15.10 - Dictionary Cache - Teradata Database

Teradata Database SQL Request and Transaction Processing

Teradata Database
Programming Reference
User Guide

The dictionary cache is a buffer that stores the non‑demographic Data Dictionary information most recently used to process SQL queries. Teradata Database caches the most recently used statistics and demographic data in the statistics cache (see “Statistics Cache” on page 22).

Teradata Database uses information from the Data Dictionary about privileges, tables, columns, views, macros, triggers, stored procedures, and other objects to transform an SQL request into the AMP steps needed to process a request. For information about AMP steps, see “OptApply” on page 67.

Caching Data Dictionary information reduces the I/O operations Teradata Database required to perform the following actions:

  • Resolve database object names
  • Validate object and row‑level security privileges
  • If an SQL request modifies the contents of the Data Dictionary, Teradata Database sends a spoil message to every PE on the system, directing them to drop the modified definitions from their respective dictionary caches.

    Teradata Database purges the dictionary cache periodically, one PE at a time.

    For the current default and maximum sizes of the dictionary cache, see the documentation for the DBS Control field DictionaryCacheSize in Utilities.