ETA: As of a month later, I’ve actually switched from APC to Zend Optimizer+
Don’t get me wrong, I love caching. I love W3 Total Cache (I’m willing to spend my ‘free time’ testing it, after all), and WP Super Cache saved my life once. So why, on a day where I got a 400-600% uptick in traffic (not a joke), did I turn all my caching off? I’m daring, and a little crazy, but I wanted to see if it could be done. I would not have tried this if I was on a smaller server: if you’re getting as much traffic as I am, and you’re on shared hosting, you really need to move to a VPS or Dedicated Server if you want to turn off caching via plugins. It’s not to say that caching is better or worse than not-caching, or vice versa, or that one is a rich-man/poor-man equivalent of the other. Caching plugins are an inexpensive way to speed up your site, and if you can’t afford a bigger server they will buy you the time you need to figure out a better solution. Even with a good plugin and setup, if you get hammered with a lot of traffic, you will crash your site unless the server’s optimized too. Again, what I’ve done is not something I’d try on a low-end server with high traffic.
When I started measuring the effectiveness of all this, I used:
- GT Metrix (tests Yslow and Google Page Speed at once)
- Apache HTTP server benchmarking tool
To understand what caching is and why we use it, it’s good to understand the basic concepts, and to start by looking at what caching plugins are, how they work, and where their pitfalls are.
- You want the user to only download what’s changed.
That sounds easy, but WordPress isn’t static HTML, it’s PHP, and that means every time you visit the page, it runs various proceses to give you the latest and greatest files. The problem with this dynamic code is where content changes rapidly (think ‘comments’ or ‘forums’ or ‘BuddyPress Groups’). Suddenly caching ‘pages’ as wholesale chunks of html doesn’t help if you have to re-cache when someone leaves a remark. Add in the possibility of 4 or 5 people commenting at once, for 12 hours, and now you’re risking a thrashing situation where you keep trying to cache, but it keeps flushing. This is why most people use plugins that handle things elegantly, or try to, where the ‘static’ part of the page (sidebar, etc) are HTMLized, but the dynamic part is left alone. This helps when you have a portion of every page is dynamic, like a shopping cart with a ‘Your order…’ box.
But the downside is that you have to write fancy code that remains dynamic portions, and while it certainly can be done, it’s not fun, and let’s be honest, a theme developer doesn’t know which cache you’re going to use, so how can it write the right way for that? The only way to make a truly dynamic and cachable site is to do it from day one, with your theme, server, and plugins all crafted to provide the best experience. And then we have reality, which is we start with something simple, wake up to something large, and experience growing pains.
Accepting the fact that we’re not starting from nothing, that we have an existing site with content and activity, the first thing most people do is install a plugin. Now, back to what I said before, this isn’t a bad thing. It’s a good first step and will buy you time. It’ll also show you where you need to go. If you don’t have server root access, this may be a your limit, too, as some of the other things I like to do to speed things up without a cache will require it (or you’ll have to ask your hosts and they may tell you to upgrade).
If you’re going to use a plugin, WP Super Cache (WPSC) and W3 Total Cache (W3TC) are the best two. W3TC is way more advanced, and has a lot of extra bells and whistles, but personally I find that once you can master it, you’re well on your way. Remember though, you’re sacrificing a lot of control here by using a plugin. They’re going to, by their nature, cache everything they can, and we’re back to where we were with the dynamic site generation issue. W3TC has a bunch of extra .htaccess/nginx rules which parse data before you hit WordPress. WPSC can do that, or use PHP (which is slower).
The dynamic nature of my site is what drove me away from caching plugins. I use other CMS tools, and for my infrequently updated Wiki and ZenPhoto Gallery, where content is very much static, caching makes perfect sense. But when I want to run a simple community site with WordPress, I have to consider all aspects of user experience. Speed is hugely important, but so is the user getting the content they want. Stale content is a killer.
The reason I decided to see if my site ran slower without caching was that I was reinstalling caching and I thought “This is a perfect time to benchmark.” When I did I was astounded. There was very little difference in a benchmark test. Really no difference between at all, since it was within the results of each other, but I neglected to save the results at the time. I did however snap a picture of my server load(The unrelated part is where I was uploading 10megs of media. Unrelated.):
Browser Caching is the first thing to tweak, as that tells browsers to cache content. The way this works is your .htaccess tacks on extra information while content like images and CSS are being downloaded, to say “This content is good for X days.” With WordPress, you don’t have to worry about changing the CSS, as most themes and plugins are extra smart, in that they append a version to the end of your CSS like this:
style.css?ver=1.9.1 That 1.9.1 is the version of Genesis I’m running, so when that changes, the version changes, and browsers see it as a new file and re-download. That’s pretty cool. (I do wish that child themes pulled in their version, so you could increment that way.) We still have to tell the broswers to cache, and for how long, so near the top of my .htaccess (just below my hotlink protection) I have this:
## BEGIN EXPIRES ##
I’ve added in only the types used by my site. I used to use Pragma caching headers as well, but I noticed that Google PageSpeed Insights and YSlow ignore them. Turns out that Pragma headers aren’t honored all the time, in fact, they aren’t honored often, so I just removed them. I don’t think it slowed my site down to have them, but the less to maintain, the better. This had an immediate positive impact, so it was time to look at the server.
Over the years, I’ve tuned httpd.conf so it doesn’t crash, I’ve got CSF locked down to prevent people from DoS’ing me over TimThumb, and I of course have APC turned on. Recently I broke down and installed mod_pagespeed when I upgraded to PHP 5.4. Just those things have done a lot to make my site run faster. I intentionally skipped things like Varnish or TrafficServer, as well as a CND or Google’s PageSpeed Service. I (still) don’t need them.
I added in a couple more to my standard: remove_comments and rewrite_images. Then I went back to my site’s .htaccess and started turning on the things I wanted per-site.
The ones I picked are:
Putting those in my .htaccess looks like this (note: no spaces between the filter names, or it all blows an error 500):
That also means I don’t have to use a plugin to use Google Analytics for my whole site! This may not mean a lot to you, but I have multiple ‘apps’ on my site (four now) and when I edit themes, if I don’t have to do anything, it’s easier. Google will tell you not to do this, but unless they have a way for me to set pagespeed.conf in the /home/user/ folder of my server, I don’t know another per-user way about this.
Finally I went back on my word, and I installed a plugin. APC by Mark Jaquith. This isn’t a full reversal on my ‘No Plugins!’ stance before, though. All APC is, you see, is but one file that sites in wp-content and kicks things over to APC. Doing this alone moved my TTFB from an F to a B. Which is pretty impressive. Giving it a little time to bake, this worked out okay.