Downstream caches

So far, this chapter has focused on caching your own data. But another type of caching is relevant to web development, too: caching performed by downstream caches. These are systems that cache pages for users even before the request reaches your website. Here are a few examples of downstream caches:

• Your ISP may cache certain pages, so if you requested a page from http://example.com/, your ISP would send you the page without having to access example.com directly. The maintainers of example.com have no knowledge of this caching; the ISP sits between example.com and your web browser, handling all of the caching transparently.

• Your Django website may sit behind a proxy cache, such as Squid web Proxy Cache (for more information visit http://www.squid-cache.org/), that caches pages for performance. In this case, each request first would be handled by the proxy, and it would be passed to your application only if needed.

• Your web browser caches pages, too. If a web page sends out...