Recovering with Incrementally Updated Backups
You can apply incremental backups to your datafile
image copies when you use the RMAN. This takes much less time than
performing a full image copy of the datafiles every day.
This is applied through two phases:
1. Apply the incremental backups to datafile image
copies. This is done at the database block level.
2. Then apply the archive logs since the last
incremental backup only. This is done at the transaction level
(slower than previous phase).
To implement this option, you do the following steps:
1. Use the BACKUP INCREMENTAL LEVEL 1...FOR RECOVER
OF COPY WITH TAG ... form of the BACKUP command to create
incremental backups that can be incrementally updated. If an
incremental level 0 backup does not already exist, then
executing this command creates a level 0 backup with the
specified tag.
2. Apply any incremental backups to a set of data
file copies with the same tag using the RECOVER COPY ...WITH TAG
... form of the BACKUP command. Tags must be used to identify
the incremental backups and data file copies created for use in this
strategy, so that they do not interfere with other backup
strategies that you implement.
Fast Incremental Backups
• RMAN reads change tracking file to find out which
data blocks to read and copy during an incremental backup process,
to avoid needing to read entire datafiles during incremental
backups.
• A new background process, the change tracking
writer (CTWR), is in charge of writing the block change information
to the change tracking file.
Change Tracking File Features
• The change tracking file contains the physical
location of all database changes.
• The minimum size is 10MB. Oracle creates the file
automatically and allocates additional space in 10MB increments.
• The file’s size depends on your database size,
number of instances in an RAC, and the number of old backups the
file maintains.
• V$BLOCK_CHANGE_TRACKING shows the name, size, and
status of your change tracking file.
Enabling Block Change Tracking
