Data Guard Broker - Basics

DG BROKER is the management framework for data guard, and allows the DBA’s to automate many of the tasks involved in configuring and monitoring an Oracle Data Guard configuration.

DG Broker provides two interfaces:

1.       DGMGRL utility – this is a command line interface to the DG Broker

2.       OEM  GUI – OEM provides a graphical interface to the DG Broker

Some features such as standby database creation, can be automated and are only available through the GUI interface. If you use the DGMGRL utility and want to create a standby atabase, you must do so manually.

Benefits of DG Broker:

·         Disaster protection

·         High availability and scalability with RAC

·         Automated creation of DG configuration

·         Easy creation of additional standby DB’s (through OEM)

·         Simplified and centralized management

·         Simplified switchover and failover

·         Transparent to applications

DG broker handles the following logical entities:

·         Configuration of databases

A DG Broker configuration consists of following entities:

-          Configuration Object: it is a named collection of database profiles. A database profile in turn is a description of a database object including its current state, status and properties. A configuration object profiles one primary database and its standby databases.

-          Database objects: these correspond to the primary and standby databases. Broker uses the database object’s profile to manage and control the state of a single database on the system.

-          Instance objects: Broker treats databases as a collection of one or more named instances. Broker automatically discovers instances and associates them with their databases.

·         A single database

Data Guard Monitor and DG Configuration files

   The configuration, control and monitoring functions of the Broker are implemented by server-side software and configuration files.

This software is known as Data Guard Monitor.

When the Broker is started, the DMON (data guard monitor) background process runs for every database instance that is managed by the broker. DMON process interacts with the local instance and the DMON processes of all other instances in the broker configuration to perform the requested operation. It is also responsible for monitoring the health of broker configuration and for ensuring that every database has a consistent description of the configuration.

This persistent description of configuration is stored in the binary configuration file. A copy of this file is maintained by the DMON process for each database that belongs to the broker configuration. Configuration file describes the states and properties of the databases in configuration.  

Using SPFile is a must when using DG Broker to ensure that the Broker can update the values of parameters in both the database (parameter file) and the configuration file.

Broker Processes

DMON – Data Guard Monitor process -                This is the main process, responsible for all broker actions, as well as maintaining the configuration files. This process can be enabled or disabled using DG_BROKER_START parameter.

RSM – Broker Resource Manager – This process is responsible for handling SQL commands used by broker that need to be executed on one of the databases in the configuration. These commands need to be run as a result of change in configuration made through the DGMGRL, or the configuration commands run by broker during database startup.

NSVn – Data Guard Net Services – These processes are responsible for making contact with remote databases and sending across any work items to remote databases.

DRCn – Data Guard Network Receiver –  The network receiver processes establish connection from source database NSVn process. This is similar to the LNS and RFS mechanism for redo transport.