Data Guard

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Oracle Data Guard can be deployed to maintain standby databases at a secondary site. These standby databases are maintained as synchronized copies of the production database.

If the production database becomes unavailable because of a planned or an unplanned outage, Data Guard can switch the standby database to the production role, thus minimizing the downtime associated with the outage, and preventing any data loss.


[edit] History

The ability to create standby databases was first offered as a feature in Oracle 8i, although users were creating manual standby databases since Oracle 7.3.

Features introduced in Oracle 8i:

  • Read-only physical standby database
  • Managed recovery of standby
  • Remote archiving of redo log files

Features introduced in Oracle 9i:

  • Integrated zero-data-loss capability
  • Data Guard Broker w/ Data Guard Manager GUI
  • Command Line Interface (CLI)
  • Switchover and Failover operations
  • Automatic gap resolution
  • Automatic Synchronization
  • Logical standby databases
  • Maximum protection / availability
  • Enhanced Data Guard Broker
  • Cascaded redo log destinations

Features introduced in Oracle 10g:

  • Real-time apply
  • Recovery through OPEN RESETLOGS
  • Simplified configuration with VALID_FOR attribute
  • Standby redo log support on logical standby databases
  • Improved redo transmission security
  • Improved support for RAC
  • Zero downtime instantiation of logical standby databases
  • Fast-start Failover
  • Flashback Database across Data Guard switchovers
  • Asynchronous Redo Transmission
  • Faster Redo Apply failover

Features introduced with Oracle 11g:

  • Standby databases can remain open while doing recovery
  • Heterogeneous platform support (standby can be on a different platform). For example, production on Linux and standby on Windows.

[edit] Licensing

Data guard technology ships with the Oracle database server. Enterprise edition licenses are required for ALL of the primary and standby database servers.

[edit] Advantages offered

  • Data Guard provide high availability for database servers
  • Reduces the amount of human intervention required to switch between sites
  • There is no distance limitation - the secondary site can be located thousands of kilometres away.

[edit] Implementation

Oracle provides both GUI and command-line tools for managing Data Guard configurations.

With appropriately set up, DBAs can facilitate failovers or switchovers to alternative hosts in alternative locations.

[edit] Also see