Oracle Parallel Processing

Managing Instance Groups

You can logically group instances of an OPS database into multiple instance groups. You do this by setting the INSTANCE_GROUPS parameter in the initialization parameter file. The INSTANCE_GROUPS parameter defines instance groups and assigns an instance to them. For example, when you specify the following INIT.ORA parameter for an instance, that instance will belong to groupA:

INSTANCE_GROUPS = groupA

One instance can belong to multiple instance groups at the same time. The INSTANCE_GROUPS parameter specifies the group names using a comma-separated list—for example:

INSTANCE_GROUPS = groupA, groupB

With this setting, the instance will be in groupA as well as in groupB.

The instances belonging to a particular instance group can be determined by referring to the INIT.ORA files of all the instances. Let’s consider an OPS configuration with four instances having the settings shown in Table 7.2.

Table 7-2. INSTANCE_GROUPS Settings for a Four-Instance Configuration

Instance	INSTANCE_GROUPS Setting
1	g12, g14, g123
2	g12, g23, g123
3	g23, g123
4	g14

The settings shown in Table 7.2 define four instance groups—g12, g14, g123, and g23 in the system—and assign instances to groups as specified. Instance group g12 is specified in the initialization parameter files of instances 1 and 2. Therefore, instance group g12 consists of those two instances. Group names do not need to reflect the instance numbers. We could have used any arbitrary name in place of g12.

Instance ...