SQL> select ALGORITHM_NAME, ALGORITHM_DESCRIPTION, ALGORITHM_COMPATIBILITY from V$RMAN_COMPRESSION_ALGORITHM ;
ALGORITHM_NAME ALGORITHM_DESCRIPTION ALGORITHM_COMPATIB
--------------- ------------------------------------------------------------ ------------------
BZIP2 good compression ratio 9.2.0.0.0
BASIC good compression ratio 9.2.0.0.0
LOW maximum possible compression speed 11.2.0.0.0
ZLIB balance between speed and compression ratio 11.0.0.0.0
MEDIUM balance between speed and compression ratio 11.0.0.0.0
HIGH maximum possible compression ratio 11.2.0.0.0
2，手工指定压缩算法
Q. Can I compress RMAN backups ?
A. RMAN supports binary compression of backup sets. The supported algorithms are BZIP2 (default) and ZLIB. Kindly refer Note 563427.1 for more details about different type of compressions. Its not recommend to compress the RMAN backup using any other OS or third party utility.
Note : RMAN compressed backup with BZIP2 provides great compression but is CPU intensive. Using ZLIB compression requires the Oracle Database 11g Advanced Compression Option and is only supported with an 11g database. The feature is not backward compatible with 10g databases.
3，推荐压缩算法？
Configuring Compression for Backups
You can optionally use compression when backing up Oracle databases to Oracle Database Backup Cloud Service. Compression conserves bandwidth by reducing the size of your backups before they’re sent to the cloud. You’ll specify compression when you perform a backup.
Recovery Manager (RMAN) supports binary compression using one of the following compression levels: HIGH, MEDIUM, BASIC, and LOW. The recommended level for cloud backups is MEDIUM.
For example, the following RMAN commands configure compression using the MEDIUM algorithm:
RMAN> CONFIGURE COMPRESSION ALGORITHM 'MEDIUM';
RMAN> CONFIGURE DEVICE TYPE sbt BACKUP TYPE TO COMPRESSED BACKUPSET;
4，默认压缩
About RMAN Default Compression
Use the CONFIGURE command to configure the default compression algorithm, which does not require the Oracle Advanced Compression option.
Example Configuring Basic Compression for Backup
The following example configures basic compression for RMAN backups..
CONFIGURE COMPRESSION ALGORITHM 'BASIC';
About Oracle Advanced Compression Option
If you have enabled the Oracle Advanced Compression option, you can choose from the compression levels listed in the following table.
Compression Level Performance Benefits and Trade-Offs
HIGH
Best suited for backups over slower networks where the limiting factor is network speed.
MEDIUM
Recommended for most environments. Good combination of compression ratios and speed.
LOW
Least effect on backup throughput.
The compression ratio generally increases from low to high, with a trade-off of potentially consuming more CPU resources.
Because the performance of the various compression levels depends on the nature of the data in the database, network configuration, system resources and the type of computer system and its capabilities, Oracle cannot document universally applicable performance statistics. Which level is best for your environment depends on how balanced your system is regarding bandwidth into the CPU and the actual speed of the CPU. It is highly recommended that you run tests with the different compression levels on the data in your environment. Choosing a compression level based on your environment, network traffic characteristics (workload), and data set is the only way to ensure that the backup set compression level can satisfy your organization's performance requirements and applicable service level agreements.
Customer RecommendedA Complete Understanding of RMAN Compression (Doc ID 563427.1)
RMAN -- Frequently Asked Question (FAQ) (Doc ID 469777.1)