The hashing structures described in Table 3-1 will give you an idea of just how large Oracle's CBC memory structures can be. For example, the Oracle9i production database contains 1.4 million chains, not 10 chains as shown in Figure 3-5. These are massive memory structures! To reduce the likelihood that a process will be contending for a latch, based on the number of buffers the DBA set, Oracle created 8,192 CBC latches! While this may seem like a lot, each latch must still ensure controlled access to an average of 170 chains.

Table 3-1. Selected Oracle cache buffer chain attributes. All numbers are Oracle defaults, except the chosen block size and the chosen number of block buffers.

You can learn a lot by working through Oracle's general latching algorithm. Even at the highly abstracted view I'll walk you through, the benefit will last your entire DBA career. You will learn how latching appears in Oracle's wait interface, how and if CPU time is accounted for, why latch contention and CPU saturation are so common, and why increasing the instance parameter _spin_count is usually a very bad idea! So let's dig into the algorithm one step at a time.