Oracle Tips by Burleson

10g Grid Computing with RAC
Real Application Cluster Architecture

tnsnames.ora File

Unless Oracle Names is used (or LDAP is used), each client and server that participates in the RAC environment must have a tnsnames.ora file. The tnsnames.ora file provides the local SQL*Net process a map to all available instances. The tnsnames.ora file also provides failover and load balance information. Failover is automatically set if a list of addresses is placed in the tnsnames.ora file, however, the failover method should be explicitly set using the failover_mode tnsnames.ora parameter.

A basic tnsnames.ora file for a load-balancing RAC setup is shown below:

TEST =
(DESCRIPTION =
(LOAD_BALANCE = ON)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = testlinux1)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = testlinux2)(PORT = 1521)))
(CONNECT_DATA =
(SERVICE_NAME = TEST))))
TEST1 =
(DESCRIPTION =
(ADDRESS_LIST =
(LOAD_BALANCE = ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = testlinux1)(PORT = 1521)))
(CONNECT_DATA =
(SERVICE_NAME = TEST)(INSTANCE_NAME = TEST1)))
TEST2 =
(DESCRIPTION =
(ADDRESS_LIST =
(LOAD_BALANCE = ON)
(ADDRESS = (PROTOCOL = TCP)(HOST = testlinux2)(PORT = 1521)))
(CONNECT_DATA =
(SERVICE_NAME = TEST)(INSTANCE_NAME = TEST2)))
EXTPROC_CONNECTION_DATA =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC)))
(CONNECT_DATA =
(SID=PLSExtProc)(PRESENTATION = RO)))
 
LISTENERS_TEST =
(ADDRESS = (PROTOCOL = TCP)(HOST = testlinux1)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = testlinux2)(PORT = 1521))

If a list of listener addresses is provided in the tnsnames.ora file, load balancing will be done automatically and there is no need to specify the load_balance parameters. They are shown here for example purposes only. The tnsnames.ora file provides the information needed to register the service names and instance-level information with the listener process. In addition, it specifies whether we desire load balancing and application failover, and specifies the method of failover, we desire. You can see that this is a very important file for RAC.

In addition to the access to the database and also to the specific instance, now users can access the Service directly by using the Virtual IP or Virtual IP host name. VIPCA (Virtual IP Configuration Assistant) helps to create services and associates the Virtual IP. Virtual IP is the public address through which a specific RAC database service can be accessed.