Hummingbird Cache for WordPress Performance Review

The Hummingbird Cache plugin is one of many different caching plugins available in the WordPress ecosystem. Enabling it will increase your site’s performance significantly, but by how much? In this review we’re going to use Kernl’s WordPress Load Testing tool to push our Hummingbird Cache WordPress installation to it’s limits.

HummingBird cache pushed to limits

Test System Setup

As with most of our cache reviews, we used a pretty standard PHP-FPM + Nginx setup.

  • DigitalOcean $5/month 1vCPU 1GB RAM machine
  • Ubuntu 20.04
  • PHP (FPM) 7.4
  • Nginx 1.18
  • MariaDB 10.3
  • Content – For this test I imported the contents of my personal blog and used it for testing.

The test system was located in San Francisco, CA, USA. Load test virtual users were located in New York, NY, USA along with some of the high volume tests spreading virtual users around Europe.

How did we test Hummingbird Cache?

To test the Hummingbird WordPress caching plugin ran 3 different load tests with Kernl WordPress Load Testing.

  1. Baseline – This is a 200 concurrent user test for 60 minutes with no caching enabled.
  2. Cache Enabled – The same test as the baseline run, but with caching enabled. This is the “apples to apples” comparison.
  3. Cache++ – After the “apples to apples” comparison, we pumped up the concurrent users to 400 to see how well the plugin would respond.

Baseline Load Test

The baseline load test is just the bare WordPress setup with no plugins enabled and the base TwentyTwenty theme. As expected performance isn’t great but it isn’t terrible either.

Hummingbird Cache - Baseline Request Throughput
Hummingbird Cache – Baseline Request Throughput

You can see from the throughput chart that the base WordPress installation with no caching enabled settled in at around 34 requests/s. Not too shabby, but what was the quality of those requests?

Hummingbird Cache - Baseline Response Times
Hummingbird Cache – Baseline Response Times

The average and median response times tell a story steady degradation of the user experience before finally settling at just shy of 5 seconds. If I were a reader of that blog, I would be extremely turned off by waiting for 5 seconds just to have the page load start.

Hummingbird Cache - Baseline Response Time Distribution
Hummingbird Cache – Baseline Response Time Distribution

The response time distribution is pretty awful here. 50% of requests finished in under 5s, and 99% of requests finished in under 5.5s. In most load tests we like to see the P50 number be a lot lower than the P99 number. In a perfect world they’re both really low, but that doesn’t happen in most cases.

Cache Enabled Load Test

Our next test was the same as the baseline test, but with HummingBird cache enabled. We went with all the default options making no changes to the settings.

Hummingbird Cache – Cache Enabled Request Throughput
Hummingbird Cache – Cache Enabled Request Throughput

As expected of a caching plugin, throughput goes up a lot and settles in at around 175 requests/second with zero errors. This is a nearly 6x improvement in throughput. But what about the response times? How did this look to the end user?

Hummingbird Cache – Cache Enabled Response Times
Hummingbird Cache – Cache Enabled Response Times

The response time results are extremely promising. The average response time was around 95ms and the median was around 75ms. Most performance best-practices hope for your site to respond within 100ms, which this plugin easily accomplishes even under incredibly heavy load. Let’s break the response time numbers down further.

Hummingbird Cache – Cache Enabled Response Time Distribution
Hummingbird Cache – Cache Enabled Response Time Distribution

For 50% of our users, the response time was 75ms or less. For 99% of our users, response time was less than 160ms. These are great numbers and just what I would expect from a WordPress caching plugin.

Cache++ Load Test

Now that we’ve established that Hummingbird Cache does a great job under (somewhat) normal circumstances, lets see what happens if we double the traffic (400 concurrent users -vs- 200 concurrent users).

Hummingbird Cache++ – Cache Enabled Request Throughput
Hummingbird Cache++ – Cache Enabled Request Throughput

Event at 2X the number of users, we don’t see any errors and we see the throughput settling at about 325 requests per second. If you do the math, this is about 28 million requests a day. On a $5 box. Obviously this test is fairly naive, but it does show that the plugin can handle some serious traffic when needed.

Hummingbird Cache++ – Cache Enabled Response Times
Hummingbird Cache++ – Cache Enabled Response Times

The best part about this test is that even with incredible load the response time average and median are still below 180ms. Most users visiting a site would be extremely happy with response times in that range.

Hummingbird Cache++ – Cache Enabled Response Time Distribution
Hummingbird Cache++ – Cache Enabled Response Time Distribution

The response time distribution still tells a reasonable story. 50% of users see responses in 150ms or less and 99% see responses in 375ms or less. Solid performance from the Hummingbird Cache team.

Hummingbird Cache Conclusions

If you need a caching plugin for your site, Hummingbird Cache is a solid choice. It performs well, was easy to install, and was generally low friction. I found the user interface to be a little immature, but that doesn’t change the excellent performance we saw during our tests.

Want to run your own load tests? Sign up for Kernl!