When you finally get the block from disk, you again issue a gettimeofday call, calculate the time difference, and record that into Oracle's wait interface structures for anyone to see via wait event views. Now with the block in hand, you still cannot peek inside, as it must first be appropriately placed in the buffer cache and all the relevant memory structures must be appropriately changed. How this is performed is what much of the rest of this chapter is about.

One of the best (and most interesting) ways to learn how to solve performance problems is to devise ways to create the problem! Referring to Figure 6-9, there are three classic ways to slow CBC performance:

* If we decrease the number of CBCs (for example, remove CBC 04 in Figure 6-9), the average chain length will grow, increasing concurrency on the remaining chains and also increasing CBC scan time.