* When the data blocks were then requested (based on the index leaf blocks), they were also requested one at a time from the IO subsystem (think db file sequential read). So once again, these data blocks were placed in the MRU end of the LRU chain. As Oracle systems increased in size, Oracle's buffer cache decreased in usefulness.

At this point, Oracle had big problems brewing. With all the new Oracle features being considered and yet to be considered, Oracle couldn't simply add another clause to handle yet another unfortunate LRU chain situation. It needed a very general, flexible, and high-performing LRU chain algorithm. The Oracle developers found that in the touch-count algorithm.

In a simple, nonassuming patch for Oracle8i Release 8.1.5, Oracle introduced a completely altered LRU chain algorithm that has virtually eliminated all LRU chain latch contention problems. Amazingly, it works without tweaking instance parameters, was slid into the world's largest production Oracle systems without any announcement, and was not documented anywhere in official Oracle documentation. Even scouring Oracle Database 11g documentation, I could find only references to the LRU chain algorithm as a modified LRU.