17.05 - BLOCKCOMPRESSION - Advanced SQL Engine - Teradata Database

Table data is compressed at the block level.

You cannot specify this option to modify the definitions of global temporary tables or volatile tables.

For details, see CREATE TABLE in Teradata Vantage™ - SQL Data Definition Language Detailed Topics , B035-1184 .

AUTOTEMP

The file system determines the block-level compression setting for the table based on its Teradata Virtual Storage temperature.


Block-level compression is applied based on the temperature of the cylinders on which the data is stored. The file system determines the block-level compression setting for the table based on its Teradata Virtual Storage temperature. The definitions of the various thresholds are determined by the DBS Control field TempBLCThresh. For details, see Teradata Vantage™ - Database Utilities , B035-1102 . You can adjust the temperature values for data being loaded using SET QUERY_BAND. See Example: Setting BLOCKCOMPRESSION and TVSTEMPERATURE Query Bands.

MANUAL

Block-level compression is applied based on the default for the table at the time the table is created. The defaults for the table are determined by the settings in the Compression group of DBS Control fields. See Teradata Vantage™ - Database Utilities , B035-1102 . You can override these values using SET QUERY_BAND. See Example: Using the BLOCKCOMPRESSION Reserved Query Band.

Tables can be compressed or uncompressed at any time after loading by using the Ferret COMPRESS and UNCOMPRESS commands.

ALWAYS

The table and its subtables are always block-level compressed, even if a query band or the applicable DBS Control block-level compression settings indicate otherwise. The DBS Control field BlockLevelCompression must be enabled.

Tables can be compressed at any time after loading by using the Ferret COMPRESS command. This can be useful if this BLOCKCOMPRESSION option was set after the table was already populated.

NEVER

The table and its subtables are not block-level compressed, even if a query band or the applicable DBS Control block compression settings indicate otherwise.

Tables can be uncompressed at any time after loading by using the Ferret UNCOMPRESS command. This can be useful if this BLOCKCOMPRESSION option was set after the table was already populated.

DEFAULT

The table uses the block-level compression setting in the DBS Control field DefaultTableMode. For details, see Teradata Vantage™ - Database Utilities , B035-1102 .

BLOCKCOMPRESSIONALGORITHM

Specifies the algorithm to use for block-level compression (BLC).

This option only applies when the effective BLOCKCOMPRESSION is MANUAL, AUTOTEMP, or ALWAYS.

ZLIB

Block-level compression using the zlib software algorithm.

ELZS_H

Block-level compression using a hardware compression engine board in every system node.

DEFAULT

Uses the setting of the DBS Control field CompressionAlgorithm. See Teradata Vantage™ - Database Utilities , B035-1102 .

BLOCKCOMPRESSIONLEVEL

Specifies a value to indicate a preference for compression speed or compression effectiveness. This option only applies when the BLOCKCOMPRESSIONALGORITHM option is set to ZLIB. Although this option is accepted in combination with BLOCKCOMPRESSIONALGORITHM = ELZS_H, this option is ignored. If BLOCKCOMPRESSIONALGORITHM is altered to ZLIB, this option takes effect.

value

Integer from 1 through 9, where 1 specifies the least processor-intensive compression speed with the lowest compression ratio and 9 specifies the most processor-intensive compression speed with highest compression ratio.

DEFAULT

The table uses the compression level setting of the DBS Control field CompressionLevel. See Teradata Vantage™ - Database Utilities , B035-1102 .