The document outlines four types of RMAN backup compression methods available in Oracle 11g and 12c: basic, low, medium, and high, with varying impacts on database performance and backup size. Advanced compression licenses are required for low, medium, and high options, and the compression is applied only when explicitly specified during backup. Testing results indicate that backup size and time can vary based on several factors, including channels and server configurations.

1. RMAN BACKUP
COMPRESSION
TYPES

2. Compression types
Both Oracle 11g and 12c has below 4 types of compression types:
BASIC: Its the basic compression method which is default configured
in rman parameters.
LOW: Lead compression method where DB performance and backup
size hold good.

3. MEDIUM: Recommended method as its the best combination of DB
performance and compression ratio.
HIGH: You get the highest backup compression but DB performance
and backup will be very slow.
Note: except BASIC compression, you need an advance compression
license to use LOW, MEDIUM and HIGH compression types.

4. Check compression type
Inside RMAN parameters, we have compression algorithm type
which defines the type of compression method to be used. You can
check it via below command
Note: default compression set to BASIC does not mean that every
backup that you trigger will be compressed.
The backup compression algorithm will only be used when you use
BACKUP AS COMPRESSED clause while taking the backups.

5. Change compression type
If you have the advance compression license, then you can always change to
other types of compression methods available.
You can always change compression algorithm to Low, Medium and High.

6. Testing backup
compression
When you use backup compression, you must know what are the benefits of it
and when to use the particular type of backup compression method.
In a test case, we tested backup compression on a small database and
below are our findings:

7. Note: the backup size and time might differ based on channels, server and
other factors.

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