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Oracle9i Data Guard Broker Concepts

This chapter describes the Oracle9i Data Guard broker, its architecture and components, and how it automates and simplifies the creation, control, and monitoring of a Data Guard configuration. The assumption is that you already have an understanding of Oracle9i Data Guard terminology and concepts.

The following sections introduce Data Guard broker terminology and concepts:

• Section 1.1, "Oracle9i Data Guard Broker Overview"
• Section 1.2, "Benefits of Data Guard Broker"
• Section 1.3, "Data Guard Broker Management Model"
• Section 1.4, "Data Guard Broker Components"
• Section 1.5, "Data Guard Broker User Interfaces"
• Section 1.6, "Data Guard Monitor"
• Section 1.7, "Oracle9i Data Guard Installation, Upgrade, and First Use"

  
  

  See Also: Oracle9i Data Guard Concepts and Administration for complete information about Oracle9i Data Guard concepts and terminology

1.1 Oracle9i Data Guard Broker Overview

The Oracle9i 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 that the broker automates and simplifies:

• Creating and enabling one or more Data Guard configurations, with each configuration incorporating a primary site and database, a new or existing standby site and (physical or logical) standby database, and configuring log transport services, and log apply services
• Adding up to 8 additional new or existing sites and (physical or logical) databases to each existing Data Guard configuration, for a total of one primary site and database, and from 1 to 9 standby sites and databases in the same configuration
• Managing an entire Data Guard configuration from any site in the configuration, including all sites and databases, log transport services, and log apply services
• Invoking switchover or failover operations with a single command to initiate and control complex role changes across all systems in the configuration
• Monitoring log apply rates, capturing diagnostic information, 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: Oracle9i Data Guard Manager, which is the broker's graphical user interface (GUI) and the Data Guard command-line interface (CLI).

1.2 Benefits of Data Guard Broker

The broker's easy-to-use interfaces improve usability and centralize management and monitoring of the Data Guard configuration, resulting in the following benefits:

Enhanced high availability and disaster protection:

By automating the tasks required to configure and monitor a Data Guard configuration, the broker enhances the high availability and disaster protection capabilities that are inherent in Oracle9i Data Guard. Access is possible through any client on any system in the Data Guard configuration, eliminating any single point of failure. If the primary system fails, any of the standby databases can be used for production processing.

Automated creation of a Data Guard configuration:

The broker helps you to logically define and create a Data Guard configuration consisting of a primary site and a local or remote (physical or logical) standby site. If you use Data Guard Manager, it also automatically configures the communication between the sites and databases in a Data Guard configuration, which can be connected by a LAN and Oracle Network Services in the same data center, or--for maximum data protection--geographically dispersed over a WAN and connected by Oracle Network Services.

Data Guard Manager provides a wizard that automates the complex tasks involved in creating a broker configuration, including adding a new or existing standby database, and configuration of the standby control file, initialization parameter file, and datafiles. Although the CLI interface cannot automatically create a new standby database, the CLI can configure and monitor an existing standby database.

Easy configuration of additional standby databases:

After you create a Data Guard configuration consisting of a primary and standby database, you can add up to eight new or existing, physical or logical standby databases to each Data Guard configuration. Data Guard Manager provides an Add Site wizard to guide you through the process of adding more sites and database resources. Data Guard Manager also makes all Oracle Net configuration changes necessary to support log transport services and log apply services across all sites in the configuration.

Simplified, centralized, and extended management:

You can issue management commands from any system in the configuration to:

• Coordinate resource state transitions and modify resource properties while ensuring that changes are made to all of the sites in the configuration.
• Manage all components of the configuration, including the primary and standby sites and databases, log transport services, and log apply services.
• Update database properties dynamically with the broker recording the changes in a Data Guard configuration file that contains information about all of the objects in the configuration, and propagating the changes to the related databases and their SPFILEs in the Data Guard configuration.
• Dynamically tune the configuration protection modes (to maximize protection, to maximize availability, or to maximize performance) and balance the level of data protection against the impact on application performance.
• Use verify commands to ensure that log transport services and log apply services are configured and functioning properly.

Automated switchover and failover operations:

Only one command is required to initiate complex role changes for switchover or failover operations across all systems in the configuration. Data Guard Manager provides switchover and failover wizards that automate switchover and failover to a specified standby site in the broker configuration. Data Guard Manager prompts you to choose a new primary site from a list of viable standby sites (enabled and online, with normal status). The CLI SWITCHOVER and FAILOVER commands require you to specify only the target standby site before automatically initiating and completing the many steps in switchover or failover operations across the multiple sites in the configuration.

