Oracle Data Guard: Difference between revisions

Revision as of 22:35, 25 August 2007

Revision as of 03:30, 5 September 2007

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With appropriately set-up Data Guard operations, [[database administrator|DBA]]s can facilitate [[failover]]s or [[switchover]]s to alternative hosts in the same or alternative locations.

== Configurations ==

A physical standby database attempts to replicate the exact structure and layout of its primary database across the Oracle Net network layer. It can function either in archiving ("recovery") mode or in read-only mode, but not both at the same time. It can become a standalone database when required, but needs rebuilding before reverting from standalone to standby functionality.

Logical standby databases re-apply SQL transactions generated on their primary node; thus physical structures and organization may differ. Users (if granted permissions) can write to them as well as read from them; and such databases can switch in function to and fro between primary and standby roles.

== Operation ==

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Alternatively, a supplementary mechanism may transfer the archived redo logs. On the standby database a '''Fetch Archive Log (FAL)''' client monitors for gaps in the sequence of received logs. If it finds a gap, it may invoke one or more Fetch Archive Log (FAL) servers to run on the primary database to forward the missing item(s).<ref>

[http://www.oracle-base.com/articles/9i/DataGuard.php Oracle-Base site summary of Data Guard], retrieved [[2007-09-05]]; [http://download.oracle.com/docs/cd/B28359_01/server.111/b28294/toc.htm Oracle Corp version 11.1 documentation links], retrieved [[2007-09-05]].

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== Advantages ==

Data Guard provides [[high availability]] for a database system. It can also reduce the human intervention required to switch between [[databases]] at disaster-recovery ("failover") or upgrade ("switchover") time.

== References ==