Web Caching

Dynamic Web Pages

Many people worry that caches do not properly deal with what they call “dynamic pages.” Such pages are considered dynamic because the content might be different for every request. Time-sensitive information, such as stock prices and weather reports, logically fall into the category of dynamic pages. Pages that have been customized for the user, to include his name or targeted advertisements, are dynamic as well.

Historically, dynamic pages have been problematic because some web caching software had relatively aggressive caching and refresh policies. Dynamic pages were cached and returned as cache hits when perhaps they should not have been. Part of the blame lies with the early descriptions and implementations of HTTP. The HTTP/1.0 RFC [Berners-Lee, Fielding and Frystyk, 1996] was not published until May of 1996, while active development on web caching had been ongoing since early 1994. Without a stable protocol description, implementors are certainly prone to make some mistakes. Even when HTTP/1.0 became official, it still lacked a good description of what can and cannot be cached. Section 1.3 of RFC 1945 states:

Some HTTP/1.0 applications use heuristics to describe what is or is not a “cachable” response, but these rules are not standardized.

Some of the blame lies with the origin servers, however. Even though HTTP/1.1 has more caching features than HTTP/1.0, the older protocol does have enough functionality to prevent a compliant proxy from returning hits on ...