Today we've upgraded our PHP version from 7.3 to 8.1 for our v2 API. This is an upgrade we've wanted to do for quite a while, in-fact we've been running tests against 8.0.x versions of PHP for the past 12 months. It has taken some effort to upgrade our code due to the many changes between PHP versions and specifically the deprecating of old functions and changes to the behaviour of current functions

In addition to those required code updates we had to do a lot of performance testing due to the low latency nature of our API we're incredibly sensitive to code interpreter changes that could introduce performance regressions. And whilst PHP versions 8.0 and 8.1 introduce many great ways to improve performance including AVX instruction use, JIT compilation and improvements to OpCache there can be performance regressions dependant on the methods your code uses.

Often in coding there are a multitude of ways to complete the same goal, even a simple array iterating function can be implemented in many different ways with each having wildly different performance characteristics.

Thus we had to do a lot of performance testing. We've run billions of requests through PHP 8.x since it was released and through this testing we've identified and changed parts of our code where needed to get the best results. This work didn't just happen in the last month but has been an ongoing effort since November 2020 when PHP v8.0 was released.

And so today is the day that our v2 API is finally upgraded to a 8.x PHP branch and specifically v8.1.0 the latest and greatest version of PHP.

With this change we're seeing a steady 25% latency improvement over our previous code which directly translates into being able to handle more requests per second. But remember this isn't just down to us switching PHP versions this improvement also includes all the work we did to bring our code up to the PHP 8 implementation standard. Many of our code changes by themselves have improved performance simply by using newer or faster functions and methods.

One of the pitfalls when doing an upgrade like this is code debt. We now support four different versions of our v2 API and the oldest of these needed more work than our newest to even execute consistently under PHP v8.x. We also had to recompile some of our own libraries that we include within our PHP environment to bring them up to 8.x compatibility.

You may have read in a previous blog post how we had rewritten our caching library. The main reason for this was to bring support for builds of PHP 8.x although we were able to improve performance simultaneously just through the natural iterative design process.

At current only our v2 API is using the newest PHP 8.1 interpreter but we have done testing with the customer dashboard and other parts of our site including administrative backends and it looks promising for a full site rollout over the next few months.

So that's todays update, thank you for reading and we hope everyone is having a great weekend.