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Lesson 8 Data dictionary views
Objective Describe some of the V$ data dictionary views for backup and recovery.


Data Dictionary Views

The table below describes some of the system data dictionary views. These views assist in the management of the recovery catalog and its metadata[1].

Performance View Name Description
V$ARCHIVED_LOG This view maintains information about archived redo log files.
V$BACKUP_DATAFILE This view lists information about control files within backup sets.
V$BACKUP_CORRUPTION This view lists corrupt block ranges within datafile backups.
V$BACKUP_DATAFILE This view lists information about datafiles within backup sets.
V$BACKUP_DEVICE This view displays information on supported backup devices.
V$BACKUP_PIECE This view displays information on the backup pieces from control file.
V$BACKUP_REDOLOG This view displays information about archived logs within backup sets from the control file.
V$BACKUP_SET This view displays backup set information from control file.
V$COPY_CORRUPTION This view lists corrupt block ranges within datafile copies.

Purpose of Recovery Catalog Views and Database Data Dictionary Views

Similar to the Oracle database data dictionary tables, there are a number of recovery catalog views that are created when the recovery catalog is created. The naming convention for these views follows the convention of RC_*. For example, there are views called
  1. RC_BACKUP_SET and
along with other views.
Keep in mind that almost every RMAN operation is independent of the recovery catalog. Therefore, a number of V$ views in the database provide RMAN metadata similar to what is stored in the database control file.
The big difference between the database recovery catalog base tables and views and the related V$ views is the fact that the recovery catalog views will contain information on all the databases contained in the recovery catalog. This can be a security issue, which is addressed by the Virtual Private Catalog features .
You will find slight differences in the V$ views and recovery catalog views. For example, the primary keys for the records in the V$ views are going to be different from the primary key values in the recovery catalog. Again, this is because there are likely to be many more databases in the recovery catalog. You will find that there may well be more records in the recovery catalog than in the V$ views for a given database. This is because some records in the recovery catalog may have a retention requirement that is longer than the control file is able to maintain a record for. The database control file can only hold a year's worth of RMAN backup metadata, whereas the recovery catalog can hold this metadata forever. Therefore, it is quite likely that the recovery catalog records will be much larger than those within the control file.
[1]Metadata: The system tables and views of Oracle are metadata of the database.