Databases Reference
In-Depth Information
■
you must connect as
target
to a mounted or open database. to the recovery catalog database, you must
connect as
catalog
.
Note
■
Full resynchronization uses a snapshot of the target database control file as the source to resynchronize the
recovery catalog.
Note
How It Works
To update the recovery catalog using the current control file information, RMAN will first create a snapshot control
file. It'll then compare the contents of the recovery catalog to the contents of the snapshot control file and update the
recovery catalog by adding the missing information and modifying the changed backup- and schema-related records.
How often you must use the
resync catalog
command will depend on your backup frequency as well as the
number of archived redo logs and online log switches produced by the target database. At the least, you must ensure
that you resynchronize the recovery catalog often enough that the data in the control file gets transferred to the
recovery catalog before that data is overwritten because the control file is full. This means you must keep the value
of the initialization parameter
control_file_record_keep_time
longer than your backup interval. This is also a good
reason you must never set the value of this parameter to 0.
Two basic types of records get updated in the recovery catalog during the resynchronization process. The first
type of records consists of mostly archive log and backup-related data, such as the following:
•
Online log switch information
•
Archived redo log information
•
Backup history, such as backup sets, backup pieces, and proxy copies
•
Database incarnation history
The other major type of recovery catalog data that's updated is data relating to the
physical schema
, such as data
relating to data files and tablespaces, for example. When you issue certain RMAN commands such as the
backup
command, RMAN automatically performs a resynchronization. A resynchronization involves the comparison of the
recovery catalog to the current control file and the updating of the recovery catalog with the information that is either
missing or changed. A resynchronization is said to be
partial
when RMAN updates only information about archived
redo logs and new backups. During a
full
synchronization, in addition to the backup-related information, RMAN also
updates metadata about the physical schema, such as tablespaces, data files, online redo logs, and undo segments.
Thus, RMAN performs a full resynchronization whenever the schema metadata is changed; otherwise, it does only a
partial synchronization.
Although RMAN automatically resynchronizes the recovery catalog pursuant to most RMAN commands, such
as
backup
and
delete
, it is easy to think of situations when you may not be able to avail of this feature. For example,
you may decide to perform the backups of a database without connecting to the catalog database, or you may be
prevented from connecting to the recovery catalog database before the backup of a target database. Clearly, in such
cases, the control file will contain the backup information but not the recovery catalog, since you weren't even
connected to the recovery catalog during the backup of the target database. In cases such as these, you must connect
to the recovery catalog when you get a chance and perform a resynchronization using the
resync catalog
command.
Another scenario requiring you to resort to the manual resynchronization of the recovery catalog is when you
don't perform frequent backups, such as a nightly backup, but instead perform, say, a weekly or monthly backup.
If you were to perform a daily backup, RMAN would've automatically synchronized the recovery catalog as part of
