Understanding Plan Instability

You tune a query, it runs well, and then—suddenly—it doesn’t. This is often due to plan instability, where Oracle’s optimizer picks a different execution plan for the same SQL text. Plan changes are normal. But when the new plan performs worse, it becomes a problem.

You should not encounter a plan instability problem. The Oracle Autonomous Database should keep plan instability from becoming a problem. The steps below will help you make a case and submit a ticket if you think you have an instability problem.