How to Work with Adaptive Plans
Stelios Charalambides · Apress eBooks · 2017
Imagine you’ve come to conquer the planet SQL but those pesky aliens are constantly changing their bind variable values presenting skewed data all the time, and sometimes not even reporting how many rows there are. The name of the game would be Adapt and Conquer. Another adjective you could use would be Dynamic. Your space fleet’s motto might well be “Victory through Adaptive and Dynamic Plans.” In the world of SQL plans, Adaptive Cursor Sharing has already been introduced in the previous chapter. ACS deals with different combinations of bind variable values and adapts its plan. This allows us to change the plan based on the bind variable values. But what if our plan was so wrong that even during the execution we could see that the ‘wheels were coming off the wagon’? The philosophy, up to 11g has always been to find the best plan and then stick with it. As of 12c and Adaptive Plans the plan can change while executing! This feature ‘Adaptive Plans’ is part of the whole new area ‘Adaptive Query Optimization’. Let’s review the whole area before focusing on Adaptive Plans. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.