COMPRESSION

Default: DISABLED

Purpose

Specifies whether to compress data (and optionally, which compression algorithm to use) before the data is written to the dump file set.

Syntax and Description

COMPRESSION [ENABLED {BASIC | LOW| MEDIUM | HIGH} | DISABLED]

  • If ENABLED is specified, then all data is compressed for the entire unload operation. You can additionally specify one of the following compression options:

    • BASIC - Offers a good combination of compression ratios and speed; the algorithm used is the same as in previous versions of Oracle Data Pump.

    • LOW - Least impact on unload throughput and suited for environments where CPU resources are the limiting factor.

    • MEDIUM - Recommended for most environments. This option, like the BASIC option, provides a good combination of compression ratios and speed, but it uses a different algorithm than BASIC.

    • HIGH - Best suited for unloads over slower networks where the limiting factor is network speed.

    Note:

    To use these compression algorithms, the COMPATIBLE initialization parameter must be set to at least 12.0.0. This feature requires that the Oracle Advanced Compression option be enabled.

    The performance of a compression algorithm is characterized by its CPU usage and by the compression ratio (the size of the compressed output as a percentage of the uncompressed input). These measures vary on the size and type of inputs as well as the speed of the compression algorithms used. The compression ratio generally increases from low to high, with a trade-off of potentially consuming more CPU resources.

    It is recommended that you run tests with the different compression levels on the data in your environment. Choosing a compression level based on your environment, workload characteristics, and size and type of data is the only way to ensure that the exported dump file set compression level meets your performance and storage requirements.

  • If DISABLED is specified, then no data is compressed for the upload operation.

Example

In the following example, the COMPRESSION parameter is set to ENABLED. Therefore, all data written to the dept.dmp dump file will be in compressed format.

CREATE TABLE deptXTec3
 ORGANIZATION EXTERNAL (TYPE ORACLE_DATAPUMP DEFAULT DIRECTORY def_dir1
 ACCESS PARAMETERS (COMPRESSION ENABLED) LOCATION ('dept.dmp'));