On Caching

A flurry of new visitors from Tam’s (hi everyone, welcome!) got me thinking a bit about the performance of this site. Combined with not much going on with gun-related topics here in Switzerland, I figured I’d write a bit about tech.
This site runs WordPress on a S-sized Simple Hosting instance at Gandi‘s Baltimore facility. As a sort of hybrid of shared hosting and a VPS, it has a surprising amount of “oomph”: it has dedicated Apache, PHP, and MySQL processes, uses APC to cache PHP opcodes, and sits behind a series of load-balanced Varnish cache servers which cache static content. It’d make sense to take advantage of those resources to ensure things are speedy.
Out-of-the-box, WordPress dynamically generates each page entirely from scratch: this involves about a hundred database calls and a bunch of PHP work. Considering that content here changes relatively infrequently (yeah, I should write more), it doesn’t make sense to generate each page anew for each visitor since this takes a fair bit of resources.
That’s why I use Lite Cache to cache static content: the first time a visitor requests a page, it’s dynamically generated and sent to them as normal, but the now-generated page is saved on the server in the cache. If a second visitor requests that same page, the cached version is sent to them; since this is just a static file that doesn’t need to be generated from scratch, the server can send it right away, so it loads faster for the visitor. In addition, the static file is stored on the Varnish caches, which are specifically designed for high-performance caching. If the content ever changes (e.g. I make a new post, someone leaves a comment, etc.), the cached version is updated to reflect those changes.
Combined with the front-end Varnish caches, this can swiftly serve up content to large numbers of users — I’ve load-tested it with over 1,000x the typical daily traffic and it doesn’t break a sweat.
That’s cool and all, but why bring it up now?
Because I forgot a critical detail: I only tested it with desktop browsers, where it worked great. However, once someone hit the site with a mobile browser (perhaps on their smartphone or tablet), things went wonky: the site correctly detected that the site was using a mobile browser and generated a mobile-friendly version, which the cache dutifully stored for other visitors. Unfortunately, the cache wasn’t smart enough to tell that all the other readers were not using mobile devices, and started serving up the mobile version to desktop browsers. Whoops.
I’ll make a note to test for this sort of stuff in the future.
Since mobile users make up a tiny fraction of the already-small number of readers here, I’ve disabled the mobile-friendly theme until I can get things sorted out.
Since this is nominally a gun blog, I suppose I should try to connect this situation to guns in some way. Here goes: don’t assume everything will always work the way you think it will. Train for a variety of situations. If your training consists only of calmly standing upright in a well-lit range shooting at stationary targets with a full-sized pistol, you’re not well-prepared for a situation when, for example, a bad guy mugs you with a knife outside your office when all you have is a Beretta Jetfire and a cup of coffee. It definitely doesn’t prepare you for things that go thump in the night.Whether you’re adjusting web caches, training at the range, or sending a rocket to the moon, it’s wise to keep in mind that the universe has a perverse sense of humor.

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