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Oracle® Data Guard Broker
10g Release 2 (10.2)

Part Number B14230-01
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3 Managing Broker Configurations

This chapter contains the following sections:

3.1 Configuration Support

The broker enables you to logically define a Data Guard configuration, consisting of a primary database and one or more standby databases. With the broker, you define a broker configuration that is a logical grouping of the databases, including redo transport services and log apply services. At the DBA's discretion, the broker controls the logical objects in the configuration, modifies their behavior at runtime, monitors the overall health of the configuration, and reports any health and other operational characteristics up through the Oracle Enterprise Management notification mechanisms if you are using Oracle Enterprise Manager, or through SHOW commands if you are using DGMGRL.

The broker supports Data Guard configurations consisting of a primary database, and up to nine standby databases that are either local to, or, remote from, the primary database. Any of those databases can be an Oracle Real Application Clusters (RAC) database.

A supported Data Guard configuration contains the following components:

The Data Guard log apply services update standby databases with redo data that is transmitted automatically from the primary database by redo transport services. The archived redo log files and standby redo log files contain all of the database changes except for unrecoverable or unlogged changes. On physical standby databases, Redo Apply applies the redo data to stay transactionally consistent with the primary database. On logical standby databases, SQL Apply applies the redo data to stay transactionally consistent with the primary database.

The broker's Data Guard monitor (DMON) process configures and maintains the broker configuration as a group of objects that you can manage and monitor as a single unit. Thus, when you enter a command that affects multiple databases, the DMON process:

Through the DMON process, you can configure, monitor, and control the databases and the configuration together as a unit. If you disable the configuration, broker management of all of the databases in the configuration is also disabled. If you later enable the configuration, broker management is enabled for each database in the configuration.

Figure 3-1 shows a two-database broker configuration with the DMON process running at each location and communicating over Oracle Net.

On the primary database, the figure shows the redo transport services in addition to the following main components: the primary database, DMON, the online redo log files, and the archived redo log files. The figure also shows standby redo log files in outline form on the primary side; the standby redo logs are outlined to indicate they are currently inactive but have been configured in preparation for a switchover to the standby role.The standby database includes the following components: a standby database, log apply services, DMON, archived redo log files, and standby redo log files. The online redo log files on the standby database are outlined to indicate they are currently inactive but have been configured in preparation for a switchover to the primary role.


See Also:

Oracle Data Guard Concepts and Administration for more information about physical and logical standby databases

Figure 3-1 Oracle Data Guard Broker Configuration

Description of odg_arch.gif follows
Description of the illustration odg_arch.gif

3.2 Setting Up the Broker Configuration Files

Two copies of the configuration file are maintained for each database so as to always have a record of the last known valid state of the configuration. When the broker is started for the first time, the configuration files are automatically created and named using a default path name and filename that is operating-system specific. You can override this default path name and filename by setting the following initialization parameters for that database:

DG_BROKER_CONFIG_FILE1
DG_BROKER_CONFIG_FILE2

Note the following restrictions when setting the DG_BROKER_CONFIG_FILE1 and DG_BROKER_CONFIG_FILE2 initialization parameters:

The Data Guard Broker works with databases that use either Oracle managed or user managed datafiles. These datafiles can reside on raw devices, a file system or an ASM disk group. The following section contains these topics:

3.2.1 Renaming the Broker Configuration Files

You can change the configuration filenames dynamically by issuing the ALTER SYSTEM SQL statement. However, you cannot alter these parameters when the broker's DMON process is running. To change the names of these configuration files for a given database, perform the following steps:

  1. Disable the broker configuration using the DGMGRL DISABLE command. See Section 3.5.

  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 filenames for the database:

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

    Note:

    If the broker is managing a RAC database, the value of DG_BROKER_CONFIG_FILE1 and the value of DG_BROKER_CONFIG_FILE2 for each of the instances must point to the same set of physical files.

  4. If the configuration files are not located on raw devices, rename the existing files to filespec1 and filespec2, respectively, at the operating system level to avoid losing the existing broker configuration information. If the files are located on raw devices, you must manually move the contents from the old location to the new location.

  5. Restart the Data Guard broker DMON process, as follows:

    SQL> ALTER SYSTEM SET DG_BROKER_START=TRUE;
    
    
  6. Enable the broker configuration using the DGMGRL ENABLE command or the Enable operation in the Data Guard management pages of the Enterprise Manager.

