As you might expect, the general approach is to increment a counter every time a buffer header is touched. The more popular buffer headers will have a higher touch count and are deemed more popular, and therefore should remain in the buffer cache. While this is generally true, how it is implemented is quite different. Figure 6-18 shows a diagram of the touch-count algorithm.

Figure 6-18. Oracle's touch-count algorithm determines buffer header popularity based on the number of times it is touched. Notice the FTS window concept is no longer necessary and has been removed.

There are three key touch-count algorithm aspects: midpoint insertion, touch count incrementation, and buffer promotion. The following sections look at each of these aspects.