Everything you need to know about caching

Caching plugins are hugely popular among our customers, but it’s equally common to misunderstand what they do. We don’t blame you—when it comes to starting a WordPress blog, there’s an insane amount of information out there. Sure, you can find a step-by-step post for anything, but it probably also links to a “Top Ten Plugins for X” post — that never actually explains why you might need to do X in the first place.

Sound familiar? We’ve seen it over and over again: many bloggers read an article about the importance of site loading time, it recommends a few caching plugins, so they click install and move on. Which is fine… until it isn’t. So today, we’re breaking down exactly what caching is, why it’s important to your site, and everything you need to know about caching plugins.

What is caching?

In short, caching means storing bits of information for future use, to speed up delivery. In terms of your WordPress blog, this can happen in two ways:

1. Your browser cache: Every web browser has a cache where it stores a small amount of data for the sites you’ve recently visited. If you visit those sites again, your browser will pull from its cache rather than fetching new data, so it can deliver the site contents faster.

2. Server-level caching and/or caching plugins: Some web hosts offer server-level caching, or you may opt to install a caching plugin. These work similarly on your site. WordPress dynamically generates pages through a coding language called PHP, which queries a database. These caching methods store the output in the cache and deliver those files to site visitors instead, saving the time it takes to run those queries.

Generally, speeding up site delivery to your visitors is exactly what you want. But when you’re actively making updates to your site, particularly to the design of your site, caching isn’t going to show you what’s happening on your site in real time.

Caching and making site updates

The number one thing to remember when making site updates that don’t appear to be working or publishing: if you have caching plugins, or even any performance plugins, start by disabling those FIRST when things don’t work as expected. Even with no caching plugin, you’ll still need to consider your browser cache.

Let’s talk about why.

One of the top files caching plugins AND your browser cache will pick up is your theme’s style.css file, where all of your site design styles are stored. When you make changes, the caching plugin will continue to deliver your old style.css file, and so you won’t see the changes you made. That’s why it’s important to purge your cache in the plugin settings any time you make changes.

Additionally, you probably access your own site a lot, so your browser has saved a fair bit of data for your site in its cache, to speed up loading time. Even if you purge your plugin cache, you’ll still probably need to reset your browser cache. You can force your browser to fetch new data by holding the shift key and clicking the reload button in your browser. Remember, you access your own site more frequently than your readers, so their browser cache will naturally refresh from their normal browsing.

Also, be aware of any performance plugins that you use, particularly for minifying files or serving images. Many of our customers use Autoptimize, which combines all of your styles site-wide into one stylesheet, speeding up delivery. However, since it pulls in styling from plugins as well, you might update a plugin and not see an expected change. You’ll need to reset Autoptimize as well as your caching plugin to see the change. (Side note: Combining all JS files in Autoptimize can break theme and plugin functionality!)

Ultimately, even with purging your cache and resetting your browser cache, you may find changes are still not showing. Sometimes, it just takes time for everything to reset, and you may even need to temporarily deactivate caching and/or performance plugins if you want to check and make sure you did everything correctly.

Caching plugin recommendations

So, do you even NEED a caching plugin?

If your web host has server-side caching, you probably do not need a caching plugin. Caching plugins often conflict with server-side caching, and you’ll need to double-check with your web host before installing any caching plugins. WordPress managed hosts like Flywheel and WPEngine don’t allow caching plugins, as they have their own server-side caching. If you don’t have server-side caching, we recommend the plugin WP Super Cache.

You only need one method of caching on your site, whether that’s server-side caching, or one caching plugin. Do not install and run multiple caching plugins at the same time. Remember how caching plugins work? Once WordPress has dynamically generated a page on your site, the plugin keeps a copy of the static page to serve to your visitors. When you have more than one caching plugin installed, that static page could be generated from WordPress, or it could be a copy from another caching plugin. So let’s say your site goes down temporarily, then one caching plugin picks that up and serves it to the other. Your site’s actually back up, but your caching plugins are telling each other it’s not!

When it comes to performance plugins, just remember that some of these may need to be reset just as your caching plugins do. Similarly, no plugin should perform the same task.

Another thing to watch out for is loading images from a CDN. A CDN, or Content Delivery Network, stores your data on servers in multiple geographic locations and delivers content to the user from the server nearest to them, in order to speed up delivery time. If you serve your images from a CDN, or use the Jetpack plugin to speed up image load times (which is essentially a CDN), any changes you make may not be picked up by your caching plugin, resulting in missing images. You can temporarily turn off your CDN or Jetpack setting to resolve the issue.


We hope that this post was informative and helpful! Are there any other tech issues you want to know more about? Let us know in the comments below!

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