Oracle Incremental backup mechanism

There are two types of Incremental Backup in RMAN: Differential Mode and Cumulative mode. The backup level is divided into 0, 1, 2, 3, and 4, and the Level 0 is the highest.

Differential backup Differential (for superior-level or even level-level backup ):

Resolution: Level 0 backup (full backup) created last Sunday and level 2 Incremental Backup created on Monday. After the backup created on Sunday, back up data blocks modified at the current time. Tuesday is also an incremental backup. Therefore, you only need to back up the data blocks modified after the backup set created on Monday. By Wednesday, the level-1 backup must be backed up after the backup operation on Sunday and all modifications made to the current day. Both Thursday, Friday, and Saturday are two-level backups. You only need to back up the modifications that occurred after the backup operation on the previous day. It is not until Sunday that a new backup of level 0 is created again.

Cumulative Incremental Backup Cumulative (only recognized by the superior backup ):

Resolution: it is also a zero-level Incremental Backup created on Sunday, a two-level Incremental Backup created on Monday, and a two-level Incremental Backup created on Tuesday, however, when creating an incremental backup on Tuesday, the system does not care about Level 2 Incremental backup of the previous day. Instead, it backs up all the modified data blocks after the backup operation is performed on last Sunday. The Level 1 backup created on Wednesday only recognizes higher-level backup and also the modification that occurred after the backup from last Sunday. Similarly, the level 2 Incremental Backup created on Thursday is based on the Incremental backup on Wednesday. Both Friday and Saturday are two-level incremental backups, but they both ignore the incremental backups created at the same level the previous day and directly back up the modifications that occurred after Wednesday based on the first-level Incremental backup on Wednesday, until Sunday, another 0-level backup was made.

Note:

1. the BACKUP command defaults to Differential without displaying the specified information. However, from the perspective of recovery efficiency, Cumulative backup performs better without reading too many backup sets.

2. If the backup is not level 0 at the beginning, other backup levels other than level 0 will be automatically created.

3. the incremental backups before Oracle10g are of the 0, 1, 2, 3, and 4 levels.

4. There are only 0 and 1 levels in Oracle10g official documents, but multiple levels can still be specified in actual execution.