* Influence IMU memory. You can influence an IMU memory increase by increasing the shared pool size or by shifting other objects out of the shared pool. For example, you could set cursor_space_for_time to false and reduce the number of kept shared pool objects. Be careful! Increasing memory could also increase IMU activity, generating even more stress on the latches. Decreasing memory may decrease latch activity, but it is also likely to increase IMU node-collapsing activity, resulting in more traditional undo block activity, which can also result in increased IO. So before you start attempting to influence IMU memory, give it some serious thought, talk with your colleagues, and do some testing.

After reading this chapter, you should have a much better appreciation for the massive technical challenge Oracle undertook and continues to undertake with caching objects of various sizes, duration, and access patterns, and understand their relationships. Of course this complexity has led to a lot of pain for everyone involved: users, performance analysts, Oracle support, and I'm sure the Oracle kernel developers. But as with most pieces of software, if you're serious about improvement and expanding the scope, it can done.

Oracle has made tremendous strides in the shared pool. As a result, for every problem a performance analyst is likely to encounter, there are a number of solutions. In fact, Oracle has taken this so seriously that some of the solutions can be invoked with an alter system or even an alter session command. In the coming years, I suspect we'll see even greater things occur in the shared pool.