3.2.2 Managing Broker Configuration Files in a Real Application Clusters Environment

If the broker is managing a RAC database, the value of DG_BROKER_CONFIG_FILE1 and the value of DG_BROKER_CONFIG_FILE2 for each of the instances must point to the same set of physical files. In other words, all instances of the database must reference the same set of configuration files. The configuration files can be deployed using one of the following methods:

3.2.2.1 Using Cluster File System (CFS) for Configuration Files

If cluster file system (CFS) is available, and the configuration files reside there, the DG_BROKER_CONFIG_FILEn parameters on all of the instances must be set to these files including the path to the CFS area. Figure 3-2 shows the set up for the broker configuration files on CFS. In this scenario, the parameters and value for all instances would be:

DG_BROKER_CONFIG_FILE1=$ORACLE_BASE/admin/db_unique_name/dr1db_unique_name.dat
DG_BROKER_CONFIG_FILE2=$ORACLE_BASE/admin/db_unique_name/dr2db_unique_name.dat

Figure 3-2 Broker Configuration Setup in a CFS Area

Description of cfs_setup.gif follows
Description of the illustration cfs_setup.gif

3.2.2.2 Using ASM Disk Groups for Configuration Files

The broker's configuration files can also reside on an ASM disk group. Figure 3-3 shows the setup for the broker configuration files on ASM devices. In this scenario, the parameters and values would be specified, as follows:

ALTER SYSTEM SET DG_BROKER_CONFIG_FILE1 = '+DG/DIRECTORY/DR1.DAT' SCOPE=BOTH;
ALTER SYSTEM SET DG_BROKER_CONFIG_FILE2 = '+DG/DIRECTORY/DR2.DAT' SCOPE=BOTH;

Figure 3-3 Broker Configuration Setup with ASM

Description of asm_device_setup.gif follows
Description of the illustration asm_device_setup.gif

Because the configuration files must be explicitly named by the user, these configuration files are not Oracle Managed Files (OMF).To create the broker's configuration files on an ASM disk group, set the DG_BROKER_CONFIG_FILE1 and DG_BROKER_CONFIG_FILE2 initialization parameters to a string value that includes the name of an existing ASM disk group, an existing directory in that disk group, and the name of the configuration file itself.

3.2.2.3 Using Raw Devices for Configuration Files

If CFS is not available and you are not using ASM, the files must be on raw devices. In this case, the parameter values on each of the instances must point to the raw devices. Figure 3-4 shows the set up for the broker configuration files on raw devices. On a UNIX system, you would set this up similar to the following on each node:

%ln -s /dev/rdsk/c1t2d3s5 dr1/<db_unique_name>.dat
%ln -s /dev/rdsk/c1t2d3s6 dr2/<db_unique_name>.dat

Figure 3-4 Broker Configuration Setup with Raw Devices

Description of raw_device_setup.gif follows
Description of the illustration raw_device_setup.gif

If the broker configuration files need to be on raw devices, set up two additional raw devices of 1MB each. Set up the value of the DG_BROKER_CONFIG_FILE1 and DG_BROKER_CONFIG_FILE2 parameters to point to the raw devices. A 1MB configuration file will accommodate 10 databases with a total of 45 instances between them.

You may need a larger device if the number of instances for this configuration exceeds 45 instances. You will need 15KB for each additional instance.

3.3 Starting the Data Guard Broker

After setting up the configuration files, the DG_BROKER_START initialization parameter must be set to TRUE for each database to start the DMON processes.

By default, the DG_BROKER_START initialization parameter is set to FALSE. However, you can set the value in the following ways:

Whether you use Enterprise Manager or DGMGRL, set the value of the DG_BROKER_START initialization parameter to TRUE in the server parameter file on each primary and standby database. Doing so ensures that the DMON processes will start automatically the next time you start any instance of the database.

3.4 Management Cycle of a Broker Configuration

The broker helps you to create a new configuration or manage an existing configuration. Figure 3-5 shows the life cycle of a broker configuration.

Figure 3-5 Life Cycle of a Broker Configuration and Its Databases

Description of lifecycl.gif follows
Description of the illustration lifecycl.gif

Create the Broker Configuration

When using Enterprise Manager, the Add Standby Database wizard can either add an existing (RAC or non-RAC) standby database into the configuration or create a new (non-RAC only) standby database and add it to the configuration. The standby database can be either a physical or logical database.

When using DGMGRL, the primary database and a standby database must already exist. You construct the standby database from backups of the primary database control files and datafiles, and then prepare it for recovery.


See Also:

Chapter 6 and Chapter 7 that describe the preparation requirements if you are using Enterprise Manager or DGMGRL, respectively

Enable the Broker Configuration

A Data Guard configuration must be enabled to be managed or monitored by the broker. Conversely, you disable a configuration if you no longer want to manage it with the broker. When you disable a configuration, broker management of all of its databases is also disabled.


Note:

You can enable or disable the configuration using DGMGRL. You cannot disable the configuration using Enterprise Manager. You can enable the configuration using Enterprise Manager in the event that it was previously disabled using DGMGRL.

