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In August of this year we deployed a series of new server and storage devices which we expect will carry us through to 2011. One of the negative side effects of this deployment was that all of the sites and services we hosted on the new hardware performed significantly better than on the old configuration.

I hear you ask “how is that a negative side effect?” It meant that I put off the investigation into bench marking and tuning our server platforms simply because the move to newer hardware gave us significant gains. I had planned on doing some configuration tuning and system refinement, but the sheer increase in processing power meant that I didn’t bother with it back then.

Today, however, I decided to investigate what the addition of a PHP opcode cache would provide, and I was very happy with the results.

I came across an issue with running APC, the opcode cache developed by Rasmus and other core PHP developers, alongside the Zend Optimizer. The two are incompatible so you’ll have to play favourites and pick one or the other.

Installation of APC is easy on Ubuntu. There’s many guides online, but I found this one to be the most succinct. You end up installing the following packages (note: I didn’t have build-essential initially and PECL couldn’t build the package because I was missing make):

mlambie@prime:~$  sudo aptitude install php-pear php5-dev apache2-prefork-dev build-essential

The installation of APC is easy via PECL:

mlambie@prime:~$  sudo pecl install apc

Then enable the module by creating an apc.ini file:

mlambie@prime:~$ cat /etc/php5/apache2/conf.d/apc.ini
extension = apc.so
apc.enabled = 1
apc.shm_size = 48
apc.include_once_override = 1
apc.mmap_file_mask = /tmp/apc.XXXXXX

I ran some benchmarks using Apache Bench. The results were very encouraging. I saw a reduction in the time per request fall from 91ms to 37ms (250% improvement). The volume of requests per second increased from 11/sec to 27/sec (245% improvement). Lastly, 98% of all requests are served within 639ms instead of 1165ms (182% improvement).

Each actual apache process saw a significant memory reduction too, from 26MB down to 20MB (almost a 25% footprint saving). When you’ve got multiple processes running the reclaimed memory adds up quite quickly.

I found the figures staggering, and the improvements are actual, real things that are visible when interacting with the sites and applications hosted on prime.

It’s fair to say that we more then doubled our performance, from a single server, simply by adding PHP opcode cache. If you’re not running one on your server, you might want to consider why.