Database Reference
In-Depth Information
If you need to clear the device-type compression, issue this command:
RMAN> configure device type disk clear;
I've found the default compression algorithm to be quite efficient. For a typical database the backups are usually
approximately four to five times smaller than the regular backups. Of course, your compression results may vary,
depending on your data.
Why not compress all backups? Compressed backups consume more CPU resources and take longer to create
and restore from, but they result in less I/O, spread out over a longer period. If you have multiple CPUs, and the speed
of making a backup isn't an issue, then you should consider compressing your backups.
You can view the type of compression enabled, using the
SHOW
command:
RMAN> show compression algorithm;
Here is some sample output:
CONFIGURE COMPRESSION ALGORITHM 'BASIC' AS OF RELEASE 'DEFAULT'
OPTIMIZE FOR LOAD TRUE ; # default
The basic compression algorithm doesn't require an extra license from Oracle. If you're using Oracle 11g Release
2 or higher, and if you have a license for the Advanced Compression option, then you have available three additional
configurable levels of binary compression; for example,
RMAN> configure compression algorithm 'HIGH';
RMAN> configure compression algorithm 'MEDIUM';
RMAN> configure compression algorithm 'LOW';
In my experience the prior compression algorithms are very efficient, both in compression ratios and time taken
to create backups.
You can query
V$RMAN_COMPRESSION_ALGORITHM
to view details regarding the compression algorithms available
for your release of the database. To reset the current compression algorithm to the default of
BASIC
, use the
CLEAR
command:
RMAN> configure compression algorithm clear;
21. Configuring Encryption
You may be required to encrypt backups. Some shops especially require this for backups that contain sensitive data
and that are stored offsite. To use encryption when backing up, you must use the Oracle Enterprise Edition, possess a
license for the Advanced Security option, and use Oracle 10g Release 2 or higher.
If you've configured a security wallet (see the
Oracle Advanced Security Administrator's Guide
, which can be
freely downloaded from the Technology Network area of the Oracle website (
http://otn.oracle.com
,
for details),
you can configure transparent encryption for backups, as shown:
RMAN> configure encryption for database on;
Any backups that you make now will be encrypted. If you need to restore from a backup, it's automatically
unencrypted (assuming the same security wallet is in place as when you encrypted the backup). To disable
encryption, use the
CONFIGURE
command:
RMAN> configure encryption for database off;
