Databases Reference
In-Depth Information
Figure 3-2. Accessing a database
Oracle Net and Establishing Network Connections
The server processes shown in
Figure 3-2
are connected to the client processes using
some kind of network. How do client processes get connected to Oracle server
processes?
The matchmaker that arranges marriages between Oracle clients and server processes
is called the Oracle Net Listener. The Listener “listens” for incoming connection requests
for one or more instances. The Listener is not part of the Oracle instance—it directs
connection requests to the instance. The Listener is started and stopped independently
of the instance. If the Listener is down and the instance is up, clients accessing the
database over a network cannot find the instance because there is no Listener to guide
them. If the Listener is up and the instance is down, there is nowhere to send clients.
The Listener's function is relatively simple:
1. The client contacts the Listener over the network.
2. The Listener detects an incoming request and introduces the requesting client to
an Oracle server process.
3. The Listener introduces the server to the client by letting each know the other's
network address.
4. The Listener steps out of the way and lets the client and server process communicate
directly.
