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Oracle Parallel Processing by Sanjay Mishra, Tushar Mahapatra

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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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