Process Architecture

A process is a mechanism at the operating system level whose purpose is to run a series of steps. Some operating systems use the terms task, job, or thread, but regardless of the name, they all perform a job through designated steps. Each process usually runs in its own memory area.

Oracle instances have two primary types of processes: user processes and Oracle processes. The following list describes these and other processes:

• User processes These are created and maintained for the sole purpose of facilitating the running the software code of an application program or an Oracle tool (such as SQL*Plus or Oracle Enterprise Manager). User processes manage the communication with the server processes through the program interface but do not interact directly with the database.

• Oracle processes These are invoked by other processes to perform the functions on behalf of the calling process. Several different Oracle processes are discussed in the following section.

• Server processes Oracle creates these to handle requests from the connected user processes; it directly interacts with the Oracle Server. The server processes communicate with the user processes and interact with Oracle to carry out the requests made by the user processes. It can be shared or dedicated.

• Dedicated server process The typical way that the user processes connect with the server processes in the instance is through a dedicated server process, or a one-to-one relationship between the user process and the server process.

• Shared server process These processes have a many-to-one relationship between the user processes and the server processes that connect via a dispatcher.

The differences between shared server architecture and dedicated server architecture are covered in depth for the Performance Tuning exam.

Now let's look at those processes that Oracle manages on its own, the Oracle background processes.