Glossary

broker

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

broker configuration

A hierarchical and logical grouping of the sites and database resources (including log transport services and log apply services) in a Data Guard configuration.

See also Data Guard configuration.

bystander

A standby site including its database that is configured in a Data Guard configuration when a failover or switchover operation occurs, but is not involved in the role transition. That is, a bystander retains its standby role throughout the failover or switchover operation. Management of a bystander and its associated standby database can be enabled or disabled, and its state can be set to online or offline.

configuration object

A named collection of sites and the resource objects that those sites contain. It is an abstraction of an actual Data Guard configuration.

database resource object

A named object that corresponds to a primary or standby database instance. The broker uses this object to manage and control the state of a single database and to associate properties with the database.

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 and standby databases. The environment depends on many factors, including the:

Number of standby databases associated with a primary database
Number of host machines used by the databases
Directory structures of the machines used by the databases
Network configuration
Log transport services
Log apply services

The standby database environment can be managed manually by a DBA, automatically using Data Guard Manager or the Data Guard CLI, or a combination of all of these.

default state

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

See also intended state.

failover

Failover changes one of the standby sites and its databases into the role of primary site and primary database.

intended state

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

See also default state.

logical standby database

A logical standby database takes standard Oracle archived redo logs, 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, it is physically different from the primary database. The database tables can have different indexes, and physical characteristics from their primary database peers, but must maintain logical consistency from an application access perspective, to fulfill their role as a standby data source.

physical standby database

A physical standby database is physically identical to the primary database. While the primary database is open and active, a physical standby database is either performing recovery (by applying logs), or open for reporting access. A physical standby database can be queried read-only when not performing recovery while the production database continues to ship redo data.

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.

primary site

The location of the primary database. This is the site in a Data Guard configuration from which the database is available to applications and from where the data is shipped.

read-only mode

A physical standby database mode that is initiated using the following SQL statement:

ALTER DATABASE OPEN READ ONLY;

The read-only mode allows you to query a physical standby database, but does not allow you to make changes to it. While in this mode, redo logs are archived but are not applied until the physical standby database reenters managed recovery mode.

resource

A physical or logical component that is available to a computing system. Most commonly, a resource is an Oracle database server.

These resources are categorized by type and can include an Oracle database server resource and other services upon which these items depend. The various resource types are each separately managed on a given Data Guard configuration by a resource guard. Resource guards are registered with Data Guard broker during configuration.

resource guard

A component that acts as an interface between Data Guard broker and resources in a Data Guard configuration. Its jobs include registering resources with Data Guard broker, taking resources online and offline, reporting status for resources, translating parameter changes that affect resources, and conveying messages to resources.

site

A managed unit of failover in a Data Guard configuration. A database is replicated across a set of sites, one replicant per site. Dependent applications are instantiated on a site. When a site holding a primary role fails, another site holding the standby role transitions to the primary role and provides the desired service to users. Sites may be one of several types of nodes, which vary from one another in the degree of hardware complexity and software management.

site object

A named collection of database resource objects that reside on a single host.

standby database

A copy of a production database created using a backup of your primary database. Standby databases are kept synchronized with the primary database by applying archived redo logs 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 initialization parameter file, control file, and datafiles.

standby site

The location of the standby database. One or more server systems can serve as hosts for standby databases. The standby systems accept redo logs shipped from the primary site and apply changes to local copies of the database. The standby site can be on the same host system as the primary database or on a separate host system.