13.3.4 Implementing Transparent Application Failover

Depending on the FAILOVER_MODE parameters, you can implement TAF in several ways. Oracle recommends these methods.

Important:

Do not set the GLOBAL_DBNAME parameter in the SID_LIST_listener_name section of the listener.ora file. A statically configured global database name disables TAF.

• TAF with Connect-Time Failover and Client Load Balancing
  Implement TAF with connect-time failover and client load balancing for multiple addresses.
• TAF Retrying a Connection
  TAF enables you to automatically retry connecting if the first connection attempt fails with the RETRIES and DELAY parameters.
• TAF Pre-establishing a Connection
  TAF enables you to pre-establish a backup connection. You must explicitly specify the initial and backup connections.

13.3.4.1 TAF with Connect-Time Failover and Client Load Balancing

Implement TAF with connect-time failover and client load balancing for multiple addresses.

In the following example, Oracle Net connects randomly to one of the protocol addresses on sales1-server or sales2-server. If the instance fails after the connection, then the TAF application fails over to the other node's listener, reserving any SELECT statements in progress.

sales.us.example.com=
 (DESCRIPTION=
  (LOAD_BALANCE=on) 
  (FAILOVER=on) 
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales1-server)  
       (PORT=1521)) 
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales2-server)  
       (PORT=1521)) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (FAILOVER_MODE=
       (TYPE=select) 
       (METHOD=basic))))

Although the preceding example has multiple addresses, the optional ADDRESS_LIST parameter is not used.

13.3.4.2 TAF Retrying a Connection

TAF enables you to automatically retry connecting if the first connection attempt fails with the RETRIES and DELAY parameters.

In the following example, Oracle Net tries to reconnect to the listener on sales1-server. If the failover connection fails, then Oracle Net waits 15 seconds before trying to reconnect again. Oracle Net attempts to reconnect up to 20 times.

sales.us.example.com=
 (DESCRIPTION=
  (ADDRESS=
       (PROTOCOL=tcp)  
       (HOST=sales1-server)  
       (PORT=1521)) 
  (CONNECT_DATA=
     (SERVICE_NAME=sales.us.example.com) 
     (FAILOVER_MODE=
       (TYPE=select) 
       (METHOD=basic)
       (RETRIES=20)
       (DELAY=15))))

13.3.4.3 TAF Pre-establishing a Connection

TAF enables you to pre-establish a backup connection. You must explicitly specify the initial and backup connections.

In the following example, clients that use network service name sales1.us.example.com to connect to the listener on sales1-server are also preconnected to sales2-server. If sales1-server fails after the connection, then Oracle Net fails over to sales2-server, preserving any SELECT statements in progress. Similarly, Oracle Net preconnects to sales1-server for those clients that use sales2.us.example.com to connect to the listener on sales2-server.

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