Oracle7 Server Tuning
The Optimizer
When a SQL SELECT, UPDATE, INSERT, or DELETE statement is processed, Oracle must access the data referenced by the statement. The optimizer portion of Oracle is used to determine an efficient path to referenced data so that minimal I/O and processing time is required for statement execution. The optimizer formulates execution plans and chooses the most efficient plan before executing a statement. The optimizer uses one of two techniques to formulate execution plans for a SQL statement: a rule-based approach or a cost-based approach. Each of these approaches is described in Chapter 5, "The Optimizer".