RMAN Incremental backup

This backups only datafile blocks changed since specified previous backup.

1.This strategy could be followed to make incrementally updated backup .These incrementally updated backup will be used to make updated image copy will all roll forward image.

2.Reduce amount of time to take backup.

3.Save network bandwidth

  1. To be able to recover changes to objects created with the NOLOGGING option. For example, direct load inserts do not create redo log entries and their changes cannot be reproduced with media recovery. They do, however, change data blocks and so are captured by incremental backups.
  2. To reduce backup sizes for NOARCHIVELOG databases. Instead of making a whole database backup every time, you can make incremental backups.

As with full backups, if you are in ARCHIVELOG mode, you can make incremental backups if the database is open; if the database is in NOARCHIVELOG mode, then you can only make incremental backups after a consistent shutdown.

Level 0 and Level 1 Incremental Backups

Level 0 incremental backup will register all copies of block which has data.This is base for incremental backup .

Difference between full and level 0 backup is:

Level 0 backup will involve in incremental backup strategy.

Why cumulative backup are useful than differential

Cumulative backups are preferable to differential backups when recovery time is more important than disk space, because during recovery each differential backup must be applied in succession. Use cumulative incremental backups instead of differential, if enough disk space is available to store cumulative incremental backups.

 

Differential Incremental Backups

RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;

 

  • Sunday

An incremental level 0 backup backs up all blocks that have ever been in use in this database.

  • Monday – Saturday

On each day from Monday through Saturday, a differential incremental level 1 backup backs up all blocks that have changed since the most recent incremental backup at level 1 or 0. So, the Monday backup copies blocks changed since Sunday level 0 backup, the Tuesday backup copies blocks changed since the Monday level 1 backup, and so forth.

  • The cycle is repeated for the next week.

Cumulative Incremental Backups

BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE; # blocks changed since level 0

In the example shown in the following occurs:

  • Sunday

An incremental level 0 backup backs up all blocks that have ever been in use in this database.

  • Monday – Saturday

A cumulative incremental level 1 backup copies all blocks changed since the most recent level 0 backup. Because the most recent level 0 backup was created on Sunday, the level 1 backup on each day Monday through Saturday backs up all blocks changed since the Sunday backup.

  • The cycle is repeated for the next week.

Basic incremetal Backup strategy

you can implement a three-level backup scheme so that a full or level 0 backup is taken monthly, a cumulative level 1 is taken weekly, and a differential level 1 is taken daily. In this scheme, you never have to apply more than a day’s worth of redo for complete recovery.

Making Incremental Backups: BACKUP INCREMENTAL

After starting RMAN, run the BACKUP INCREMENTAL command at the RMAN prompt. This example makes a level 0 incremental backup of the database:

BACKUP INCREMENTAL LEVEL 0 DATABASE;

This example makes a differential level 1 backup of the SYSTEM tablespace and datafile tools01.dbf. It will only back up those data blocks changed since the most recent level 1 or level 0 backup:

BACKUP INCREMENTAL LEVEL 1  TABLESPACE SYSTEM  DATAFILE ‘ora_home/oradata/trgt/tools01.dbf’;

This example makes a cumulative level 1 backup of the tablespace users, backing up all blocks changed since the most recent level 0 backup.

BACKUP INCREMENTAL LEVEL = 1 CUMULATIVE  TABLESPACE users;

 

Enabling and Disabling Change Tracking to improve performance of incremental backup

To store the change tracking file in the database area, set DB_CREATE_FILE_DEST in the target database. Then issue the following SQL statement to enable change tracking:

SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;

You can also create the change tracking file in a location you choose yourself, using the following SQL statement:

SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING   USING FILE ‘/mydir/rman_change_track.f’ REUSE;

The REUSE option tells Oracle to overwrite any existing file with the specified name.

To disable change tracking, use this SQL statement:

SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

If the change tracking file was stored in the database area, then it is deleted when you disable change tracking.

Checking Whether Change Tracking is Enabled

From SQL*Plus, you can query V$BLOCK_CHANGE_TRACKING.STATUS to determine whether change tracking is enabled, and if it is, query V$BLOCK_CHANGE_TRACKING.FILENAME to display the filename.

 

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