Built-in monitoring and alert and control mechanisms:

The broker provides built-in validation that monitors the health of all of the sites in the configuration. From any system in the configuration, you can capture diagnostic information and detect obvious and subtle problems quickly with centralized monitoring, testing, and performance tools. Both Data Guard Manager and the CLI retrieve a complete configuration view of the primary log transport queue depth and the standby log apply queue depth, in addition to data specific to physical and logical standby databases.

Also, the ability to monitor local and remote databases and respond to events is significantly enhanced by the broker's health check mechanism and Data Guard Manager's interaction with the Oracle Enterprise Manager event management system.

Transparent application integration:

Use of the broker is possible for any database because the broker works transparently with applications; no application code changes are required to accommodate a configuration that you manage with the broker. However, you will need to reconnect applications after a failover or switchover occurs.

1.3 Data Guard Broker Management Model

The broker simplifies the management of a Data Guard environment by performing operations against three logical objects:

• Configuration
• Site
• Database resource

The broker supports one or more Data Guard configurations, each of which contains one primary site and database, and from one to nine physical or logical standby sites and databases. A supported broker configuration consists of:

• A configuration object, which is a named collection of sites and the resource objects that those sites contain. The configuration object contains one primary site object and up to nine standby site objects that can include a mix of both physical and logical standby databases. The site objects contained in a given configuration are typically distributed across multiple host systems.
• Site objects are named collections of resource objects with each site typically residing on a single host. The primary site object contains a database resource object that represents a primary database, and each standby site object contains a database resource object that represents either a physical or a logical standby database.
• Database resource objects, which are named objects, correspond to primary or standby database instances. The broker uses each database resource object to manage and control the state of a single database on a given site.

Figure 1-1 shows the hierarchy of these objects.

Figure 1-1 Hierarchy of Objects Managed by the Data Guard Broker

Text description of the illustration mgtmodel.gif

Because these objects are connected in a hierarchy, you can perform complex operations on a single object or on all objects in an entire configuration with a single mouse click or command. For example, you can bring each database resource and site in a configuration online one at a time, or bring them all online at the same time in a single step by bringing the configuration itself online.

1.4 Data Guard Broker Components

The Oracle9i Data Guard broker consists of the following components:

• Oracle9i Data Guard Manager
• Data Guard Command-Line Interface (DGMGRL)
• Data Guard Monitor

The Data Guard Manager graphical user interface and the Data Guard command-line interface are the broker client-side components that help you define a configuration consisting of a collection of primary and standby database sites. Section 1.5 describes these interfaces in more detail.

The Data Guard monitor is the broker server-side component that is integrated with the Oracle database server. Data Guard monitor is composed of the DMON process and Data Guard configuration files that allow you to control the objects of that configuration, modify object behavior at runtime, monitor the overall health of the configuration, and provide notification of other operational characteristics. Section 1.6 describes the Data Guard monitor in more detail.

Figure 1-2 shows these components of the broker.

Figure 1-2 Components of Oracle9i Data Guard Broker

Text description of the illustration odg.gif

1.5 Data Guard Broker User Interfaces

You can use either of the broker's user interfaces to create a broker configuration and to control and monitor the configuration from any host in the configuration. The following sections describe the broker's user interfaces:

• Oracle9i Data Guard Manager
• Data Guard Command-Line Interface (DGMGRL)

1.5.1 Oracle9i Data Guard Manager

The Data Guard Manager is a graphical user interface that works with the Data Guard monitor and Oracle Enterprise Manager to automate and simplify the management of a Data Guard configuration. Because it is integrated with Oracle Enterprise Manager, Data Guard Manager allows you to manage your configuration using a familiar interface and event management system.

With Data Guard Manager, the complex operations of creating and managing standby databases are simplified through wizards provided by Data Guard Manager. Data Guard Manager includes:

• A Create Configuration wizard that helps you to create a broker configuration having a primary site and a local or remote standby site. The wizard can create the standby site and either create its physical or logical standby database, or import an existing physical or logical standby database. If creating the physical or logical standby database, it also automates the creation of the standby control file, the standby initialization parameter file and SPFILE, log files, and the standby datafiles.
• An Add Site wizard that creates and adds new standby sites, and either creates its physical or logical standby database or imports an existing physical or logical standby database. or imports existing standby sites, into an existing broker configuration.
• A Switchover wizard that guides you through the steps to switch roles between the primary site and a standby site.
• A Failover wizard that changes one of the standby sites and its database into the role of a primary site and database.
• Performance tools and graphs that help you monitor and tune log transport services and log apply services.
• Property pages that allow you to set database properties on any site or database and, if applicable, the settings are immediately replicated to all other sites, databases, and server parameter files (SPFILE) in the configuration.
• Integration with Oracle Enterprise Manager to perform proactive event reporting through e-mail or pagers.

