Oracle Data Guard

The software which Oracle Corporation markets as Oracle Data Guard forms an extension to the Oracle relational database management system (RDBMS). It aids in establishing and maintaining secondary standby databases as alternative/supplementary repositories to production primary databases.

Oracle provides both graphical user interface (GUI) and command-line (CLI) tools for managing Data Guard configurations.

Data Guard supports both physical standby and logical standby sites. Oracle Corporation makes Data Guard available only as a bundled feature included within its "Enterprise Edition" of the Oracle RDBMS.

With appropriately set-up Data Guard operations, DBAs can facilitate failovers or switchovers to alternative hosts in the same or alternative locations.

For the purposes of Data Guard, each Oracle database functions either in a primary database role or in a standby database role - with the ability to transition from one role to the other.

A physical standby database replicates the exact contents of its primary database across the Oracle Net network layer. While the relative physical storage locations can differ, the data in the database will be exactly the same as in the primary database. Physical standby databases can function either in managed-recovery mode or in read-only mode, but not in both modes at the same time (unless the databases are at Oracle Database 11.1 or higher and the Active Data Guard option is licensed - see below). The standby makes use of "Redo Apply" technology.

Physical standby databases have the same DBID identifiers as their primary equivalents.

Logical standby databases convert the redo generated at the primary database into data and SQL and then re-apply those SQL transactions on the logical standby. Thus, physical structures and organization will be different from the primary database. Users can read from logical standby databases while the changes are being applied and, if the GUARD is set to STANDBY (ALTER DATABASE GUARD STANDBY;), write to tables in the logical standby database that are not being maintained by SQL Apply.

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