The entertainment - and particularly television - landscape was undoubtedly ripe for disruption before streaming video became a fact of life. A number of consumer surveys from the last 20 years concur: Americans (in particular) hate their TV subscriptions, and moreover, hate the cable companies that offer them. Across multiple industries, year after year, cable TV and internet providers rank near the bottom of customer satisfaction polls.

Most people know that “cache invalidation” is one of two hard things in computer science (the other one is “naming”) and a strong cache invalidation strategy is as important as your caching strategy. This is because you need to be able to free memory from your storage to make room for new cached content (purging) or you may ban content that should not be cached any more because it is outdated or because it was cached in error and never should have been in cache at all (mistakes happen sometimes).

The verdict is in: Americans are spending increasing amounts of time each day consuming different forms of media - a growing amount of it streaming video. Eleven hours a day, according to Nielsen - yes, you read that right: 11 hours. US adults are consuming media every day in one form or another for about two-thirds of the average adult’s waking hours, for those counting. Similar content consumption patterns hold true for audiences/users everywhere.

VCL is awesome, but it's also a bit frightening to newcomers, and most of the time, people are more interested in something that "just works"™ than "doing the right thing"™ and they google their way out of it.

Problem is that the first thing that sort of works isn't necessarily the right thing, and the proliferation of one particular code snippet is what prompted the writing of this post. The snippet in question? This guy:

sub vcl_deliver {
    if (obj.hits > 0) {
        set resp.http.X-Cache = "HIT";
    } else {
        set resp.http.X-Cache = "MISS";
    }
}

Recognize it? Have it somewhere in your code, maybe? If so, read on, and let's try to do the right thing, and hopefully, get a better setup thanks to it. Don't worry, this is a short one, so hop in.