This will be our starting point for CPU subsystem performance analysis. The rest of this section will build from this point.

Have you ever heard someone say the IO subsystem needs to be balanced? Of course you have, because an IO subsystem can have very active devices and not very active devices. But as a DBA, it's very unlikely you have heard someone say the CPU subsystem needs to be balanced. That is because any available CPU core can service any transaction in the queue. Unlike an IO subsystem, where reading and writing must occur at an exact spot on a physical spindle, any CPU core can process any waiting transaction. This has massive implications.

Figure 4-2 shows a four-CPU core subsystem in three different situations. Situation A is very busy CPU subsystem with two processes waiting in the queue. Situation B looks like a very idle CPU subsystem with only one active transaction. However, situation B could also represent a problem. If the transaction being serviced in situation B is a relatively long transaction, why are the other CPUs not participating, but instead standing idle? This is a scalability issue, and as mentioned in Chapter 3's discussion of serialization, everyone-from the businesspeople to the operating system vendors-gets involved, so this situation never occurs.