Recovery Catalog Role

The Oracle Recovery Catalog still has a role in Oracle 19c It remains a crucial component for robust backup and recovery management.
Here is why it's still important:

• Centralized Repository: It provides a central repository for storing metadata about your database backups, archives, and other recovery-related information. This is especially valuable in environments with multiple databases.
• Offloaded Metadata: By storing metadata separately from the target database control file, it offers redundancy and protection against control file corruption or loss.
• Historical Tracking: It retains a more extensive history of backups and archives than the control file, enabling recovery to older points in time.
• Enhanced Functionality: Certain RMAN features, like stored scripts for complex recovery procedures, rely on a recovery catalog.
• Improved Performance: For large databases, using a recovery catalog can improve RMAN performance by speeding up metadata queries and operations.

While some features like Data Recovery Advisor (DRA) have been deprecated in 19c, the core functionality and benefits of the Recovery Catalog remain intact.
Oracle continues to support and recommend the use of a Recovery Catalog for comprehensive backup and recovery management in Oracle 19c and beyond. It's a best practice for ensuring the recoverability and protection of your critical database environments. From earlier lessons, you should now have an understanding of the recovery catalog. This lesson will further discuss the role of the recovery catalog.

The recovery catalog is an optional Oracle database and is treated like any other Oracle database, so you must include it in your backup plans. The recovery catalog is a set of tables stored in a special schema and maintained by Recovery Manager. These tables contain information about any backup, restore, or recovery operations. The recovery catalog stores the following information:

1. Data file and archive log backup sets and the individual backup pieces
2. Image copy information
3. Archive redo logs and copy information
4. Stored scripts
5. Production database registration information
6. Control file information, especially physical schema information

• Why use a recovery catalog?
  There are several reasons to use a recovery catalog. The primary reason is the ability to have Recovery Manager maintain information about your backups and also know which backup sets to restore in the event of a failure. Also, Oracle recommends that you use a recovery catalog.
  Other important reasons include
  1. corruption detection,
  2. stored scripts for common activities,
  3. tablespace point-in-time recovery, and
  4. cumulative or noncumulative incremental backups.

The primary reason not to use a recovery catalog is that it may be unnecessary overhead or impractical. For instance, you would not use a recovery catalog for the databases on a laptop, which typically has a much less reliable disk system. If your disk dies, everything dies. Of course, you may not want or need store scripts or tablespace point-in-time recovery.
There are a number of other factors to consider with regard to your recovery catalog. Though these may seem obvious, it does not hurt to reinforce what you already know.
Review the Oracle backup and recovery documentation that provides some basic sizing information for your recovery catalog.

Because sizing a recovery catalog is not an exact science, the following table, included in some Oracle documentation, should be used with caution. If a separate database is created for the recovery catalog, use these guidelines for one year's space requirements for one production database. The following table contains legacy information which applied to Oracle 8, but does not apply to later versions of Oracle because the computing capabilities of the succeeding servers are able to accomodate more

1. disk space
2. ram and
3. CPU (processing power) .

Recommendation is three groups with two members per group.
As you can see from this table, the space requirements for a recovery catalog are fairly small, between 75MB and 100MB.

• RMAN Architecture: You can start performing backups with RMAN without installing or configuring any components. Simply invoke the RMAN client by using the RMAN executable (named rman) from the $ORACLE_HOME/bin directory, and you are ready to initiate backup. Just specify the target database you want to work with at the command line. You can perform backup and recovery actions with RMAN through the RMAN client or through the Enterprise Manager GUI. In addition to the RMAN client, you may use additional optional components to make your backup and recovery strategy robust and easy.
• Recovery catalog: The target database control file will always store the RMAN repository, which is the set of RMAN-related backup and recovery information. This data is also referred to as RMAN's metadata. However, it is smarter to use a dedicated database to store the RMAN repository. You can then create a special schema called the recovery catalog in this dedicated database and have RMAN store its repository in it, thus avoiding the risk of the critical metadata being overwritten when the control file runs out of space. As you will see, using a recovery catalog has several other advantages.
• Media management layer: As mentioned earlier, RMAN can directly interact only with disk drives. If you want to use tape drives to store your backups, you will need a media management layer in addition to RMAN, since RMAN cannot directly interact with the tape drives. You can use any of several Oracle-certified third-party media management layers. Oracle also provides Oracle Secure Backup, which it claims is the "most well-integrated media management layer for RMAN backups. Together, RMAN and Oracle Secure Backup provide a complete end-to-end backup solution for all Oracle environments.
• RMAN session in Unix/Linux systems An RMAN session in Unix/Linux systems consists of the following processes:
  1. The RMAN client process.
  2. A default channel, which is the connection to the target database.
  3. Additional channels you allocate and the corresponding target connection to each of the target databases.
  4. If you’re using the recovery catalog, there will be a catalog connection to the recovery catalog database.
  5. During database duplication or TSPITR operations, there will be an auxiliary connection to the auxiliary instance.
  6. By default, RMAN makes one polling connection to each of the target databases to help monitor the execution of RMAN commands on the different allocated channels.

In the next lesson, you will learn how to create a recovery catalog.