What is meant by incremental,cumulative and complete backups?

Full Backups
A full backup is different from a whole database backup. A full data file backup is a backup that includes every used data block in the file. RMAN copies all blocks into the backup set or image copy, skipping only data file blocks that hav
e never been used. For a full image copy, the entire file contents are reproduced exactly. A full backup cannot be part of an incremental backup strategy; it cannot be the parent for a subsequent incremental backup

Incremental Backups
An incremental backup is either a level 0 backup, which includes every block in the data files except blocks that have never been used, or a level 1 backup, which includes only those blocks that have been changed since a previous backup was taken. A level 0 incremental backup is physically identical to a full backup. The only difference is that the level 0 backup can be used as the base for a level 1 backup, but a full backup can never be used as the base for a level 1 backup.
Incremental backups are specified through the INCREMENTAL keyword of the BACKUP
command. You specify INCREMENTAL LEVEL = [0 | 1].

RMAN can create multilevel incremental backups as follows:
• Differential: The default type of incremental backup that backs up all blocks changed after the most recent incremental backup at either level 1 or level 0
• Cumulative: Backs up all blocks changed after the most recent backup at level 0

Examples
• To perform an incremental backup at level 0, use the following command:

RMAN> BACKUP INCREMENTAL LEVEL 0 DATABASE;

• To perform a differential incremental backup, use the following command:

RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;

• To perform a cumulative incremental backup, use the following command:

RMAN> BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE;

RMAN makes full backups by default if neither FULL nor INCREMENTAL is specified. Unused block compression causes never-written blocks to be skipped when backing up data files to backup sets, even for full backups.
A full backup has no effect on subsequent incremental backups, and is not considered part of any incremental backup strategy, although a full image copy backup can be incrementally updated by applying incremental backups with the RECOVER command.

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