Data Guard Broker Tips Oracle Tips by Burleson Consulting December 3, 2011

Data Guard Broker Architecture

Data Guard Broker is an assistance utility that is provided with Oracle Database Server software to facilitate the creation and management of Data Guard configurations. Data Guard Broker consists of server side and client side components that are used together in the implementation of a distributed computing architecture.

The server side component includes a Data Guard Monitor (DMON) process and configuration files. The client side component includes Data Guard Manager and a Command Line interface.

Data Guard Broker manages a Data Guard configuration using a broker management model. The broker management model is a hierarchal structure comprised of Configuration, Site and Database resources. Broker can manage all three layers of the management model. More information about the broker management model will be presented later in this section.

Data Guard Broker is available with Oracle 9i Release 2 or above.

Data Guard Broker Architecture

Data Guard Broker can manage the primary database and up to nine standby databases in one configuration. These nine standby databases can be a mixture of physical and logical standby databases. Standby databases can be created using Data Guard broker.  In addition, it can be used to add an existing Data Guard primary database to a configuration. 

When a Oracle instance is created using Broker, Broker takes care of the entire set of supporting files such as SPFILE, Oracle Net configuration files, etc.  If a DBA needs to add an existing Oracle instance to a Data Guard configuration, the SPFILE and Oracle Net files must be configured manually before the Data Guard primary database  is added to a configuration.  If Data Guard Broker is to be used for the management of standby databases, SPFILE must be used to hold the initialization parameters on all the participating databases.

Some advantages of using Data Guard Broker are as follows:

• It is a centralized management tool that can be used to manage the entire configuration using a GUI or CLI interface.
   

• It provides an extensive health check mechanism for the primary database, standby databases and supporting services in the configuration.
   

• It reduces the complexity of role management services. Switchover and Failover operations can be performed from a centralized console.
   

• It can be used to gather useful statistics for fine tuning the log transfer and log apply services.

In Oracle 9i and beyond, Data Guard Broker cannot be used with Oracle Real Application Cluster. RAC support is provided with Oracle 10g and beyond.

The following subsections will present the broker management model and the broker components, in brief.

Data Guard Broker Configuration, Data Guard Broker Sites and Data Guard Broker Resources

The Broker management model is a three layer hierarchical framework. The logical units of the management model are Configuration, Site and Database Resources. These three layers share a parent-child relationship as shown in Figure 2-3 below.

Figure 2.3 – The relation between layers of the Broker management model.

A Database Resource is the smallest unit managed by Data Guard Broker.  In the Broker management model, a database resource represents an instance of the primary or standby database. In addition, a service such as the log apply service can be classified as a database resource in the context of a management model. The site in this model is a collection of database resources.

In other words, a site is equivalent to a host machine on which a database instance is running. Configuration is the largest unit in the Broker management model and consists of the primary site and one or more standby sites.

Data Guard Broker can manage all three layers of the management model. Any operation performed on a higher level of the model is applicable to all child objects of that layer. For example, if the status of a site is changed to offline, all the resources under that site will be offline.