【转自MOS文章】把RAC当HA用的数据库参数

以下来源于：

Ora-12520/12516 Received When Listener on Node 1 is Down in RAC Setup. (文档 ID 357882.1)

ACTIVE_INSTANCE_COUNT set to 1 and primary instance is still running at the time of the test.
You have shutdown only the Listener so it leads to Ora-12516.

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.