Figure 6-9 is a small example of an Oracle hashing structure consisting of two CBC latches (CS 800 and CS 810), six CBCs (CBC 00 through CBC05), and eleven buffer headers (BH nnnn). This is a very small example, but it does show all the key pieces with their proper associations. It is common for Oracle CBCs to have a zero length. Oracle does this to help minimize collisions. As I'll describe next, Oracle goes to great lengths to minimize collisions, and only a very unfortunate situation would lead to a buffer chain more than six buffer headers long.

Figure 6-9. A representation of Oracle CBC structure consisting of two CBC latches, six cache buffer chains, and eleven buffer headers. Notice both control structures (CS 800 and CS 810) cover three CBCs, reducing the likelihood of CBC latch contention.

Let's now put this all together and walk through an example. Figure 6-9 will represent the entire CBC structure. In this example, I will make certain abstractions or simplifications, focusing on areas that I have already covered and that are useful for performance firefighting. As you progress through the next chapters, the story will become increasingly detailed, bringing together all that you've learned.