The recovery catalog contains information about both RMAN backups and the target database. More specifically, the recovery catalog contains the following:
- RMAN configuration settings
- RMAN-stored scripts that you create
- Target database tablespace and data file information
- Information pertaining to data file backup sets and backup pieces
- Information pertaining to archived redo log backup sets and backup pieces
- Information pertaining to data files and archived redo log copies.
You can create the recovery catalog in a target database that you want to back up using the recovery catalog, but that’s an unwise choice! In such a case, losing the target database means you’ve lost the recovery catalog as well, thus making recovery much harder or even impossible. It’s a good policy to back up the recovery catalog right after you back up the target databases.
 The owner of a recovery catalog, called the recovery catalog owner, can grant restricted access of the recovery catalog to other users. The restricted access is called a virtual private catalog. The main or central recovery catalog that acts as the repository for all databases is called the base recovery catalog. The owner of the base recovery catalog determines which databases the virtual catalog owner can access. There can be multiple virtual catalogs but there should be only one base recovery catalog. Oracle recommends creating one central recovery catalog to act as the repository for all your databases.
The most important factor when determining the size of the recovery catalog is the frequency of backups. Another key determinant of the size of the recovery catalog is the number of archived redo logs produced by each database.
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