Data GUARD Configurations:

A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can COMMUNICATE with each other.

 Dataguard Architecture

The Oracle 9i Data Guard architecture incorporates the following items:

• Primary Database – A production database that is used to create standby databases. The archive logs from the primary database are transfered and applied to standby databases. Each standby can only be associated with a single primary database, but a single primary database can be associated with multiple standby databases.
• Standby Database – A replica of the primary database.
• Log Transport SERVICES – Control the automatic transfer of archive redo log files from the primary database to one or more standby destinations.
• Network Configuration – The primary database is connected to one or more standby databases using Oracle Net.
• Log Apply Services – Apply the archived redo logs to the standby database. The Managed Recovery Process (MRP) actually does the work of maintaining and applying the archived redo logs.
• Role Management Services – Control the changing of database roles from primary to standby. The services include switchover, switchback and failover.
• Data Guard Broker – Controls the creation and monitoring of Data Guard. It comes with a GUI and command line interface.

Primary Database:

A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.

Standby Database:

A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to nine standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.

The types of standby databases are as follows:

Physical standby database:

Provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. A physical standby database is kept synchronized with the primary database, through Redo Apply, which recovers the redo data received from the primary database and APPLIES the redo to the physical standby database.

Logical standby database:

Contains the same logical information as the production database, although the physical ORGANIZATION and structure of the data can be different. The logical standby database is kept synchronized with the primary database through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database.

Data Guard Configurations:

A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other.

 Dataguard Architecture

The Oracle 9i Data Guard architecture incorporates the following items:

Primary Database:

A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.

Standby Database:

A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to nine standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.

The types of standby databases are as follows:

Physical standby database:

Provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. A physical standby database is kept synchronized with the primary database, through Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database.

Logical standby database:

Contains the same logical information as the production database, although the physical organization and structure of the data can be different. The logical standby database is kept synchronized with the primary database through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database.