Zone maps

Zone maps are automatically generated internal tables that the IBM® Netezza® system uses to improve the throughput and response time of SQL queries against large grouped or nearly ordered date, timestamp, byteint, smallint, integer, and bigint data types.

Zone maps reduce disk scan operations that are required to retrieve data by eliminating records outside the start and end range of a WHERE clause on restricted scan queries. The IBM Netezza Storage Manager uses zone maps to skip portions of tables that do not contain rows of interest and thus reduces the number of disk pages and extents to scan and the search time, disk contention, and disk I/O.