SAS/ACCESS 9.2 for Relational Databases: Reference, Fourth Edition

834 Understanding SAS/ACCESS Locking Options 4 Chapter 28effect. For a complete description of Teradata locking, see the LOCKING statement inyour Teradata SQL reference documentation.Understanding SAS/ACCESS Locking OptionsSAS/ACCESS locking options modify Teradata’s standard locking. Teradata usuallylocks at the row level; SAS/ACCESS lock options lock at the table or view level. Thechange in the scope of the lock from row to table affects concurrent access to DBMSobjects. Specifically, READ and WRITE table locks increase the time that other usersmust wait to access the table and can decrease overall system performance. Thesemeasures help minimize these negative effects.3 Apply READ or WRITE locks only when you must apply special locking onTeradata tables.SAS/ACCESS locking options can be appropriate for special situations, asdescribed in “When to Use SAS/ACCESS Locking Options” on page 834. IfSAS/ACCESS locking options do not meet your specialized needs, you can useadditional Teradata locking features using views. See CREATE VIEW in yourTeradata SQL reference documentation for details.3 Limit the span of the locks by using data set locking options instead of LIBNAMElocking options whenever possible. (LIBNAME options affect all tables that youopen that your libref references. Data set options apply only to the specified table.)If you specify these read locking options, SAS/ACCESS generates and submits toTeradata locking modifiers that contain the values that you specify for the three readlock options:3 READ_ISOLATION_LEVEL= specifies the level of isolation from other table usersthat is required during SAS/ACCESS read operations.3 READ_LOCK_TYPE= specifies and changes the scope of the Teradata lock duringSAS/ACCESS read operations.3 READ_MODE_WAIT= specifies during SAS/ACCESS read operations whetherTeradata should wait to acquire a lock or fail your request when the DBMSresource is locked by a different user.If you specify these update lock options, SAS/ACCESS generates and submits toTeradata locking modifiers that contain the values that you specify for the three updatelock options:3 UPDATE_ISOLATION_LEVEL= specifies the level of isolation from other tableusers that is required as SAS/ACCESS reads Teradata rows in preparation forupdating the rows.3 UPDATE_LOCK_TYPE= specifies and changes the scope of the Teradata lockduring SAS/ACCESS update operations.3 UPDATE_MODE_WAIT= specifies during SAS/ACCESS update operationswhether Teradata should wait to acquire a lock or fail your request when theDBMS resource is locked by a different user.When to Use SAS/ACCESS Locking OptionsThis section describes situations that might require SAS/ACCESS lock optionsinstead of the standard locking that Teradata provides.3 Use SAS/ACCESS locking options to reduce the isolation level for a read operation.When you lock a table using a READ option, you can lock out both yourself andother users from updating or inserting into the table. Conversely, when other