DDL and DCL Requests, Dictionary Access, and Locks | Teradata Vantage - DDL and DCL Requests, Dictionary Access, and Locks - Analytics Database - Teradata Vantage

The execution of a DDL or DCL request causes the data dictionary to be updated and appropriate locks to be placed on system tables while that request is processing.

Optimizing the Locking Granularity for Data Dictionary Access

To improve concurrency, DDL and DCL processing use the finest locking granularity that is practical and delay placing locks as long as possible. Depending on the dictionary table, the system may downgrade rowhash READ lock requests made on the dictionary to ACCESS locks to prevent the query from being blocked by WRITE locks placed on those tables by ongoing DDL operations.

If not blocked, these rowhash READs are not blocked use the standard READ locks.

These are system-initiated lock downgrades that you cannot specify using the LOCKING request modifier. See Teradata Vantage™ - SQL Data Manipulation Language, B035-1146.