With all this touch count incrementing, resetting to zero, and touch count inquiry, the definition of a popular buffer begins to get a little nebulous. Is a popular buffer one that remains in the cache for 8 hours with an average touch count of 2, or a buffer that remains in the cache for 5 minutes with an average touch count of 250? Well, Oracle has determined a popular buffer simply needs a touch count greater than or equal to 1 (by default) when asked.

Figure 6-21. Shown are touch counts followed by the number of buffers with that touch count (the number of occurrences). Notice that the touch counts are much lower than you may initially think. This is due to the touch counts being reset.

Out of the box and for 99% of all Oracle implementations, Oracle's LRU touch-count algorithm, combined with the default instance parameter settings, enables high-performance LRU chain activity with negligible contention. When the touch-count algorithm does get stressed, it's a unique combination of IO and CPU activity.