Type : Integer
Default : None
Modify : No
Range : 1 or >= the number of instances in the cluster. (Values other than 1
have no effect on the active or standby status of any instances.)
Basic : No
RAC : You must set this parameter for every instance, and multiple instances
must have the same value.

Notes : ACTIVE_INSTANCE_COUNT enables you to designate one instance in a two-instance cluster as the primary instance and the other instance as the secondary instance. This parameter has no functionality in a cluster with more than two instances. When you set this parameter to 1, the first instance you start up becomes the primary instance and accepts client connections. The second instance starts up as a secondary instance and can accept client connections only if the first instance fails. In such an event, the secondary instance becomes the primary instance. When the failed instance can once again be started up, it starts up as the secondary
instance, and will not accept client connections unless the current primary instance fails.