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Oracle Parallel Processing by Sanjay Mishra, Tushar Mahapatra

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Chapter 12. Application Failover

For many applications, the cost of having a database be unavailable is enormous. For applications used in the banking and brokerage industry, for example, the cost of database downtime can exceed a million dollars per hour. Consequently, backup databases often are used to provide protection against the failure of a primary database.

When a primary database instance fails, applications connected to the instance will receive an error indicating a lost connection. Not only do those user connections to the database get lost, but their uncommitted transactions also get lost. Users then are forced to reestablish a connection to the backup database and resubmit their transactions. This creates a lot of work disruption. The process of automatically switching an application from the primary database to a backup database is referred to as application failover. The objective of application failover is to minimize work disruptions as much as possible by transparently reconnecting to the backup database.

Often, an Oracle Parallel Server database is used to support application failover. In an OPS environment, when one or more Oracle instances fails, applications still can access the shared database through one of the surviving instances. Other approaches to failover include the use of standby databases and replicated databases. Although the focus in this chapter is on application failover in an OPS environment, we’ll talk briefly about these other approaches ...

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