Oracle Data Guard: Difference between revisions

Revision as of 20:04, 11 June 2009

Revision as of 20:12, 11 June 2009

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A physical standby database replicates the exact contents of its primary database across the [[Oracle Net]] [[network layer]]. While the physical storage locations can be different, the data in the database will be exactly the same as the primary database. It 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).

=== Logical standby (SQL Apply) ===

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.

Logical standby databases re-apply SQL transactions generated on their primary node; thus physical structures and organization. As of Oracle release 11g Data Guard may operate across different "CPU architectures, operating systems ... operating system binaries (32-bit/64-bit), and Oracle database binaries (32-bit/64-bit)."<ref>http://download.oracle.com/docs/cd/B28359_01/server.111/b28294/standby.htm#insertedID3 ''Data Guard Concepts and Administration'', 11g Release 1 (11.1); Section 2.3.1 "Hardware and Operating System Requirements" Retrieved [[2007-10-01]]</ref> Users (under certain conditions) can write to as well as read from logical standby databases; and such databases can switch in function to and fro between primary and standby roles.

=== Active Data Guard ===