Execution Plan Optimization and Consistency

Abstract

When you issue a SQL statement, the query optimizer creates an execution plan that describes the combination of steps Oracle takes to retrieve or modify the data. For example when you submit a query, the optimizer quickly produces several execution plans and will determine which plan is most efficient. In most scenarios, the prior behavior results in adequate-performing execution plan. However, you will encounter situations where query performance is poor and you need to understand the optimizer’s choice of an execution plan. Listed next are features you can use to guide the decision path the optimizer uses when selecting an execution plan: