Databases Reference
In-Depth Information
How It Works
Using a recovery catalog makes it straightforward to restore the control file. When you issue the
restore controlfile
command, RMAN will retrieve from the recovery catalog the location and name of the file that contains the control
file backup and restores the control file appropriately. Because the recovery catalog knows the location of the RMAN
backup piece, it doesn't matter whether the backup piece is in a fast recovery area, or in a configured channel
location, or if you're using the auto backup of the control file feature.
When you're connected to the recovery catalog, you can view backup information about your control files even
while your target database is in nomount mode. To list backups of your control files, use the
list
command as shown
here:
RMAN> connect target /
RMAN> connect catalog rcat/rcat@rcat
RMAN> startup nomount;
RMAN> list backup of controlfile;
Keep in mind the prior command isn't possible if you're not using a recovery catalog. When not using the
recovery catalog, the RMAN backup information is stored in the control file. And if you've lost all your control files,
you won't be able to place your database in mount mode until you've restored a control file.
If you have registered two databases in the recovery catalog with the same name, then you might receive an error
such as this when you attempt to list backups or restore the control file:
RMAN-06004: ORACLE error from recovery catalog database:
RMAN-20005: target database name is ambiguous
In this situation, you will need to first set your database identifier (DBID) before you can restore your control file.
This is because the database name stored in the recovery catalog is not guaranteed to be unique. You can determine
the DBID and verify that you have multiple databases with the same name in your recovery catalog by querying the
recovery catalog database RC_DATABASE view as shown here:
SQL> connect rcat/rcat@rcat
SQL> select db_key, dbid, name from rc_database;
See Recipe 10-3 for more details regarding methods to identify your DBID.
Determining the Database Identifier
Problem
You've experienced media failure with all of your control files. Your backup strategy doesn't take advantage of either a
FRA or a recovery catalog. You're trying to restore a control file as follows:
$ rman target /
RMAN> startup nomount;
RMAN> restore controlfile from autobackup;
However, you receive an error message stating that you must explicitly set the database identifier (DBID):
RMAN-06495: must explicitly specify DBID with SET DBID command
You don't know the DBID for your database, and you aren't sure how to find the DBID. Without a control file for
your database, you can't mount the database and query the DBID value from the V$DATABASE view.