A broker configuration, when first created using Enterprise Manager, is automatically enabled as soon as the Add Standby Database wizard completes.

A broker configuration, when first created using DGMGRL, is in a disabled condition. This means its constituent databases are not yet under active control of the broker. When you finish configuring the databases into a broker configuration with DGMGRL, you must enable the configuration to allow the broker to manage the configuration.

You can enable:

You can easily disable a database if a problem occurs and you can no longer function properly in the broker configuration.

You may also want to disable a configuration temporarily, and then change some properties in the broker configuration without affecting the actual database properties. The changed properties will take effect when the configuration is enabled again for management by the broker.

Make Role Changes Within the Broker Configuration, As Needed

At any time, you can issue a single command to change the roles of the databases in the configuration. If some event renders the primary database unusable, you can fail over one of the standby databases to become the new primary database.

In addition, planned downtime for maintenance can be reduced because you can quickly switch over production processing from the current primary database to a standby database, and then switch back again after the planned maintenance.


See Also:

Chapter 5 for more information about role changes

Make State Changes to the Databases, As Needed

The broker transitions the databases into an online state, by default, the first time that you enable the database.

At any time, you can issue a single command through Enterprise Manager or DGMGRL to change the state of the database. For example, you could bring the primary database into a LOG-TRANSPORT-OFF state to temporarily stop archiving log files to the standby database. Then, you issue another command to return the database to a full online state (that is, online and archiving log files to the standby databases).


See Also:

Chapter 4 for more information about database state changes

Update Database Properties, As Needed

The broker enables you to set database properties, some of which correspond to database initialization parameters. You can change these properties to dynamically control such things as redo transport, file management, log apply, and to support the overall configuration protection mode. The broker records the changes in the broker configuration file for each database in the Data Guard configuration and propagates the changes to the related initialization parameters in the server parameter files, if needed.


See Also:

Chapter 4 and Chapter 9 for complete information about database properties

Set Data Protection Levels, As Needed

The broker enables you to set the data protection level for the configuration. You can configure the protection mode to maximize data protection, maximize availability, or maximize performance.


See Also:

Section 4.6 for information about managing data protection modes

Monitor the Configuration

You can check the health of the configuration, display and update the properties of the databases, and set Oracle Enterprise Manager events.

Enterprise Manager also provides a dynamic performance page that automatically and dynamically refreshes chart data and status at specified intervals. The performance chart shows a graphical summary of how far behind and how much redo data is being generated and applied.


See Also:

Chapter 6 and Chapter 7 for scenarios that show examples using Enterprise Manager and DGMGRL, respectively

3.5 Enable and Disable Operations

A key concept of management with the broker is the notion of enabling and disabling broker management of the databases in a broker configuration. The enable and disable operations are defined for databases that were incorporated into a broker configuration; you cannot perform these broker operations on databases that are not part of the broker configuration. This is because when you enable or disable a database in the broker configuration, you are effectively enabling or disabling the ability of the DMON process to:

However, disabling a broker configuration does not affect current services and operations in the actual Data Guard configuration. For example, when you disable a broker configuration, redo transport services and log apply services in the Data Guard configuration continue to function unchanged, but you can no longer manage them through the broker interfaces.

In addition, disabling a database does not remove or delete its profile from the broker configuration file. You can reenable your ability to manage with the broker using the DGMGRL ENABLE CONFIGURATION or ENABLE DATABASE commands, or the Enable option in the Data Guard management pages of Enterprise Manager.


Note:

You can enable or disable the configuration using DGMGRL. You cannot disable the configuration using Enterprise Manager. You can enable the configuration using the Enterprise Manager in the event that it was previously disabled using DGMGRL.


Caution:

If you disable broker management of a standby database in the broker configuration, that standby database cannot be used by the broker as a failover target in the event of loss of the primary database.

Disabling broker management of the configuration may be useful to do even though you are removing the broker's ability to monitor and control the databases. For example, it may be advantageous to disable a configuration temporarily in order to change one or more properties in the broker configuration all at the same time. When you change properties in a disabled configuration, it does not affect the actual database properties underneath because the changes are not applied to the running database until you reenable the configuration. For example, you might want to change the overall configuration protection mode and the redo transport services properties on a disabled configuration so that all changes are applied to the configuration at the same time upon the next enable operation.


Note:

For Oracle9i, the configuration object is in either an online or offline state. For Oracle Database 10g, the configuration object is always in an online state.

3.6 Configuration Status

A configuration status reveals the overall health of the configuration. Status of the configuration is acquired from the status of all of its databases.

The following list describes the possible status modes for a configuration: