Oracle Data Guard Broker is a centralized framework that automates the configuration, management, and monitoring of an Oracle Data Guard configuration. Oracle Data Guard Broker further enhances Oracle RAC by providing apply instance failover for Oracle RAC standby databases. If your apply instance fails, the broker automatically starts recovery on a surviving instance. With Oracle Database 11g Release 2, seamless database role transitions are now possible with its integration of Oracle Clusterware.
The Oracle Data Guard Broker can be accessed locally or remotely by using either of the two clients: the command line interface (DGMGRL) or the Oracle Data Guard page of Oracle Enterprise Manager (OEM). Once it’s configured, you can modify any attribute of the configuration, monitor the configuration, perform health checks, and perform role changes with a single command. Truly a wonderful thing.
Oracle Data Guard Broker architecture overview
The Oracle Data Guard Broker is a feature of the Oracle database that consists of two client interfaces (OEM and DGMGRL) and the Oracle Data Guard Monitor (DMON) process. The Oracle Data Guard OEM and DGMGRL interfaces allow you to monitor and manipulate the configuration. The DMON is a background process that runs on every database instance in the configuration. When you make a change via one of the two interfaces, the DMON process interacts with the database to effect the actual change. The DMON process also reports back on the health of the configuration. All of the information that the DMON process needs to maintain the configuration is stored in metadata files.
Oracle Data Guard Broker configuration
An Oracle Data Guard Broker configuration is a logical definition of an Oracle Data Guard configuration allowing for centralized management and configuration of the physical resources involved in the configuration. With 11g Release 2, an Oracle Data Guard Broker configuration will contain a single primary database and up to 30 standby databases. The standby databases can be any combination of physical, logical, or snapshot. The configuration may also contain combination of Oracle RAC or single-instance databases.
Once a broker configuration has been implemented, modification of the Oracle Data Guard attributes such as log apply services and protection levels should be managed using one of the Oracle Data Guard Broker clients (DGMGRL or OEM). If Oracle Data Guard attributes are modified outside the broker, this will cause an inconsistency between the broker configuration and the database configuration. In most cases, these inconsistencies are resolved on the next startup of the DMON process by overriding the database attributes with those stored in the broker configuration.