A Data Guard configuration consists of one primary database and up to nine 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 if they can communicate with each other. For example, you can have a standby database on the same system as the primary database, along with two standby databases on another system.
The Data Guard broker logically groups these primary and standby databases into a broker configuration that allows the broker to manage and monitor them together as an integrated unit. You can manage a broker configuration using either the Oracle Enterprise Manager graphical user interface or the Data Guard command-line interface.
Oracle Data Guard Broker
The Oracle Data Guard broker is a distributed management framework that automates and centralizes the creation, maintenance, and monitoring of Data Guard configurations. The following list describes some of the operations the broker automates and simplifies:
- Creating Data Guard configurations that incorporate a primary database, a new or existing (physical or logical) standby database, redo transport services, and log apply services, where any of the databases could be Real Application Clusters (RAC) databases.
- Adding additional new or existing (physical or logical, RAC or non-RAC) standby databases to an existing Data Guard configuration, for a total of one primary database, and from 1 to 9 standby databases in the same configuration.
- Managing an entire Data Guard configuration, including all databases, redo transport services, and log apply services, through a client connection to any database in the configuration.
- Managing the protection mode for the broker configuration.
- Invoking switchover or failover with a single command to initiate and control complex role changes across all databases in the configuration.
- Configuring failover to occur automatically upon loss of the primary database, increasing availability without manual intervention.
- Monitoring the status of the entire configuration, capturing diagnostic information, reporting statistics such as the log apply rate and the redo generation rate, and detecting problems quickly with centralized monitoring, testing, and performance tools.
You can perform all management operations locally or remotely through the broker's easy-to-use interfaces: the Data Guard management pages in Oracle Enterprise Manager, which is the broker's graphical user interface (GUI), and the Data Guard command-line interface called DGMGRL.
These interfaces simplify the configuration and management of a Data Guard configuration.
Benefits of Data Guard Broker
The broker's interfaces improve usability and centralize management and monitoring of the Data Guard configuration. Available as a feature of the Enterprise Edition and Personal Edition of the Oracle database, the broker is also integrated with the Oracle database and Oracle Enterprise Manager. These broker attributes result in the following benefits:
Disaster protection: By automating many of the manual tasks required to configure and monitor a Data Guard configuration, the broker enhances the high availability, data protection, and disaster protection capabilities that are inherent in Oracle Data Guard. Access is possible through a client to any system in the Data Guard configuration, eliminating any single point of failure. If the primary database fails, the broker automates the process for any one of the standby databases to replace the primary database and take over production processing. The database availability that Data Guard provides makes it easier to protect your data.
Higher availability and scalability with Real Application Clusters (RAC) Databases: While Oracle Data Guard broker enhances disaster protection by maintaining transactionally consistent copies of the primary database, Data Guard, configured with Oracle high availability solutions such as Real Application Clusters (RAC) databases, further enhances the availability and scalability of any given copy of that database. The intrasitehigh availability of a RAC database complements the intersite protection that is provided by Data Guard broker.
Consider that you have a cluster system hosting a primary RAC database comprised of multiple instances sharing access to that database. Further consider that an unplanned failure has occurred. From a Data Guard broker perspective, the primary database remains available as long as at least one instance of the clustered database continues to be available for transporting redo data to the standby databases. Oracle Clusterware manages the availability of instances of a RAC database. Cluster Ready Services (CRS), a subset of code that is a part of Oracle Clusterware, works to rapidly recover failed instances to keep the primary database available. If CRS is unable to recover a failed instance, the broker continues to run automatically with one less instance. If the last instance of the primary database fails, the broker provides a way to fail over to a specified standby database.
The broker is integrated with CRS so that database role changes occur smoothly and seamlessly. This is especially apparent in the case of a planned role switchover (for example, when a physical standby database is directed to take over the primary role while the former primary database assumes the role of standby). The broker and CRS work together to temporarily suspend service availability on the primary database, accomplish the actual role change for both databases during which CRS works with the broker to properly restart the instances as necessary, then to resume service availability on the new primary database. The broker manages the underlying Data Guard configuration and its database roles while CRS manages service availability that depends upon those roles. Applications that rely on CRS for managing service availability will see only a temporary suspension of service as the role change occurs in the Data Guard configuration.
Note that, while CRS enhances availability of a given copy of the RAC database, the broker enhances availability of the sites and databases across multiple geographically dispersed locations, hence providing disaster protection. Together, the broker and Oracle Clusterware provide a strong foundation for Oracle's high-availability architecture.
Data Guard Broker Management Model
The broker simplifies the management of a Data Guard environment by performing operations on the following logical objects:
The broker supports one or more Data Guard configurations, each of which includes a profile for the primary database and each standby database. A supported broker configuration consists of:
· A configuration object, which is a named collection of database profiles. A database profile is a description of a database object including its current state, current status, and properties. The configuration object profiles one primary database and its standby databases that can include a mix of both physical and logical standby databases. The databases of a given configuration are typically distributed across multiple host systems.
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