May 4, 2015 by Roman Ožana

Server-Side Caching: Speed Up Your WordPress Website


It’s crucial for website response to be as fast as possible, in order to keep the short attention span of today’s website visitors. Slow websites are frustrating for users and often end up deterring them from future visits. In fact, according to a 2009 Akamai study, 57% of users will abandon a page that takes longer than 3 seconds to load.

And since Google considers site speed as a ranking not only for desktop, but mobile pages as well, improving site speed is also great way to get better search engine rankings.

A few months ago, one of our users, Matěj Rokos, noticed that one of his WordPress websites was starting to slow down. He decided to try browser caching to make his WordPress website faster before it had an impact on his system (or users) and tracked the changes using Testomato.

Here were the results:

Leveraging browser caching, he was able to speed up his site by 98.4% from 1.3 seconds to 20 ms.

So, how did Matěj speed up his site? Caching.

Caching is probably one of the most popular topics when it comes to ways you can speed up your WordPress website. In today’s post, we’d like to introduce you to our favorite WordPress caching plugins and show you how Testomato can help you test your website to measure the effect.

Server-Side Caching

WordPress caching is one of the fastest ways to improve site performance. If you’re not familiar with server-side caching in WordPress, there are four different kinds of caching: page caching, database caching, object caching, and opcode caching.

Sourav Kundu has a great guide to explaining different types of WordPress caching on WP Explorer.

It’s definitely worth reading the entire article, but here’s a quick overview:

  • Page Caching: Pages are saved as HTML files in a server’s local storage (hard disk or RAM) and served from the cache (e.g. previously generated data) to your pages when visitors visit your website.
  • Database Caching: While WordPress relies heavily on its database, it’s very inefficient when it makes the same query to retrieve the same data for each page. Database caching saves the results of queries in local storage for faster query result generation.
  • Object Caching: This is an internal API of WordPress for caching complex data queries, which are computationally expensive to regenerate.
  • Opcode Caching: Saves compiled PHP code between requests. PHP files are a list of instructions for the compiler to use and caching speeds up the process generating executable code for the web server to execute.

WordPress Caching Plugins

The following are our favorite caching plugins, but we highly recommend using an installation guide to make sure you set them up correctly. WordPress improvements, if set up incorrectly, can sometimes end up causing more harm than good.

  • WP Super Cache: This plugin generates static HTML files from your website and can refresh them with an interval that you set. This means after a file is generated, your webserver will serve that file instead of processing WordPress PHP scripts.
  • W3 Total Cache: This is the second most popular WordPress caching plugin. It allows a wide-range of caching options and is great for high traffic websites by increasing server performance. Due to its advanced settings, you might want to check out some tutorials like this one before you start messing around with it.
  • Zen Cache (formerly Quick Cache): This page caching plugin takes real-time snapshots to build a cache that can be referenced later to save processing time that could be slowing down your website. It’s very easy to use with a quick 2-minute setup – all you have to do is active the plugin and enable caching.

For more information about using caching plugins and website performance, you can also check out the series about WordPress Optimization on the WordPress Codex.

Benchmarking Your Page Load Speed using Testomato

When you’re preparing to install a caching plugin, you’ll need a way to measure the speed of your website. Using Testomato, we suggest doing an initial test of your page speed.

To do this:

  1. Login to Testomato and open selected project
  2. Click on the Reports tab and scroll down to your Response Timing.
  3. Use your mouse wheel to zoom in or zoom out and check your page response time in milliseconds.

Once you’ve installed your caching plugin, follow the same steps to check the Response Timing graph again to see the difference:

Response time

More Advanced Caching

  • Redis Object Cache: A WordPress object cache that uses Redis for storage.
  • Memcached Object Cache: Use memcached and the PECL memcache extension to provide a backing store for the WordPress object cache.
  • WP File Cache: Basic persistent caching using files (this is not really recommended, but might be a good solution if you’re not able to install another option).

What are our favorite tips for using server-side caching to speed up your WordPress site? We’d love to hear from you! 

Share with us in the comments or on Facebook. You can also find us@testomatocom


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