Interestingly, Oracle does not have to respect your subpool number wishes. In fact, in the example shown in Figure 7-13, the instance parameter was set to 2 and the instance restarted, yet Oracle created three subpools. And without the instance parameter manually set, Oracle created only a single subpool. So while you can influence Oracle, it still reserves the right to make changes.

Figure 7-13. Shown is the OSM script, spspinfo.sql, which shows basic information about the number and size of the shared pool subpools. In this example, three subpools exist.

Memory allocation is fairly straightforward. It follows a standard LRU algorithm combined with pinning and locking. When an Oracle process (server or background) requests memory, a portion of the Oracle's kernel called the heap manager is executed. While the details continue to change, the conceptual algorithm is pretty much the same.