Backup Compression Algorithm
RMAN supports binary compression of backup sets.
The supported algorithms are BZIP2 (default) and ZLIB.
The BZIP2 algorithm is optimized for maximum compression, whereas the ZLIB algorithm is optimized for CPU efficiency.
BZIP2 consumes more CPU resource than ZLIB, but will usually produce more compact backups.
The COMPATIBLE initialization parameter must be set to 11.0.0 or higher for ZLIB compression, which requires the Oracle Advanced Compression option.
You can configure the compression algorithm with the following syntax, where alg_name is a placeholder specifying either BZIP2 or ZLIB.
How to Configure the Backup Compression Algorithm
CONFIGURE COMPRESSION ALGORITHM TO ‘alg_name';
We can use v$rman_compression_algorithm view to check.
ALGORITHM_ ALGORITHM_DESCRIPTION
———- ——————————
BZIP2 good compression ratio
BASIC good compression ratio
LOW maximum possible compression speed
ZLIB balance between speed and compression ratio
MEDIUM balance between speed and compression ratio
HIGH maximum possible compression ratio
———- ——————————
BZIP2 good compression ratio
BASIC good compression ratio
LOW maximum possible compression speed
ZLIB balance between speed and compression ratio
MEDIUM balance between speed and compression ratio
HIGH maximum possible compression ratio
It’s possible Basic means BZIP2 because they have the same description, and Medium means ZLIB.
From x$ksppi, parameter _backup_lzo_size means “specifies buffer size for LOW compression” so we know Low means LZO.