We’ve reached the last piece of the architecture puzzle. We’ve investigated the database and the set of physical files that constitute a database. In covering the memory used by Oracle, we’ve looked at one half of an instance. The last remaining architectural issue to cover is the set of processes that constitute the other half of the instance.
Each process in Oracle will perform a particular task or set of tasks, and each will have internal memory (PGA memory) allocated by it to perform its job. An Oracle instance has three broad classes of processes: