HTTP: The Definitive Guide

Caches and Advertising

If you’ve made it this far, you’ve realized that caches improve performance and reduce traffic. You know caches can help users and give them a better experience, and you know caches can help network operators reduce their traffic.

The Advertiser’s Dilemma

You might also expect content providers to like caches. After all, if caches were everywhere, content providers wouldn’t have to buy big multiprocessor web servers to keep up with demand—and they wouldn’t have to pay steep network service charges to feed the same data to their viewers over and over again. And better yet, caches make the flashy articles and advertisements show up even faster and look even better on the viewer’s screens, encouraging them to consume more content and see more advertisements. And that’s just what content providers want! More eyeballs and more advertisements!

But that’s the rub. Many content providers are paid through advertising—in particular, they get paid every time an advertisement is shown to a user (maybe just a fraction of a penny or two, but they add up if you show a million ads a day!). And that’s the problem with caches—they can hide the real access counts from the origin server. If caching was perfect, an origin server might not receive any HTTP accesses at all, because they would be absorbed by Internet caches. But, if you are paid on access counts, you won’t be celebrating.

The Publisher’s Response

Today, advertisers use all sorts of “cache-busting” techniques to ensure ...