Database Instance

Database Instance

Database Architecture Deepak Kharb   May 14, 2019

A database instance contains a collection of memory structures and Oracle Database background processes.

• The main memory structures are the System Global Area (SGA) and the Program Global Areas (PGAs).
• The background processes operate on the stored data (data files) in the database and use the memory structures to do their work.

A database instance exists only in memory.

Oracle Database also creates server processes to handle the connections to the database on behalf of client programs, and to perform the work for the client programs.

For example, parsing and running SQL statements, and retrieving and returning results to the client programs.

These types of server processes are also referred to as foreground processes.

Oracle Database Server

Oracle Database Server

Database Architecture Deepak Kharb   May 10, 2019

An Oracle Database consists of at least one database instance and one database.

• The database instance handles memory and processes.
• The database consists of physical files called data files and several database system files.

The listener is a database server process. It receives client requests, establishes a connection to the database instance, and then hands over the client connection to the server process.