Oracle9iAS Architectural Overview
Oracle Application Server Tips by Burleson
Beginning with the Oracle Web server product
in the 1990s, Oracle has continuously improved and streamlined its
products into a comprehensive solution for Web based applications.
Oracle9iAS is the latest incarnation in a
long evolution of Oracle application products. Starting in the
mid 1990?s with Oracle WebServer and Oracle Application Server
(OAS), Oracle9iAS has evolved into an extremely sophisticated system
of inter-related modules, all of which can be configured according
to your specifications. There are two ways to view Oracle9iAS,
one from a functional level and another from an architectural level.
Let?s begin with an architectural overview of Oracle9iAS.
The Oracle9iAS Multi-tiered Model
As Oracle products evolved into a
multi-tiered architecture, we started to see Oracle products reside
at several ?tiers? or hardware levels. These tiers are layers
that represent hardware layers, with each tier being comprised of
one or more servers. (Figure 1.1). Because of the flexibility
of Oracle9iAS, Oracle shops can adopt a two-tiered, three-tiered, or
four-tiered model. As a general rule, the larger system will
have more levels and more servers at each level.
Figure 1: Oracle application tiers and
Oracle component products
At each one of these layers we see important
The Client tier ? This is comprised of the
web browsers for the end-users.
The Web Tier - The web-tier comprises the
Oracle HTTP Server and the web cache.
The App Server tier ? This comprises the
core Oracle9iAS, plus ancillary products such as Oracle Portal,
Oracle Developer, Oracle Reports and Oracle Forms Server.
The Database Tier ? This is the layer that
is the core Oracle database. It may be a single instance, or
many instances defined to a RAC cluster.
It?s important to note that not all shops
will use all four tiers. For smaller shops, it is common to
combine multi tiers into the same level. The choice of the
number of tiers is directly related to the size of the Oracle9i
implementation and the number of servers that are dedicated to the
For small shops, it is common to see a
two-tier to data model (Figure 1.2). Here we see the client
tier consisting of all of the external PC clients and a combination
of the Web server tier, the App Server tier, and the database tier,
all running on a large single server, usually with lots of RAM and
multiple CPUs. The benefit of this approach is the shared
server resources because the single server will be able to supply
additional CPU and RAM processing according to the specific demands
of each of the Oracle9iAS components. The downside of the
two-tiered architecture is the limited flexibility. This is
because it is not easy to add additional hardware resources on
Figure 2: The Oracle9iAS architecture for a
In medium-sized shops, the three tier data
model predominates (figure 1.2) In the three tier model, we
see the client tier, followed by the separation of the Web Server
tier and App Server on separate server. The database tier is
also separated onto a different server, thereby providing isolated
data resources for the Oracle database. The benefits of the
three tier data model are that increases in processing demands
either at the database or the App Server level will not affect the
performance of the other components within the Oracle9iAS
architecture. Another benefit is that additional Oracle9iAS
instances can be created, and additional Oracle SGA regions can be
easily added when processing demands warrant an increase.
Figure 3: The Oracle9iAS architecture for a
Now that we see the components of each tier,
let?s examine how these tiers look when used in a large eCommerce
The hardware architecture of Oracle9iAS
In Figure 1.4 we see that we can have
multiple instances of the components at each tier. In this
example we see that we have two sets of Oracle HTTP Servers (OHS),
each listening on a different port for incoming database requests.
As requests enter the system OHS passes the request to the
least-loaded Oracle9iAS instance on the app server tier.
Figure 4: Oracle9iAS tiers and instances
At the app server tier we see multiple
instances of Oracle9iAS, and we may also see multiple instances of
the Oracle Forms server, Oracle Developer and Oracle Reports.
These multiple instances are normally on separate servers, and this
provides the Oracle9iAS administrator with the ability to create an
infinitely scalable architecture. Whenever any components at
any tier becomes overwhelmed, and Oracle9iAS administrator can
create a new instance on a new server, and add the instance into the
Oracle9iAS architecture using Oracle Universal Installer and
maintained using the Enterprise Manager.
The Oracle9iAS instances will connect to the
database tier. For very large systems, Oracle9i Real
Application Clusters (RAC) provides the ability to have multiple
instances of the database, all mapping to a single database.
Using the same technique as the other tiers, whenever the existing
instances become overloaded, another Oracle9iAS instance can be
created on a new server, and the server can be added into the
This ability to scale by adding new
instances and server is a critical aspect of Oracle9iAS
administration because it is the single most important tool for
ensuring that the system always has adequate hardware resources.
The Functional Architecture of Oracle9iAS
Now let?s look at the same architecture from a functional
perspective (Figure 1.5). Here we wee the functions of the
instances at each level, and this should give you an idea about how
the multi-tiered architecture is used to isolate the logical
components of the application.
Figure 5: Oracle9iAS functional tiers
At the web tier we see that the main
functions are the listener, which listens on a specific port for
incoming requests, and web cache components that stores web page
components, and the load balancing mechanism for ensuring optimal
allocation of computing resources to the app server tier. The web
tier is managed by the Oracle HTTP Server which is based on the
Apache web server.
The app server tier controls all of the
business logic and content assembly. Components such as Oracle
Portal are used to define web page components, Oracle reports
defines content specifications, and Oracle single-sign-on (SSO)
controls security for the app server layer. At the database tier we
see the standard Oracle data management functions for the storage
and retrieval of application data. All the components running on
the application tier have the ability to connect to and retrieve
data from the database using any of the available J2EE database
connection methods. These are discussed in detail in later
chapters. However, Oracle9iAS may have its own database if you
install the Oracle9iAS infrastructure. With infrastructure an
Oracle database instance called iasdb manages Oracle9iAS components,
security and preserves Oracle9iAS usage data.
Now that we understand the Oracle9iAS
architecture at a high level, let?s take a closer look at each of
these tiers and see how they interact with each other.
This is an excerpt from "Oracle
10g Application Server Administration Handbook" by Don Burleson
and John Garmany.