In addition, you can specify a range using SCNs
or log sequence numbers.
Incremental Backups
An alternative strategy to relying on full backups with archived redo logs is to use incremental
backups along with archived redo logs for recovery. The initial incremental backup is known as
a level 0 incremental backup. Each incremental backup after the initial incremental backup (also
known as a level 1 incremental backup) contains only changed blocks and as a result takes less
time and space. Incremental level 1 backups can either be cumulative or differential. A cumulative
backup records all changed blocks since the initial incremental backup; a differential backup
records all changed blocks since the last incremental backup, whether it was a level 0 or a level
1 incremental backup.
When a number of different types of backups exist in the catalog, such as image copies,
tablespace backupsets, and incremental backups, RMAN will choose the best combination of
backups to most efficiently recover and restore the database. The DBA still has the option to
prevent RMAN from using a particular backup (for example, if the DBA thinks that a particular
backup is corrupt and will be rejected by RMAN during the recovery operation).
The decision whether to use cumulative or differential backups is based partly on where you
want to spend the CPU cycles, and how much disk space you have available. Using cumulative
backups means that each incremental backup will become progressively larger and take longer
until another level 0 incremental backup is performed, but during a restore and recover operation,
only two backupsets will be required.
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