During one of my consulting engagements, it was clear that Oracle's memory requirements were exceeding the available capacity. In fact, the situation was so severe that it was impacting response times. When discussing the situation with the operating system administrator, I casually and gently said, "The system clearly has a memory bottleneck." He gave me a confused look and said, "We don't have a memory bottleneck. But there is definitely a lot of memory pressure." So I learned a new term that day to describe a memory bottleneck: memory pressure. It does make sense, and it is a kinder and gentler word, which I always try to use when situations are very tense.

Part of the confusion DBAs face stems from the fact that physical memory is used for a variety of purposes and classified differently. There is real memory, virtual memory, shared memory, nonshared memory, private memory, shared memory segments, code, data, stack, resident memory . . . I'm sure there are other types, names, and categories. The confusion can be significantly eliminated by grouping memory into three categories: real and virtual, shared memory segments, and process-related memory.

The real and virtual memory category is pretty simple. Real memory is the actual memory chips. Virtual memory is not real but provides the appearance of a lot more real memory. Some operating systems manage this better than others, but I digress.