Failover Methods
Three methods are commonly used to implement application failover:
Connection-time failover using Net8
Transparent Application Failover (TAF) using Net8 and OCI8
Failover using a three-tier architecture
The failover methods discussed here are equally applicable to OPS environments, environments that use standby databases, and environments that use replicated databases as a basis for failover.
Connect-Time Failover with Net8
Connect-time failover refers to application failover when it occurs
during new connection attempts to a database. Using Net8, you can
configure a service so that if a connection to the primary database
is not successful, the connection is automatically routed to an
alternate database. Net8 configuration in support of connect-time
failover involves making appropriate entries in each client’s
tnsnames.ora file or in your Oracle Names
server. Because clients go through Net8 to connect to a database,
connect-time failover can be completely transparent to your
applications.
tnsnames.ora configuration
On client machines, Net8 uses a configuration file named
tnsnames.ora to translate a database service name into a specific hostname, port number, and instance name. When you connect to a service, Net8 reads this file to find out where that service resides. For any given service, you can define alternate database instances in order to implement connect-time failover. When you do this, any new connections to a service are first attempted using the first database ...
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