The Dictionary Cache
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).
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.
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.