Oracle server
An Oracle server, a database management system, consists of an Oracle instance and an Oracle database.
The instance and the database together constitute an Oracle server.
The architecture of Oracle Server can be described in three phases:
User login to the database
Memory structures that are part of the Oracle instance
Background processes that are part of the Oracle instance
Physical structures of files forming the Oracle database.
User login to the database
Two processes allow a user to interact with the instance and ultimately with the database: the user process and the server process.
Each time a user runs an application, such as an application for human resources management, financial management, or just an SQL command, the client machine first launches a user process to establish a connection from the user to the Oracle instance.
The Oracle Listener Listening Process
The Oracle listener process is the primary server-side Oracle component that establishes the connection between client computers and an Oracle database. The listener can be seen as a big ear that listens for connection requests to Oracle services.
Theoretically, a server machine can host several Oracle databases and one listener and only one to allow a client to connect to the Oracle instance of his choice. The instance name is submitted by the client during the connection process (step 1).
Two cases are possible:
A Listener process can serve multiple databases configured on the same server machine,
Several listener can be configured on the same machine (for failover or load balancing purposes to support heavy loads of connection requests).
In a dedicated server configuration, the Listener starts a new server process for each client and gives it control of the client session. Each client connection is served by its own server process.
The diagram above corresponds to a dedicated server configuration and for a client / server application.
The connection process goes through the following steps:
The customer contacts the Oracle listener by choosing the instance to which he wishes to connect (request for a service name).
The listener starts a dedicated process called a server process
The listener sends an acknowledgment to the client with the address of the dedicated server process
The client establishes a connection with the dedicated server process
The server process connects to the Oracle instance on behalf of the user process (creation of a user session)
It is the server process that connects to the Oracle instance to serve the user process throughout the client session.
The user process does not directly interact with the Oracle server. Rather, it is the server process that interacts with the Oracle server, responds to user requests and returns results to the user.
To learn more about the components and basic concepts of the Oracle architecture, take look at our Expert DBA Team Club blog and more advance topics are available at this source.
