Memory is probably the key to good database performance. Disk I/O is very slow compared to memory access, so the more you can place into memory, the better. The System Global Area (SGA) is the primary area of memory you need to monitor. Since the SGA is the shared memory area used by the instance, the larger you can configure the SGA, the better your performance will be. However, you will have to make tradeoffs between a larger SGA and total available memory. You don’t want to make the SGA so large that you start incurring excessive swapping or paging. Ideally, you want the SGA to remain in memory, and in some operating systems you can pin the SGA into memory. However, you may gain little if the SGA remains in memory and all user processes end up being paged out.

Later in this chapter, we provide SQL scripts you can run over time to watch your system’s memory utilization.