13.4 Specifying the Instance Role for Primary and Secondary Instance Configurations

The INSTANCE_ROLE parameter is an optional parameter for the CONNECT_DATA section of a connect descriptor. It enables you to specify a connection to the primary or secondary instance of Oracle RAC configurations.

This parameter is useful when:

• You want to explicitly connect to a primary or secondary instance. The default is the primary instance.

• You want to use TAF to preconnect to a secondary instance.

Table 13-5 describes the INSTANCE_ROLE parameters.

Table 13-5 INSTANCE_ROLE Parameters

INSTANCE_ROLE Parameter	Description
PRIMARY	Specifies a connection to the primary instance.
SECONDARY	Specifies a connection to the secondary instance.
ANY	Specifies a connection to whichever instance has the lowest load, regardless of primary or secondary instance role.

Connection to Instance Role Type

In the following example of the tnsnames.ora file, network service name sales_primary enables connections to the primary instance, and network service name sales_secondary enables connections to the secondary instance.

sales_primary=
 (DESCRIPTION=
  (ADDRESS_LIST=
    (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales1-server)  
       (PORT=1521)) 
    (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales2-server)  
       (PORT=1521))) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (INSTANCE_ROLE=primary)))
sales_secondary=
 (DESCRIPTION=
  (ADDRESS_LIST=
    (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales1-server)  
       (PORT=1521)) 
    (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales2-server)  
       (PORT=1521))) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (INSTANCE_ROLE=secondary)))

Connection to a Specific Instance

There are times when Oracle Enterprise Manager Cloud Control and other system management products need to connect to a specific instance regardless of its role to perform administrative tasks. For these types of connections, configure (INSTANCE_NAME=instance_name) and (INSTANCE_ROLE=any) to connect to the instance regardless of its role.

In the following example, network service name sales1 enables connections to the instance on sales1-server and sales2 enables connections to the instance on sales2-server. (SERVER=dedicated) is specified to force a dedicated server connection.

sales1=
 (DESCRIPTION=
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales1-server)  
       (PORT=1521)) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (INSTANCE_ROLE=any)
     (INSTANCE_NAME=sales1)
     (SERVER=dedicated)))
sales2=
 (DESCRIPTION=
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales2-server)  
       (PORT=1521)) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (INSTANCE_ROLE=any)
     (INSTANCE_NAME=sales2)
     (SERVER=dedicated)))

Note:

Failover is incompatible with the preceding settings.

TAF Pre-establishing a Connection

If TAF is configured, then a backup connection can be pre-established to the secondary instance. The initial and backup connections must be explicitly specified. In the following example, Oracle Net connects to the listener on sales1-server and preconnects to sales2-server, the secondary instance. If sales1-server fails after the connection, then the TAF application fails over to sales2-server, the secondary instance, preserving any SELECT statements in progress.

sales1.example.com=
 (DESCRIPTION=
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales1-server)  
       (PORT=1521)) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (INSTANCE_ROLE=primary) 
     (FAILOVER_MODE=
       (BACKUP=sales2.example.com) 
       (TYPE=select)
       (METHOD=preconnect))))
sales2.example.com=
 (DESCRIPTION=
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales2-server)  
       (PORT=1521)) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (INSTANCE_ROLE=secondary)))