The Client Tier Oracle Application Server Tips by Burleson Consulting

At the client level we have either a Java client application or a web browser as the client.  By using a web browser as the client allows the entire application to be located on the server.  The client always gets the latest version when they start the application.  Also the client can use any web browser from any location provided that they can connect to the application server.  The client tier can also consist of an application running on the clients desktop (usually presenting a rich user interface) and connecting directly or through HTTP to the application server.  This requires that the client have the application installed on their desktop.

The Web Tier

At the web server layer we see two important components, the Oracle HTTP Server (OHS) and web cache component (Figure 1.6).  This tier is responsible for managing incoming HTTP requests, caching web messages, and sending XML and HTML back to the client. 

Figure 6: The Oracle9iAS web tier

Let?s take a closer look at these components inside the web tier.

Oracle HTTP Server (OHS)

All Oracle web systems must have enough listener processes so that a single port is not overwhelmed with incoming requests. The Oracle HTTP Server is a component of Oracle9iAS that listens on a specific port and forward J2EE incoming requests thru mod_oc4j to the least-loaded OC4J container. It is imperative that the Web servers have load-balancing intelligence so that a single OC4J container is not overloaded with work.  Oracle has addressed this issue by incorporating the open source Apache product into the Oracle HTTP Server and providing the load balancing capability to the mod_oc4j module.  This makes customization quite easy.

Another huge benefit of the web listener load balancing is that you can customize the Web Cache to load balance multiple Oracle HTTP Servers, thereby adding improved scalability.  When the existing apps servers become overwhelmed, more app servers can be easily added into the architecture.

It is the job of the Web servers to manage the flow of the HTML and XML. On the incoming end, the Web server validates and parses incoming XML strings. For outbound transactions, the Web server takes data from the application server and creates the outbound HTML pages or XML strings. When an incoming transaction requests services, OHS either serves the HTML page or forwards the transaction to an OC4J container where the appropriate component (JSP engine, servlet or Enterprise JavaBean) services the request.

Web Cache

The Oracle9iAS Web Cache significantly enhances performance by reducing the need to regenerate dynamic or static information. The Web Cache is positioned in front of the HTTP server and stores both static and dynamic web content. It has a number of unique features, including partial-page caching, content-aware Web Server load balancing, the ability to cluster web caches so that multiple caches operate as a single logical cache, and the ability to cache content from third party servers such as Sun, IBM , BEA, and others. Internal Oracle tests reveal that adding the Oracle9iAS Web Cache to a three-tier application (client, application server, and database tiers) can reduce the load on the database backend by 95 percent. The Web Cache feature has a dramatic impact on the ability of the application to scale to meet growing e-business demands.

Now, let?s drill-down and examine the central tier, the app server tier.

The App Server Tier

Here we see the core of Oracle9iAS, along with a host of other tools and products. The central components at the App Server tier are the Oracle9iAS instances, and these instances support the Oracle Containers For Java (OC4J)).  The OC4J container host the application?s Enterprise JavaBeans, providing security, naming and connectivity support.  In addition to the Oracle9iAS instances we also see separate components for the following functional areas:

• Oracle Portal ? The component allows for the fast definition and deployment of a dynamically created content based website.

• Oracle Discoverer ? This component allows for the easy end-user query implementation.

• Oracle Form Server ? This component is used to format and deploy and render end-user presentation pages, based on data in an Oracle Database.

• Oracle Personalization ? This component provides personalized URL referrer tracking and a facility for creating customized web pages depending upon the user and their web page viewing history.  The web page history os kept inside Oracle databases in recommendation engine farms.

• Oracle Wireless ? This component allows for wireless communications between Oracle9iAS and wireless devices such as PDAs and cell phones.  Wireless dynamically reformats information to display correctly on the limited screens of most wireless devices.

• Oracle Reports Server ? This component allows for the fast deployment of reports, documents and spreadsheets, all using data from the Oracle database.

• Oracle9iAS Single Sign-On (SSO) - Oracle9iAS has a complete authentication system for identifying users, managing roles, and web services, as well as functionality for Java and portal security.

• Oracle Internet Directory (OID) - This is an LDAP-compliant directory service that provides centralized storage of information about users, applications, and resources in your enterprise.

• Metadata Repository (infrastructure) - This critical component of Oracle9iAS is sometimes referred to as the infrastructure, and it stores Oracle9iAS metadata and allows for a common management interface between multiple instances of Oracle9iAS and the other Oracle9iAS components.

• Oracle Management Server (OMS) - This is a component of the Oracle Enterprise Manager Console, and allows for the managing of the Oracle9iAS instances, databases, and other Oracle9iAS applications.

• Oracle9iAS TopLink ? This is a component with Oracle9iAS that provides object persistence for Java information.  TopLink contain the mapping interfaces to translate the Java structures into relational tables, thereby making Java persistent across independent executions.

Let?s take a look at how these App Server components are partitioned with the Oracle9iAS App Server layer.

This is an excerpt from "Oracle 10g Application Server Administration Handbook" by Don Burleson and John Garmany.