Time of enforcement is the phase of query processing during which Adaptive Server applies a given resource limit. Resource limits occur during:
Preexecution – Adaptive Server applies resource limits prior to execution, based on the optimizer’s I/O cost estimate. Use this type of limit to prevent execution of potentially expensive queries. I/O cost is the only resource type that can be limited at preexecution time.
When evaluating the I/O cost of data manipulation language (DML) statements within the clauses of a conditional statement, Adaptive Server individually considers each DML statement. It evaluates all statements, even though only one clause is actually executed.
A preexecution time resource limit can have only a query limit scope; that is, the values of the resources being limited at compile time are computed and monitored only on a query-by-query basis.
Adaptive Server does not enforce preexecution time resource limits statements in a trigger.
Execution – Adaptive Server applies resource limits at runtime, and is usually used to prevent a query from monopolizing server and operating system resources. Execution time limits may use more resources (additional CPU time as well as I/O) than preexecution time limits.
