Databases Reference
In-Depth Information
Client process
The client process can run on the same machine as the instance or on a separate com‐
puter. A network connects the two computers and provides a way for the two processes
to talk to each other. In either case, the concept is essentially the same—two processes
are involved in the interaction between a client and the database. When both processes
are on the same machine, Oracle uses local communications via Inter Process Com‐
munication (IPC); when the client is on one machine and the database server is on
another, Oracle uses Oracle Net over the network to communicate between the two
machines.
Application Servers and Web Servers As Clients
Although the discussion in the previous section used the terms
client
and
server
exten‐
sively, please don't assume that Oracle is strictly a client/server database. Oracle was one
of the early pioneers of client/server computing based on the notion of two tasks: a client
and a server. But when you consider multitier computing involving web and application
servers, the notion of a client changes somewhat. The “client” process becomes the
middle tier, or application server.
You can logically consider any process that connects to an Oracle instance a client in
the sense that it is served by the database. Don't confuse this usage of the term client
with the actual client in a multitier configuration. The eventual client in a multitier
model is some type of program providing a user interface—for example, a browser
running an application composed of HTML and Javascript.
The Oracle WebLogic Server application server, which is part of the overall Oracle plat‐
form, is designed to act as this middle tier. WebLogic Server works seamlessly with the
Oracle Database.
Figure 3-2
illustrates users connecting to an Oracle instance to access a database in both
two-tier and three-tier configurations, involving local and network communication.
This figure highlights the server process connection models as opposed to the interac‐
tion of the background processes. There is a traditional two-tier client/server connec‐
tion on the left side, a three-tier connection with an application server on the right side,
and a local client connection in the middle of the figure. The two-tier and three-tier
connections use a network to communicate with the database, while the local client uses
local IPC.
