11g RMAN Compression algorithms

When using the RMAN compression feature, you can choose among different compression algorithms. You can query the view V$RMAN_COMPRESSION_ALGORITHM to view the compression algorithms available to you:

SQL> select algorithm_name,algorithm_description, is_default from v$rman_compression_algorithm;
ALGORITHM ALGORITHM DESCRIPTION IS_DEFAULT
—————————————————————- —
ZLIB fast but little worse compression ratio YES
BZIP2 good compression ratio but little slower NO

As the query shows, the ZLIB compression algorithm offers speed but not a good compression ratio. The alternate compression algorithm, BZIP2, is slower but provides a better compression ratio. You can use the show command to check the current compression algorithm in use:

RMAN> show compression algorithm;
RMAN configuration parameters are:
CONFIGURE COMPRESSION ALGORITHM ‘ZLIB’; # default
RMAN>
■Note If you set the compatible initialization parameter to 11.1 or newer, ZLIB will be the default compression algorithm. You can’t choose the compression algorithm if you set the compatible parameter to anything older than 11.0.

Remember that the choice of the compression algorithm is available only in Oracle Database 11g. In earlier versions of the database, you only have a single choice—the default algorithm BZIP2.

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