Meeting Jonny Harris: WordPress Performance with Blackfire

By Thomas di Luccio, on Feb 15, 2023

Jonny Harris is a WordPress core contributor and committer based in the UK, and a member of the WordPress Performance Initiative. This group teams up with Google and Blackfire to optimize the performance of the PHP Framework that powers an estimated 43% of the world’s applications.

Jonny has been coding with WordPress since 2006, when, at the age of 16, he wanted to start blogging. He gave WordPress a try as it was then, and still is today, the leading open-source blogging framework.

 A teenager with limited resources, the first motivation to pick open-source was the cost. It was the opportunity to start something new for free. Then, Jonny figured out the power of open-source contribution. He realized that the problems impacting many users could be fixed all at once. 

As a coder and a maker, Jonny installed a local version of WordPress 1.5 and started playing around with it. He explored WordPress’s codebase and its documentation, teaching himself how to code along the way. He wrote his first template, which was the beginning of a lasting relationship with WordPress.

Quite often, the journey ends up being more important than the destination reached. Beyond  simply blogging, Jonny built his own path toward web development and open-source contribution. He was looking for a hobby and found a career.

After graduating with a degree in Computer Network Management and Design, he joined Xanda, a small London-based web agency, still coding with and advocating for WordPress. The company grew steadily until there were over 12 WordPress developers.

It was then time for a new chapter in his professional journey. He joined The Times, then the UK’s largest magazine publisher with over 80 titles. There, Jonny took on the challenge of WordPress Multisite and fleets of WordPress applications self-hosted on AWS.

The performance issues faced by Jonny and his team were as important as the stakes for this publisher were high—those fleets of WordPress websites were the cornerstone of their online editorial strategy. They were quite unhappy with the results and the process of New Relic, which they were using at the time. And too many of the performance issues originated in WordPress Multisite core code.

Jonny then started opening Trac issues and writing patches. He contributed to the code base and helped improve its performance. About a year later, he was promoted to maintainer of WordPress Multisite. Over the years, he oversaw the users, site health, and the REST API.

In 2021, the WordPress Performance Initiative was created and driven by Google and Yoast.  XWP, the agency he then worked for, specialized in performant WordPress applications. There was a global effort to optimize and speed up WordPress, and Jonny was given a new way to contribute to the open-source framework.

As of now, Jonny Harris has been working with and on WordPress for over nine years. And that relationship got even stronger when he was made Core Committer. A core committer is a maintainer of an open-source project with merge access. That means they actually have permission to update the code base, not only to suggest changes or make requests.

This is quite an honor and the recognition of a long and amazing track record of contributions. It’s not only great power, it’s also a great responsibility as each update made on the code base impacts so many people, developers, and web users around the world.

WordPress takes pride in guaranteeing long-lasting backward compatibility. This not only means that all changes being made and new features added have to be compatible with older versions of PHP, but they also need to work with already existing plugins and themes that rely on older functions and hooks.

This makes the work of the Performance Initiative even more challenging and exciting. It’s about laying new grounds for WordPress without forgetting its past or leaving people behind. 

Now Jonny, as part of the Performance Initiative, finally has the opportunity to work on issues he encountered up to seven years ago. Those issues act sort of like time capsules notes left by a past self for when the time comes and the proper tool is finally made. 

That tool is Blackfire.

Jonny Harris used Blackfire extensively when working on the WordPress 6.1 Misha release. There were quite a few performance issues to figure out, including new regressions that had also been identified in the translations management as well as a nasty recursive loop while parsing the theme.json file.

Blackfire Profiler played a decisive role in the identification of these issues. Jonny and his team were able to pinpoint them down to the precise function calls. They also identified which lines of which files to look for the origin of those performance problems. And they shared those findings with other WordPress developers.

Those issues were identified and fixed throughout WordPress 6.1’s betas and release candidates. In fact, the 6.1 release note states over 25 performance-related tickets closed. A comprehensive breakdown also reveals breakthroughs in WP_QUERY, the REST, and CACHE APIs, among others.

The work of Jonny Harris and the Performance Initiative continues—these amazing improvements are just the beginning. If many tools on the WordPress market aim at speeding up applications, WordPress should be among the most efficient PHP frameworks. 

And in this case, being the most efficient doesn’t just mean faster page load times or speedier infrastructures—although that’s certainly a major part of it. It also means reducing our energy consumption to better protect the health of our world. 

Blackfire and believe in performance optimization and the significant reduction of resources needed to power applications. We believe you don’t need to fix problems with another server. WordPress powers up to 43% of the world’s applications, meaning each performance improvement, no matter how small, could have a massive impact on the web’s global carbon footprint.

We are grateful to have crossed paths with Jonny Harris and to be part of the Performance Initiative journey. We commit to taking sides with all open-source contributors who aim at making the world a better and more efficient place—one commit at a time.

Thomas di Luccio

Thomas is a Developer Relations Engineer at for He likes nothing more than understanding the users' needs and helping them find practical and empowering solutions. He’ll support you as a day-to-day user.