Monday, February 18, 2008

Benefits of procedures and triggers

Benefits of procedures and triggers
Definitions for procedures and triggers appear in the database, separately from any one database application. This separation provides a number of advantages.

Procedures and triggers standardize actions performed by more than one application program. By coding the action once and storing it in the database for future use, applications need only call the procedure or fire the trigger to achieve the desired result repeatedly. And since changes occur in only one place, all applications using the action automatically acquire the new functionality if the implementation of the action changes.

Procedures and triggers used in a network database server environment can access data in the database without requiring network communication. This means they execute faster and with less impact on network performance than if they had been implemented in an application on one of the client machines.

When you create a procedure or trigger, it is automatically checked for correct syntax, and then stored in the system tables. The first time any application calls or fires a procedure or trigger, it is compiled from the system tables into the server's virtual memory and executed from there. Since one copy of the procedure or trigger remains in memory after the first execution, repeated executions of the same procedure or trigger happen instantly. As well, several applications can use a procedure or trigger concurrently, or one application can use it recursively.
Procedures are less efficient if they contain simple queries and have many arguments. For complex queries, procedures are more efficient.
Procedures and triggers provide security by allowing users limited access to data in tables that they cannot directly examine or modify.

Triggers, for example, execute under the table permissions of the owner of the associated table, but any user with permissions to insert, update or delete rows in the table can fire them. Similarly, procedures (including user-defined functions) execute with permissions of the procedure owner, but any user granted permissions can call them. This means that procedures and triggers can (and usually do) have different permissions than the user ID that invoked them.