HTTP: The Definitive Guide

Hit Metering

Origin servers often keep detailed logs for billing purposes. Content providers need to know how often URLs are accessed, advertisers want to know how often their ads are shown, and web authors want to know how popular their content is. Logging works well for tracking these things when clients visit web servers directly.

However, caches stand between clients and servers and prevent many accesses from reaching servers (the very purpose of caches).^[12] Because caches handle many HTTP requests and satisfy them without visiting the origin server, the server has no record that a client accessed its content, creating omissions in log files.

Missing log data makes content providers resort to cache busting for their most important pages. Cache busting refers to a content producer intentionally making certain content uncacheable, so all requests for this content must go to the origin server.^[13] This allows the origin server to log the access. Defeating caching might yield better logs, but it slows down requests and increases load on the origin server and network.

Because proxy caches (and some clients) keep their own logs, if servers could get access to these logs—or at least have a crude way to determine how often their content is served by a proxy cache—cache busting could be avoided. The proposed Hit Metering protocol, an extension to HTTP, suggests a solution to this problem. The Hit Metering protocol requires caches to periodically report cache access statistics to origin ...