set parallel_instance_groups=inst1; Should be pretty straightforward. This is a simple example. Value of instance_groups can be set to any number of arbitrary identifiers, so, a specific group could span a certain subset of instances. See the paper for more detailed examples. -Mark From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of GBA-DBA Sent: Wednesday, June 10, 2009 12:11 PM To: Oracle Discussion List Subject: How to setup RAC to avoid Inter-Instance Parallelism Hello list, I have a two node 10.1.0.5 RAC setup serv1 - instance 1 serv2 - instance 2 We are using parallel query for batch processing. The time to complete batch is ok when we run in a non clustered environment (that's what we have in dev and integrated testing) but when we move the batch to a clustered testing environment similar to prod everything takes 2 or 3 times longer. I have noticed that some of the slave processes go to instance 1 and some of them go to instance 2. I would like to confine the parallel slaves to one instance but I don't fully understand how to setup the instance_groups and parallel_instance_groups to achieve this. Could anyone help me please? Thanks in advance. -- Regards GBA