What is resynchronization of a recovery catalog?

What is resynchronization of a recovery catalog?

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A recovery catalog obtains the metadata about a target database from the target database's control file. Recovery Manager (RMAN) is responsible for propagating the metadata into the recovery catalog from the target database's control file. Resynchronization of the recovery catalog ensures that the metadata in the recovery catalog is synchronized with the metadata in the control file.

Resynchronization of a recovery catalog can be partial or full. In a partial resynchronization, RMAN reads the current control file to update the recovery catalog with the changed information about new backups, new archived redo logs, etc. However, RMAN does not update the recovery catalog with the changed information about the database's physical structure, such as data files, tablespaces, redo threads, rollback segments, and online redo logs. In a full resynchronization, on the other hand, RMAN updates the recovery catalog with all the changed information, including information about physical structures.

While resynchronizing the recovery catalog, RMAN creates a snapshot of the target database's control file, compares the recovery catalog with the snapshot, and updates the recovery catalog with the information that is missing or changed.

RMAN automatically performs a full or partial resynchronization of a recovery catalog as needed when certain commands, including BACKUP, COPY, and DELETE, are executed. However, a manual resynchronization may be required in the following scenarios:

After a log switch occurs.

After a redo log is archived.

After a tablespace is added or removed from the target database.

After a data file is added or removed from a tablespace in the target database.

After a rollback segment is added or removed from the target database.

A manual resynchronization is required in the above scenarios because RMAN does not automatically update the recovery catalog in these scenarios. A manual resynchronization can be performed by executing the RESYNC CATALOG command. The RESYNC CATALOG command forces the Recovery Manager to perform a full resynchronization of the recovery catalog.

Resynchronization of a recovery catalog is required only when the changes are made to the target database. Changes made to the recovery catalog database (database containing the recovery catalog) do not require a resynchronization of the recovery catalog.

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