So,  your Web application is running slowly. Does this mean that you need to switch languages or frameworks? Buy (or rent) a larger server, or more servers? Start tinkering with the database calls? Perhaps — but it could be that a smart cache, aka an HTTP accelerator, will help you. Caches and HTTP accelerators are no longer as simple as they once were; they can be clever about static vs. dynamic content.  In this talk, Wim Godden describes ways in which Varnish and other accelerators work, but then describes where such systems are limited, and some advances that nginx has made in this direction.