17.10 - CompressionAlgorithm - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - Database Utilities

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Release Date
July 2021
Content Type
Configuration
Publication ID
B035-1102-171K
Language
English (United States)

Specifies the algorithm that is used to compress and decompress data in file system data blocks.

Field Group

Compression

Valid Settings

Setting Description
ZLIB ZLIB lossless data compression and decompression algorithms.
ELZS_H Hardware-based Exar Lemple-Ziv-Stac lossless data compression and decompression algorithms.
This type of compression requires that compression engine hardware be installed on every system node.
ELZS_S Software-based Exar Lemple-Ziv-Stac lossless data compression and decompression algorithms.

This type of compression is used automatically if ELZS_H has been selected but problems are detected with the hardware compression engine board.

Explicitly setting this algorithm in DBS Control is not recommended, except when recovering from a hardware compression engine failure.

Default

ZLIB

Changes Take Effect

After the DBS Control Record has been written. Changed setting applies to new data added to tables. Compression for existing data is not changed until that data is modified.

Usage Notes

BLC enables data compression at the data block (DB) level of the Teradata file system. Compression reduces the amount of storage required for a given amount of data. The BlockLevelCompression field of DBS Control enables and disables BLC.

After a data block has been compressed using a particular algorithm, the data retains that compression, even if the algorithm is subsequently changed. New data added to the table is compressed using the new algorithm. If previously compressed data is updated, which requires uncompressing and recompressing the data, the currently set algorithm is used for the recompression.

Consequently, a single subtable can exhibit a mixture of uncompressed data blocks and data blocks compressed using different compression algorithms, depending on the settings at the time the data was added to the table. To make the data consistent with respect to compression, use the Ferret COMPRESS command to compress all the data using the currently set algorithm, or use the Ferret UNCOMPRESS command to uncompress all the table data.

Related Information

For more information on... See...
BlockLevelCompression field BlockLevelCompression.
ZLIB data compression algorithm http://zlib.net.
Lempel-Ziv-Stac data compression algorithm http://en.wikipedia.org/wiki/Lempel-Ziv-Stac.
COMPRESS and UNCOMPRESS commands Ferret Utility (ferret).
BLOCKCOMPRESSION query band Teradata Vantage™ - SQL Data Definition Language Syntax and Examples, B035-1144.