RMAN Backups and Reporting - Oracle RMAN for Absolute Beginners - page 134

The third time you run the incrementally updating backup, it does this:

• Now that an incremental backup has been created, the

RECOVER COPY applies the incremental

backup to the image copies.

BACKUP INCREMENTAL makes an incremental level 1 backup and assigns it the tag name
specified; this backup will subsequently be used by the RECOVER COPY command.
Going forward, each time you run the two lines of code, you will have a regularly repeating backup pattern. If you
use image copies for backups, you might consider using an incrementally updating backup strategy, because with
it, you avoid creating entire image copies whenever the backup runs. The image copies are updated each time the
backup runs with the incremental changes from the previous backup.

•

Using Block Change Tracking
Block change tracking is the process in which a binary file is used to record changes to database data file blocks. The
idea is that incremental backup performance can be improved because RMAN can use the block change tracking file
to pinpoint which blocks have changed since the last backup. This saves a great deal of time because otherwise RMAN
would have to scan all the blocks that had been backed up to determine if they'd changed since the last backup.
Listed next are the steps for enabling block change tracking:

1. If not already enabled, set the DB_CREATE_FILE_DEST parameter to a location (that already

exists on disk); for example,

SQL> alter system set db_create_file_dest='/u01/O12C/bct' scope=both;

2. Enable block change tracking via the ALTER DATABASE command:

SQL> alter database enable block change tracking;
This example creates a file with an OMF name in the directory specified by DB_CREATE_FILE_DEST . In this
example the file created is given this name:

/u01/O12C/bct/O12C/changetracking/o1_mf_8h0wmng1_.chg

You can also enable block change tracking by directly specifying a file name, which does not require that
DB_CREATE_FILE_DEST be set; for example,

SQL> alter database enable block change tracking using file '/u01/O12C/bct/btc.bt';

You can verify the details of block change tracking by running the following query:

SQL> select * from v$block_change_tracking;

For space-planning purposes, the size of the block change tracking file is approximately 1/30,000 the size of
the total size of the blocks being tracked in the database. Therefore, the size of the block change tracking file is
proportional to the size of the database and not to the amount of redo generated.
To disable block change tracking, run this command:

SQL> alter database disable block change tracking;