Oracle Core

The Core of an Oracle Database

There are three major structures on an Oracle Database server:

• Storage Structures.
• Memory Structures.
• Process Structures.

A basic system of Oracle databases consists of a database and a database instance.

The database (physical storage)

It consists of two independent physical and logical structures. Because they are independent, the physical storage of data can be managed without affecting access to logical storage structures.

The instance (memory and processes)

It consists of memory structures and background processes. Each time an instance is started, a shared memory area called the global system area (SGA) is mapped and the background processes are started. After starting an instance, it is associated with a specific database. This is called database assembly. The database is then ready to be opened and thus accessible to authorized users.

Private Memory Zone

The PGA (Program Global Area) is the private memory zone of each Oracle process, where the information it contains is basically about the session (which user is connected, privileges, cursors are open, ordering buffer).