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.

Suppose you are a server process executing a SQL statement. Based on the SQL statement and Oracle's data dictionary, you discover there is row you must access located in file number 35 with a block number of 2435.

You hash 35,2435, which hashes to CBC 02. If the hash function and the number of buckets have not been changed, hashing this block will always point to CBC 02. So, if the block does exist in the buffer cache, it absolutely must reside in CBC 02. Referencing the CBC, you realize that you must acquire latch CS 800 in shared mode. You go through the spinning and sleeping algorithm, burning CPU and sleeping (screaming "latch free cache buffer chain!"), but finally do acquire latch CS 800.