One of the most important functions of the DBA is to provide for the continued availability of the information in the database. Prior to implementing the database, you need to specify how long you can afford to be down in the event of an emergency, as well as how long you can be down for normal maintenance. How you answer these questions determines what sort of redundancy you need to build into your configuration, and dictates how you will perform backups and standard system maintenance.

A number of Oracle facilities can help guarantee availability; we recommend that you consider the use of the replication, hot standby database, and Oracle Parallel Server facilities, described briefly in the following sections.