The current LRU chain algorithm is called the touch-count algorithm, which uses a count frequency scheme to place a value on each buffer header. But it has taken Oracle many years to arrive at this algorithm. Understanding Oracle's LRU algorithm progression provides an insight into how the LRU chains work, their shortcomings, and how to ensure they perform as needed.

When the LRU chains become a performance issue, massive LRU chain latch contention will occur. From an Oracle algorithmic perspective, the latching issue is usually the result of server processes holding an LRU chain latch too long while searching for a free buffer. There are many interconnected reasons for this, as well as solution strategies, which I'll cover throughout this section.

When Oracle was first written, the LRU algorithm was extremely simple. Figure 6-16 shows a single LRU chain with the important standard LRU algorithm elements highlighted.