DB2® Version 8: The Official Guide

Chapter 4. System Default Value and NULL Compression

In DB2 UDB v7.2, the record format used to store a table's data consumed a fixed amount of space for all columns, regardless of the data value for the column. There is a growing demand for all databases to consume less space. One of the ways that a database could save space is to not set aside a fixed amount of space if the column value is NULL, or by simply not hardening the column's value to disk if it can be easily known (e.g., system default values are always easily known and available to the DB2 UDB engine during record formatting and column extraction).

DB2 UDB v8.1 provides a new ability to compress NULLs and system default values, thereby storing this data more efficiently and reducing ...