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Web caching is the process of keeping frequently used pages in memory so that the HTTP server can display them quickly instead of repeatedly processing requests for those URLs. By implementing caching, clients experience faster page retrievals and the load on the web server is greatly reduced. It is one of the most effective ways to scale your application without the need for r-coding or purchasing new hardware.
Oracle Application Server 10 g contains a component called the Web Cache. It is a content-aware service that improves the performance, scalability, and availability of web sites. Application Server Web Cache 10 g uses caching and compression technologies to optimize application performance and more efficiently utilize low-cost, existing hardware resources. Built-in workload management features ensure application reliability and help maintain quality of service under heavy loads. And new in this release, end-user performance monitoring features provide unparalleled insight into end- user service levels. The real power of Application Server Web Cache is its capability to cache both static and dynamically-generated pages.
The Web Cache can be configured to run on its own server or on the middle- tier server (see Figure 1-11). In either configuration, the Web Cache is placed in front of the web server to cache pages and provide content to those browsers that request it. If the Web Cache, acting as a virtual server or virtual request router, can satisfy the request, it will provide content to the client. If the requested content is not cached by the Web Cache or has been marked invalid for any reason, the content is retrieved from the web server and cached in the Web Cache. Application Server Web Cache allows you to define invalidation rules, which can be used to control the amount and types of cached content in your server. Some of the key benefits of Application Server Web Cache can be measured by dramatic improvements in the following areas:
Resource usage Higher throughput and scalability
User experience Faster response times without sacrificing personalization
Availability Intelligent workload management
Productivity No need to roll your own cache means faster time-to-market
Bottom line Reduced infrastructure load translates into cost savings
Intelligence Better visibility into end-user service levels
Some of the key features of Application Server Web Cache include:
Efficient use of low-cost hardware
Fine-grained cache control
Workload management and reliability
End-user experience management
Advanced networking
Single-vendor manageability and integration
Flexible deployments
Figure 1-11: Possible Web Cache topologies
The new features of Application Server Web Cache include enhancements in the following categories:
End-user performance management This is the most significant new Web Cache feature. Administrators can configure Application Server Web Cache to measure end-user response times for individual URLs, sets of URLs, or even entire web-based applications, regardless of whether the URLs are cached. The Analyze functionality lets you view detailed reports in context by group , URL, domain, visitor, or application as well as in a daily, weekly, or monthly context. Further drill- downs provide administrators with response time and load distribution information to help balance web server resources.
Security Web Cache now supports applications that require client-side SSL certificates for PKI-based authentication. Oracle Application Server now supports nCipher s BHAPI-compliant hardware for deployment on servers running Web Cache and/or Oracle HTTP Server.
Caching Previously, administrators could either cache one version of a page for all browsers, or they could cache one version for each browser type and version. Now, administrators can customize the caching rules to define groups of browsers that will share a cached version of a page.
Invalidation The 9.0.4 release of Web Cache introduces an inline invalidation mechanism as an additional means of managing content freshness. Inline invalidation provides a useful way for origin servers to piggyback invalidation messages on transactional responses sent to Web Cache. In previous releases of Web Cache, the URL-based cache key was the unique identifier for a cached document. Invalidation requests needed to specify either exact URLs or a set of URLs and headers matching a regular expression in order to invalidate cached objects. Because it can be difficult for applications to map URLs to the underlying data used to generate those URLs, Web Cache invalidation has been extended in 9.0.4 to support search keys. Cached objects can now be associated with multiple application-specified search keys, with the URL-based key being the primary key.
Compression The Web Cache compression engine now supports self-describing compression policies and more compressible content by compressing documents containing session-encoded URLs, Edge Side Includes (ESI) tags, or the <! “WEBCACHETAG “> and <! “WEBCACHEEND “> tags.
Load balancing and request routing Support for session binding in a cache cluster allows Web Cache to bind a user session to a particular origin web server. This feature is used to consecutively route requests for a unique session to the same origin server, allowing stateful load balancing.
HTTP protocol support Web Cache now supports chunked transfer encoding. HTTP 1.0 (with connection keep- alive ) was used in prior releases of Web Cache, which caused problems for servers that generated dynamic content with unknown content length. Application Servers s support for HTTP 1.1 allows for persistent connection to the Web Cache, even when content length is undetermined.
Usability and manageability Web Cache now includes improved access logging, event logging, and diagnostics, reporting on popular cache misses, integration with Oracle Process Manager and Notification (OPMN), and dynamic configuration for select parameters.
Figure 1-12 shows the administration screen for the Web Cache server. The Web Cache is an administration function, and is therefore only mentioned briefly in this book. The Database Cache, introduced in Oracle9 i Application Server Release 1, has been discontinued.
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