You can query this catalog for critical information, such as datafiles that have not
been backed up or datafiles whose backups have been invalidated through
NOLOGGING operations performed on objects contained in those datafiles.
RMAN also uses the catalog to perform incremental backups. RMAN will back up
only database blocks that have changed since the last backup. When RMAN backs
up only the individual changed blocks in the database, the overall backup and recovery
time can be significantly reduced for databases in which a small percentage of the
data in large tables changes. Since Oracle Database 10g, RMAN can apply incremental
backups to an image backup of the database. Improvements in methods used by
RMAN in recent Oracle releases have greatly enhanced performance for incremental
backups.
RMAN reads and writes Oracle blocks, not operating system blocks. While RMAN
is backing up a datafile, Oracle blocks can be written to it, but RMAN will read and
write in consistent Oracle blocks, not operating system blocks within an Oracle
block.
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