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.

The LRU chain latches are named cache buffers lru chain. The hash chain latches are named cache buffer chains. The names are very close and can lead to quite a bit of confusion. Just remember that the LRU chain latches have lru in their name, and you'll be fine. On pre-Oracle Database 10g systems, the wait event will simply be latch free, so as I presented in Chapter 3, to determine the specific latch, you will need to reference the p2 column in v$session_wait or use the v$latch impact calculation strategy. For Oracle Database 10g and later systems, the wait event will be latch: cache buffers lru chain.