Hash and Join Index Row Compression
When describing compression of hash and join indexes, compression refers to a logical row compression in which multiple sets of non-repeating column values are appended to a single set of repeating column values. This enables the system to store the repeating value set only once, while any non-repeating column values are stored as logical segmental extensions of the base repeating set.
Block-level compression, or BLC, is a lossless physical compression method that can be specified in a CREATE TABLE statement. Block-level compression can be applied to row-level security constraint columns, which are not eligible for multivalue compression and algorithmic compression.
For information about BLC and how the system applies compression to various types of tables, see Teradata Vantage™ - Database Utilities, B035-1102.
Autocompression for Column-Partitioned Tables
When describing system-selected autocompression of containers in column-partitioned tables, compression refers to various compression methods that Teradata Database can use to compress the column values of a container.