Memoizing pages
This is sharp. Maybe web frameworks (or <cough /> web-centric languages) should provide support for easy memoization.What do ETags do? They allow you, when you fetch a Web resource, to send a short string along with the request saying “this is the signature you sent me for the version I know about”; then the server can look and see if the signature is still good, and if so not bother sending the data redundantly. Which is potentially a big, big win.
But also potentially not. If you look at actual real-world servers that are maxed out, they’re mostly maxing out on computation or back-end database traffic, not on bandwidth to the Net. So the saving that would be really valuable would be if you didn’t have to rebuild the requested page. Unfortunately, both Rails and Django rebuild the requested page, then compute the signature, then check the ETag. Which is extra run-time work in order to conserve a resource (Web bandwidth) that probably isn’t the problem.