The Oracle® Hacker's Handbook: Hacking and Defending Oracle

1.2. Processes

The processes that make up the Oracle server and services vary depending upon whether you're looking at Oracle on Windows or Oracle on a *nix platform. Recall that a database instance describes all the processes and memory structures that provide access to the database. There are two kinds of processes — background and shadow, or server. Shadow or server processes serve client requests. In other words, when a client connects to the TNS Listener and requests access to database services, the Listener hands them off to a server process. This server process takes SQL queries and executes them on behalf of the client. Background processes exist to support this. There are a number of different background processes each with a different role, including the Database Writer, the Log Writer, the Archiver, the System Monitor, and the Process Monitor, among others.

Suffice it to say that on *nix platforms each of these background processes is a separate running process, as in an operating system process. On Windows, they're all wrapped up into one larger process — namely, oracle.exe. There is a special area of memory that is mapped among all processes on *nix called the System Global Area (SGA). The SGA is implemented as a memory-mapped file (section) and contains information pertaining to the instance and the database. It also contains an area known as the shared pool, which contains structures shared among all users, such as table definitions and the like.

An interesting ...