In addition, it makes all Oracle Net configuration changes necessary to support log transport services and log apply services

Figure 1-3 shows the general page from the Oracle9i Data Guard Manager main window.

Figure 1-3 Oracle9i Data Guard Manager Main Window

Text description of the illustration genconfig.gif

1.5.2 Data Guard Command-Line Interface (DGMGRL)

The Data Guard command-line interface (CLI) allows you to control and monitor a Data Guard configuration from the CLI prompt or within scripts. You can perform most of the activities required to manage and monitor the objects in the configuration using the CLI.

The following example lists the available commands:

DGMGRL> HELP
The following commands are available:
quit
exit
show                See "help show" for syntax
enable              See "help enable" for syntax
disable             See "help disable" for syntax
help                 [<command>]
connect             <user>/<password> [@<connect>]
alter               See "help alter" for syntax
create              See "help create" for syntax
remove              See "help remove" for syntax
failover
shutdown
startup
switchover

This guide provides examples and reference information for the Data Guard command-line interface.

1.6 Data Guard Monitor

The configuration, control, and monitoring functions of the broker are implemented by server-side software and configuration files that are maintained on each site that the broker manages. The software is called the Data Guard monitor.

The following sections describe how the Data Guard monitor interacts with the Oracle server and with remote Data Guard monitors to manage the sites in a broker configuration.

1.6.1 Data Guard Monitor (DMON) Process

The Data Guard monitor process (DMON) is an Oracle background process that runs on every site that is managed by the broker. When you start the Data Guard monitor, a DMON process is created.

When you use Data Guard Manager or the CLI to manage an object, the DMON process is the server-side component that interacts with the local instance and the DMON processes running on other sites to perform the requested function. The DMON process is also responsible for monitoring the health of the broker configuration and for ensuring that every site has a consistent copy of the binary configuration files in which the DMON process stores its configuration data.

Figure 1-4 shows the DMON process among several background processes that perform maintenance work for the Oracle database server.

Figure 1-4 Oracle9i Broker Background Process

Text description of the illustration dmon.gif

The zigzag arrow in the center of Figure 1-4 represents the two-way Oracle Net communication channel that exists between the DMON processes on sites in the same broker configuration.

This two-way communication channel is used to pass requests between sites, and to monitor the health of all of the sites in the broker configuration.

1.6.2 Configuration Management

The broker's DMON process maintains persistent configuration data about all objects in the broker configuration in a binary configuration file. A copy of this file is maintained by the DMON process on each of the sites that belong to the broker configuration. Changes to this file are made by the DMON process for all copies.

This configuration file contains entries that describe the states and properties of the objects in the configuration. For example, the file records the sites and databases that are part of the configuration, the roles and properties of each of the databases, and the state of each of the objects of the configuration.

The configuration data is managed transparently by the DMON process to ensure that the configuration information is kept consistent across all of the sites. The broker uses the data in the configuration file to configure and start the site and database resource objects, control each object's behavior, and provide information to the CLI and Data Guard Manager. (See Section 4.3.2 for more information.)

Whenever you add site or database resource objects to a broker configuration, or make a change to an existing object's properties, each DMON process records the new information in its copy of the configuration file.

Two copies of the file are maintained per site so as to always have a record of the last known valid state of the configuration. When the database instance is started, the configuration files are named automatically using a default name that is operating-system specific. You can override this default name on any given site by setting the following initialization parameters for that site:

DG_BROKER_CONFIG_FILE1
DG_BROKER_CONFIG_FILE2

You can also change the configuration file names dynamically by issuing the ALTER SYSTEM SQL statement. However, you cannot alter these parameters when the DMON process is running. To change the names of these configuration files on a given site, perform the following steps:

1. Disable the broker configuration using the CLI DISABLE command or the Disable operation in Data Guard Manager. See Section 2.4.
2. Stop the Data Guard broker DMON process using the following SQL statement:

   SQL> ALTER SYSTEM SET DG_BROKER_START=FALSE;
   
   

3. Change the configuration file names on the site:

   SQL> ALTER SYSTEM SET DG_BROKER_CONFIG_FILE1=filespec1
   SQL> ALTER SYSTEM SET DG_BROKER_CONFIG_FILE2=filespec2
   
   

4. Rename the existing files to filespec1 and filespec2, respectively, at the operating system level to avoid losing the existing broker configuration information.
5. Restart the Data Guard broker DMON process on the site, as follows:

   SQL> ALTER SYSTEM SET DG_BROKER_START=TRUE;
   
   

6. Enable the broker configuration using the CLI ENABLE command or the Enable operation in Data Guard Manager.

1.6.3 Database Property Management

Associated with each site and database resource object are various properties that the DMON process uses to control the object's behavior. The properties are recorded in the configuration file as a part of the object's definition that is stored there. In particular, many database resource properties are used to control database initialization parameters related to the Data Guard environment.

To ensure that the broker can update the values of parameters in both the database instance itself and in the configuration file, you must use a persistent server initialization parameter file (SPFILE) to control static and dynamic initialization parameters. The use of a SPFILE gives the broker a mechanism that allows it to reconcile property values selected by the DBA when using the broker with any related initialization parameter values recorded in the SPFILE.

Thus, when you set definitions or values for database properties in the broker configuration, the broker records the change in the configuration file and also propagates the changes to all of the sites in the Data Guard configuration.

1.7 Oracle9i Data Guard Installation, Upgrade, and First Use

Oracle9i Data Guard and the broker (including the CLI) are included with the Enterprise Edition or Personal Edition of the Oracle9i database server software.

The Oracle9i Data Guard Manager graphical user interface is included with the Oracle Enterprise Manager software.

1.7.1 Installation

To use the broker and the CLI, you must install the Oracle9i Enterprise Edition or Personal Edition database server on each site where you plan to manage broker configurations.

If you plan to use the Oracle9i Data Guard Manager graphical user interface to manage broker configurations, you must install it with the Oracle Enterprise Manager software.

1.7.2 Upgrade

If you are currently running an Oracle9i Data Guard Release 1 (9.0.1) configuration, you must upgrade to Oracle9i Release 2 (9.2) and recreate the broker configuration, as follows:

1. Delete the release 9.0.1 broker configuration using the Data Guard Manager or the CLI release 1 (9.0.1).
2. Upgrade the database server software to Oracle9iRelease 2 (9.2). See the Oracle installation documentation that is appropriate for your operating system.
3. If you are using Oracle9i Enterprise Manager and Data Guard Manager Release 1 (9.0.1), you must upgrade to Oracle9i Enterprise Manager Release 2 (9.2) to manage a broker configuration running Oracle9i Data Guard Release 2 (9.2):
   • Data Guard Manager Release 1 (9.0.1) is not compatible with Oracle Data Guard Release 2 (9.2).
   • Data Guard Manager Release 2 (9.2) is not compatible with Oracle Data Guard Release 1 (9.0.1). You will receive an error message stating that the Oracle database is too old.
4. If you are using the CLI Release 1 (9.0.1), you must upgrade to Data Guard command-line interface Release 2 (9.2):
   • The CLI Release 1 (9.0.1) is not compatible with Oracle Data Guard Release 2 (9.2).
   • The CLI Release 2 (9.2) is not compatible with Oracle Data Guard Release 1 (9.0.1).
5. Invoke Data Guard Manager or the CLI and re-create the broker configuration.

   See Also: Oracle9i Database Migration if you are upgrading from Oracle8i Data Guard to Oracle9i Data Guard

1.7.3 Prerequisites for First Use

The following conditions must be true before you can use the broker:

• The primary and standby databases must be running Oracle9i release 2 and installed in a single-instance environment (not an Oracle Real Applications Clusters environment). The database server must be licensed for Oracle9i Enterprise Edition or Personal Edition.
• You must use a persistent server initialization parameter file (SPFILE) to ensure the broker can persistently reconcile values between broker properties and any related initialization parameter values. See Section 1.6.3 for more information.
• The value of the DG_BROKER_START parameter must be set to TRUE. See Section 2.2 for more information. (Data Guard Manager sets this parameter for you automatically.)
• You may need to set up the DG_BROKER_CONFIG_FILEn initialization parameter. See Section 1.6.2 for more information.
• Oracle Net network files must be set up on the primary database site and on the the standby database site if you configure an existing standby database into the broker configuration. Otherwise, Data Guard Manager automatically sets up the network files when it creates a standby database.
• The primary instance must be opened in archivelog mode. (Data Guard Manager does this for you automatically.) If there is an existing standby instance, it must be mounted.
• You must also set the COMPATIBLE initialization parameter to 9.0.0.0.0 or higher for both the primary and standby databases.
• If you plan to configure an existing standby database into the broker configuration, you must set up a remote login password file to enable management of a remote standby database. Data Guard Manager automatically sets up the remote password file when it creates a standby database.

  See Also: Section 2.2 for more information about preparing and starting Oracle9i Data Guard. See Oracle9i Data Guard Concepts and Administration for more information about setting up the network files.