A Web Caching Primer

This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by sending an email message to [email protected]. A Web Caching Primer Now a significant part of the Web's infrastructure, Web resource caching can reduce network latencies and bandwidth demands transparently. W hen the Web was new, a single entity could (and did) list and index all of the Web pages available, and searching was just an application of the Unix egrep command over an index of 110,000 documents. 1 Today, even though the larger search engines index billions of documents , any one engine is likely to see only a fraction of the content available. 2 Moreover, with the widespread commer-cialization of the Web, exceeding the " eight-second rule " for downloading a Web page can mean a significant loss of revenue as many users will move on to a new site if they are unsatisfied with the performance of the current one. 3 Finally, as increased Web use necessitates larger and more expensive connections to the Internet, concern for efficient use of those connections similarly increases. This article provides a primer on Web resource caching, one technology used to make the Web scalable. Web caching can reduce bandwidth usage, decrease user-perceived latencies, and reduce Web serv-er loads transparently. As a result, caching has become a significant part of the Web's infrastructure. Caching has even spawned a new industry: content delivery networks, which are also growing at a fantastic rate. Readers familiar with relatively advanced Web caching topics such as the Internet Cache Protocol (ICP), 4 invalida-tion, and interception proxies are not likely to learn much here. Instead, this article is designed for the general audience of Web users. Rather than a how-to guide to caching technology deployment, it is a high-level argument for the value of Web caching to content consumers and producers. The article defines caching, explains how it applies to the Web, and describes when and why it is useful. Though I provide several topical references , readers interested in survey papers should look elsewhere (see the sidebar, " Web Caching Resources " on page 43). Memory architectures use caching to improve computer performance. 5 Because central processing units operate at …