Enhanced RMAN Integration with Data Guard - Oracle 11g

Oracle Database 11g provides better integration between RMAN and Data Guard.The following are the main enhancements in the Data Guard/RMAN area.

Configuring RMAN Without a Database Connection

You can now connect to any database in a Data Guard setup and make persistent RMAN configuration changes for any other standby site in the Data Guard configuration.That is, you don’t have to connect to the particular database you’re making RMAN configuration changes to, unlike in the previous releases.

The new for db_unique_name clause, which you can use with the configure, show,list,and report schema commands,makes it possible for you to view and make changes to the persistent RMAN configuration for a database without connecting to that database using the keyword target.Most of the RC_* views, such as the RC_DATAFILE and RC_RMAN_OUTPUT views, now contain a new column named DB_UNIQUE_NAME that relates a specific row to a standby site.

Viewing Configuration Information

You can view configuration information configuration by using the db_unique_name option of the show command. You must be connected to a recovery catalog and any target database that is mounted or open in order to use the for db_unique_name clause.You can also use this option after executing the set dbid command. Here’s an example showing how to use the for db_unique_name option:

RMAN> show for db_unique_name <site_name>;

The previous command will show the persistent RMAN configuration settings for the site you specify with the site_name clause.You can similarly use the for db_unique_name option as part of the list, report,and show schema commands, as shown here:

The for db_unique_name clause isn’t applicable to just a single site. You can use any of the commands listed in this section—show, list, report, and report schema with the for db_unique_name option and the all clause—to view the configuration or other information for all sites.

That is, you just replace the site_name clause with the all clause to make the command apply to all sites.For example,to view the current persistent configuration settings set for all sites in your Data Guard configuration, issue the following command:

RMAN> show for db_unique_name all;

You can use the list,report, and report schema commands in the same way.

Making Configuration Changes for a Site

Use the for db_unique_name clause of RMAN’s configure command to make persistent configuration changes to a specific standby site, without actually connecting to it.The for db_unique_name clause leads RMAN to automatically connect to the specified standby site and update its controlfile with the new configuration changes.

If you use the for db_unique_name clause with the all option instead of the site_name option, RMAN will connect to all databases registered in the recovery catalog and will update their control files with the new settings.

Renaming a Standby Site

You can rename a standby site in the recovery catalog by using the change
db_unique_name command,as shown here:

The previous command will associate the RMAN metadata for the old db_unique_name to the new db_unique_name you provided.

Removing a Standby Site

You can remove information about a specific standby site from the recovery catalog with the help of an enhanced unregister command,wherein you can use the db_unique_name clause to specify a particular standby site name.You must be connected,of course, to the recovery catalog and any mounted target database when you issue the command,which has the following syntax:

RMAN> unregister db_unique_name site_name;

If you want to get rid of the actual backups for a standby site, add the including backups clause to the previous command.This command is applicable to both primary and standby databases.

Restoring a Backup Controlfile to a Standby Controlfile

In Oracle Database 11g, you don’t need to back up a standby controlfile on the primary database when creating a standby database.You also don’t need to create a backup controlfile on all your standby sites.RMAN performs an automatic reverse synchronization of the necessary data to all the (physical) standby databases.

Use the new restore controlfile command to restore a backup controlfile to a standby controlfile and to restore the controlfile for the primary database from the standby controlfile backups as well.There are three variations of the restore controlfile command, as shown here:

During the restore of the controlfile,RMAN performs the actions so the controlfile is converted to a standby controlfile the first time that control file is mounted.

Resynchronizing the Recovery Catalog

You can resynchronize the RMAN recovery catalog from a remote database using an enhanced reysnc catalog command,which does the resynchronization when you add the new db_unique_name option.

Before you use the resync catalog command to perform the recovery catalog resynchronization, however, you must first define the connect identifiers for the standby databases in your Data Guard configuration by using the configure command with the new clause connect identifier.

Here’s how you define a connect identifier for a specific standby site in your Data Guard configuration:

You must enclose the connect identifier name you supply in quotes.The database you are connected to through RMAN will connect automatically to the remote standby site using the connect identifier you create, as the privileged user sys.

Although RMAN can use the connect identifier to process information back and forth with the remote standby site,in this chapter,our interest is in using the connect identifier as part of the resync catalog command.You can use the resync catalog command to resynchronize the catalog with a specific standby site’s information (by using the site_name clause),or if you have configured connect identifiers for all databases in your Data Guard configuration, use the all clause in the resync catalog command. Here’s an example:

Oracle recommends you define the connect identifier for all databases in your Data Guard configuration.

Backup File Accessibility Groups

In Oracle Database 11g,all backup,restore,and recover commands auto matically figure out the correct file names for each of the standby sites in the Data Guard configuration.This transparency is extremely useful when you’re dealing with databases that contain a large number of datafiles or use an automatic storage management (ASM) file system or an Oracle Managed Files (OMF) file system, where the file names tend to be unwieldy.

You can create a group of sites that can share backups for a device type by using the new configure group command to create a group of standby sites, formally known as a backup file accessibility group. A standby site can belong to multiple groups. Here’s how you create a new group of standby sites:

Make sure you connect to the recovery catalog before executing the command shown here.The target database you’re connected to can be mounted or open.The previous command creates a backup file accessibility group with three standby sites, whose backups are accessibleby each of the three sites. Besides providing the ability to share backups among the group members, RMAN also lets the restore and recover commands use the backup file accessibility groups during file restoration from backups.

Block Change Tracking Support in Standby Databases

RMAN has provided a block change tracking feature in earlier releases of the Oracle database.The block change tracking feature improves backup performance considerably by backing up only the changed data blocks during incremental backups.Block change tracking is recommended because it avoids having to scan entire datafiles for changed data when the database may be undergoing modifications in only a small percentage of the data blocks in the database.

In Oracle Database 11g, for the first time, you can set up block change tracking in a standby data base.Please see Chapter 10 for an explanation of the block change tracking in a Data Guard environment.


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