Oracle Data Guard: Difference between revisions

Revision as of 03:30, 5 September 2007

Revision as of 00:59, 1 October 2007

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Oracle Corporation provides both [[graphical user interface|GUI]] and [[command line interface|command-line]] tools for managing Data Guard configurations.

Data Guard supports both '''physical standby''' and '''logical standby''' sites. ItOracle runsCorporation undermakes mostData OracleGuard editions,available butonly notas undera Oracle[[product Expressbundling | bundled]] feature included within its "Enterprise Edition" (XE)of the [[Oracle RDBMS]]. <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 2.3.2: "Oracle Software Requirements" Retrieved [[2007-10-01]]

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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.

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== 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 in both modes 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. UsersAs (ifof grantedOracle permissions)release can11g writeData toGuard themmay asoperate wellacross asdifferent read"CPU fromarchitectures, them;operating andsystems such... databasesoperating cansystem switchbinaries in function to(32-bit/64-bit), and froOracle betweendatabase primarybinaries and standby roles(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]]

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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.

== Operation ==

A primary site which has an archived [[redo log]] to transfer invokes the '''RFS (remote file server)''' background process within the Oracle instance running on a standby host. The RFS process then performs the task of receiving archived redo logs sent from the primary database.

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>

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Once the archived redo logs have arrived, other processes (such as an '''ARCH (Archiver process)''', an '''MRP (Managed Recovery Process)''', and/or an '''LSP (Logical Standby Process)''') may set about applying theirthe log contents to the standby database..

== 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 | disaster-recovery]] ("failover") or [[upgrade]]/[[maintenance]] ("switchover") time.

== References ==