apply instance

In an Oracle Real Application Clusters (Oracle RAC) databases environment, the apply instance is the one instance applying archived redo data to a standby database.


A distributed management framework that automates and simplifies most of the complex operations required to create, control, and monitor an Oracle Data Guard configuration.

broker configuration

A logical grouping of the primary and standby databases (including redo transport services and log apply services) of an Oracle Data Guard configuration.

See also Data Guard configuration.

bystander standby database

A standby database that is not the target of, or directly involved in, a switchover or failover operation.

configuration object

A named collection of database objects. It is an abstraction of an Oracle Data Guard configuration.

database guard

The database guard controls whether or not modifications can be made to the tables in a logical standby database.

database object

A named object that corresponds to a primary or standby database in an Oracle Data Guard configuration. The broker uses this object to manage and control the state of a single database and to associate properties with the database.

Data Guard command-line interface

The Oracle Data Guard command-line interface (DGMGRL) enables you to control and monitor an Oracle Data Guard configuration from the DGMGRL prompt or within scripts.

Data Guard configuration

A distributed computing system that prevents or minimizes losses due to unplanned events (for example, human errors, environmental disasters, or data corruption) as well as to planned downtime (such as for routine maintenance tasks).

See also broker configuration.

Data Guard environment

The physical configuration of the primary, standby databases, and far sync instances. The environment depends on many factors, including the:

  • Number of standby databases and far sync instances associated with a primary database

  • Number of host systems used by the databases

  • Directory structures of the machines used by the databases

  • Network configuration

  • Redo transport services

  • Log apply services

The Oracle Data Guard environment can be managed manually by a DBA, automatically using Enterprise Manager or the Data Guard command-line interface (DGMGRL) or a combination of all of these.

default state

The initial runtime state in which the database object will run when you enable broker management of the configuration. The actual default state can vary depending on the role (primary or standby) in which the database is running.

See also intended state.


Failover changes a standby database into the role of a primary database and disables the old primary database.

See also fast-start failover and manual failover.

far sync instance

A remote Oracle Data Guard destination that accepts redo from the primary database and redistributes that redo throughout the Oracle Data Guard configuration. It is similar to a physical standby database in that it manages a control file, receives redo into Standby Redo Logs (SRLs), and archives those SRLs to local Archived Redo Logs (ARLs). But unlike a standby database, a far sync instance does not manage data files, cannot be opened for access, and cannot run redo apply.

fast-start failover

Enables a failover automatically when the primary database becomes unavailable. When fast-start failover is enabled, the broker determines if a failover is necessary and automatically, quickly, and reliably fails over to a designated standby without requiring that you perform any manual steps to invoke the failover.

See also manual failover.

instance object

A named object; a database object is a collection of one or more named instance objects. The broker uses this object to manage and control the state of the database with which the instance is associated, and to associate instance-specific properties with this instance of the database.

intended state

The runtime state of a database object while it is enabled for management by the broker.

See also default state.

lights out computing

Refers to computing equipment or software whose operations are automated, requiring little to no intervention by human administrators.

The term "lights out" originated from when computing centers were located in one room and contained a number of servers that were kept under lock and key and in the dark. Under normal operation, the room was not entered by human administrators, and all operations in the room were automated.

logical standby database

A logical standby database takes standard Oracle archived redo log files, transforms them back into SQL transactions, and then applies them to an open standby database. Although changes can be applied concurrently with end-user access, the tables being maintained through regenerated SQL transactions allow read-only access to users of the logical standby database. Because the database is open to allow application of reconstructed SQL transactions, it is physically different from the primary database. The database tables can have different indexes and physical characteristics from their primary database peers, but the tables must maintain logical consistency from an application access perspective, to fulfill their role as a standby data source.

manual failover

A failover that is initiated by the DBA who first determines a failover is necessary and then invokes one by clicking FAILOVER in Enterprise Manager or by issuing the DGMGRL FAILOVER command. The word manual is used to contrast this type of failover with a fast-start failover.

See also fast-start failover.


A DGMGRL client that continuously monitors the primary and target standby databases, evaluates whether failover is necessary, and initiates a fast-start failover when conditions warrant.

physical standby database

A physical standby database is an exact copy of a primary database. While the primary database is open and active, a physical standby database uses Redo Apply to apply redo data received from the primary database. Redo Apply can run on a physical standby database instance that is mounted. If a license for the Oracle Active Data Guard option has been purchased, Redo Apply can also run on a physical standby database instance that is open. See Oracle Data Guard Concepts and Administration for more details.

primary database

A production database from which one or more standby databases is created and maintained. Every standby database is associated with one and only one primary database. A single primary database can, however, support multiple standby databases. The Oracle Data Guard broker monitor (DMON) maintains the master copy of the binary configuration file with the primary database, ensuring that each standby database's copy of the file is kept up to date as changes are made.

The broker refers to this database using the value in the DB_UNIQUE_NAME initialization parameter which is defined to be globally unique.

read-only mode

A mode in which a database can be opened that allows queries, but disallows modifications.

A physical standby database can be opened read-only so that queries may be performed. If a license for the Oracle Active Data Guard option has been purchased, a physical standby database can be open while Redo Apply is active. This capability is known as real-time query. See Oracle Data Guard Concepts and Administration for more details.

Redo Apply

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.


Reinstatement is the process of turning a database, including the old primary database, that had been disabled after a failover operation into a viable standby database for the new primary database. Flashback database must be enabled on a database in order to reinstate it.

snapshot standby database

A snapshot standby is a fully updatable standby database that is created from a physical standby database. On snapshot standby databases, redo data is received but not applied until the snapshot standby database is converted back to a physical standby database.

SQL Apply

A 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.

standby database

A copy of a primary database created using a backup of your primary database. Standby databases are kept synchronized with the primary database by applying archived redo data over time from the primary database to each standby database. The standby database can take over processing from the primary database, providing nearly continuous database availability. A standby database has its own server parameter file, control file, and data files. It also has a copy of the broker's configuration file, kept up to date at the direction of the DMON process running in the primary database instance.

The broker refers to a standby database by its globally unique name that is stored in its DB_UNIQUE_NAME initialization parameter.

See also logical standby database, physical standby database and snapshot standby database.