Introduction

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Server-side caching techniques have long been used to improve Internet performance of Web applications. In general, caching improves response time and reduces system load. Most techniques cache static content, which is data that changes rarely, if at all, such as graphic and many text files. While the solutions for caching static content have resulted in excellent performance for some Web sites, they have little or no value in enhancing the performance of Web sites with dynamically generated pages. Dynamic content is the data that changes over time (such as stock prices, sport scores, and weather forecasts) or is personalized (such as shopping carts). Dynamic content can also be cached.

For years, IBM Research has developed and refined technologies that enable the caching of dynamic content. These technologies were implemented, deployed, and verified at various high-volume sport event sites such as the Olympics [1,2]. The success of the sport sites [3] demonstrated the feasibility and significance of caching dynamic content [4,5], and confirmed the scalability and reliability of the caching technologies. Based on these proven and scalable caching technologies, IBM developed a dynamic content caching solution for Java 2 Enterprise Edition (J2EE) applications running on WebSphere Application Server Version 5.0.

WebSphere Application Server offers a built-in dynamic cache service for serving dynamic content and caching data. There is no time-consuming installation and integration work needed to activate the dynamic cache service. The cache is enabled /disabled declaratively using simple XML configuration files or using the WebSphere Application Server's Administrative User Interface; these methods not only allow caching to be brought up quickly and easily, but also provide great flexibility and control at runtime. Also, you can define your existing caches, such as the caching component of WebSphere Edge Server or IBM HTTP Server, as external caches and use them in conjunction with WebSphere's dynamic cache service.

This chapter introduces the presentation level caching features of the WebSphere Application Server dynamic cache service. These features are:

• Servlet/JSP Result Cache, which is nonintrusive, effortless, and ready to cache any existing whole page or fragment generated by a servlet or Java Servlet Page™ (JSP).

• Command Cache, which is used to cache dynamic data that is "expensive to re-create." This data requires either back-end requests, such as back-end Java database connectivity (JDBC) calls, or additional CPU intensive computation/manipulation at a later time.

• Replication Support, which enables cache sharing and replication among multiple servers and tiers (Figure 5-3).

• Invalidation Support, which includes rule-based, time-based, group-based, and programmatic cache invalidation techniques to ensure the freshness, consistency, and accuracy of the content.

• Edge of Network Caching Support, which extends the WebSphere Application Server caches into network-based caches, through the implementation of external cache control and distributed fragment caching and assembly support.

• Tools, which assist in configuring the cache and monitoring runtime

More information on additional features of WebSphere Application Server, such as EJB caching and Web Service caching, can be found at the WebSphere Application Server V5 InfoCenter [7].

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