Oracle Architecture

These notes introduce the Oracle server architecture.  The architecture includes physical components, memory components, processes, and logical structures.

When you fire a SQL from any of the client tools like (SQL Developer/Toad/ SQL PLUS) below processes gets triggered at the back end.

Oracle server:  An Oracle server is divided into an Oracle Instance and an Oracle database.

Oracle instance: Is a means to access an Oracle database. An Oracle Instance divided into two different sets of components.

1.  Background processes (PMON, SMON, RECO, DBW0, LGWR, CKPT and others).
2.  Memory Structures (SGA,PGA).

Oracle database: An Oracle database divided as Physical structures and Logical structures.

Physically database contains
Datafiles
Online redo Logfiles
Controlfile
Archived log files

Logically database is divided into
Tablespace
Segments
Extents
Blocks

Tablespace physically contains one or more datafiles,and logically group of segments.
Segments are group of Extents
Extents are group of blocks.

User and server processes:  The processes shown in the figure are called user and server processes.  

These processes are used to manage the execution of SQL statements.

1. A Shared Server Process can share memory and variable processing for multiple user processes.
2. A Dedicated Server Process manages memory and variables for a single user process.