RAC Node Affinity with Parallel Instance Groups

A reader asks: 

Question: I want to load balance my RAC system, and I was considering using node affinity approach.  I also understand that RAC has a parallel instance groups feature for RAC balancing.  What are the advantages of each approach?

The expert says:

Answer: There are several approaches to partitioning a RAC cluster with the most popular being functional load balancing, which involves dedicating like-minded transactions to the same node.  The process of assigning specific users and transactions to specific RAC instances is called instance affinity.

The main approaches are:

1.    RAC Instance Affinity

2.    RAC CPU Processor Affinity

3.    RAC Parallel Instance Groups

The use of parallel instance groups allows control over which instances allocate parallel execution server processes with instance groups. Each active instance can be assigned to at least one or more instance service groups. By activating a particular service group of instances, the instances that spawn parallel processes can be dynamically controlled.

Instance group membership can be established on an instance-by-instance basis by setting the instance_groups initialization parameter to a name representing one or more instance groups.

Follow the link below for further insights on RAC node affinity with parallel instance groups:


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