Block-Level Compression | Database Design | Teradata Vantage - 17.10 - Block-Level Compression - Advanced SQL Engine - Teradata Database

Teradata Vantageā„¢ - Database Design

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Release Date
July 2021
Content Type
User Guide
Publication ID
B035-1094-171K
Language
English (United States)
A data block is a physical unit of I/O that defines how Vantage handles data. When you specify block-level compression (BLC), Vantage stores data blocks in compressed format to save storage space. BLC can be enabled or disabled system-wide or for specific types of tables only. BLC can be applied to these objects:
  • Journal tables
  • Join indexes
  • Hash indexes
  • Spool tables
  • Global temporary tables
  • Primary subtables
  • Fallback subtables
  • LOB subtables (JSON, XML, and character)
Block-level compression is independent of any other type of compression applied to the same data.

The goals of block-level compression are to save storage space and to reduce disk I/O bandwidth. Block-level compression can use significantly more CPU to compress and decompress data dynamically, so whether query performance is enhanced with block-level compression depends on whether performance is more limited by disk I/O bandwidth or CPU usage.

Teradata offers software-based and hardware-based BLC. You select the BLC method when you specify the compression algorithm in the CompressionAlgorithm field in DBS Control. See Controlling BLC at the System Level Using the DBS Control Utility.

The following site provides guidelines for evaluating the impact of block-level compression on performance and on disk space: https://downloads.teradata.com/extensibility/articles/block-level-compression-evaluation-with-the-blc-utility. The site also provides a link to download the Block Level Compression Evaluation utility.