What's happening in our world

Facebook is arguably one of the most well-known websites in the world. With over a billion active user accounts (despite some disagreements over how many of those are fake accounts), Facebook is also one of the largest PHP deployments in the world - if not the absolute largest. A custom written virtual machine dubbed the 'Hip Hop Virtual Machine' translates Facebook's PHP code into 64-bit x86 instructions for various kinds of heavy-duty server-side computation.



While Facebook is remaining relatively quiet about the entire process, you can look at a far more technical explanation of their plans at their Hip Hop Virtual Machine blog here. If you're a highly-skilled PHP developer who is also very familiar with the ARM server architecture, you might even consider applying for the job!

One of the holy grails of complex PHP application development is maximizing performance. Not only does better performance mean more manageable server loads, if you're scaling large enough, there can be a number of other dramatic gains in terms of power consumption and energy costs. Few companies are more familiar with this than the social networking giant Facebook, which is coded entirely in PHP and also just happens to be the largest social networking site on the planet. With over a billion active accounts, that's nearly 20% of the entire world's population - almost nobody else is as familiar with complex and robust PHP deployments as they are.

 

When it comes to web deployments of PHP applications, most developers initially choose to write the complicated code in PHP, but as the application scales and the usage levels increase, the more complex calculations are often re-coded using a faster server-based language such as C or C++. Facebook itself did this in the past, using a custom compiler named HipHop that translated the site's PHP code into C++ for faster execution. As in many large development environments, however, this eventually grew to create separate problems, which meant a new solution was called for.

 

Thus began the development of the HipHop Virtual Machine, or HHVM as it's more commonly known. Without getting too deep into the technical specifics, the HHVM translates PHP code into a custom bytecode known as HHBC (you guessed it, Hip Hop Byte Code) which is then processed by an x64 just-in-time compiler, along with a companion bytecode interpreter when absolutely necessary. This allows Facebook's entire staff of PHP developers to work on the entire codebase together, instead of dividing up the development process into PHP and C++, which can often lead to major headaches when it comes time to reconcile.

 

Joel Pobar, a developer at Facebook, cautioned that many developers hoping to gain performance improvements from implementing HHVM may not get the results they want, saying, "Chances are [your code is] spending too much time talking to the database or spending too time talking to the memcache caching layer." In other words, your performance bottleneck isn't likely to be execution speed, as there are other more typical culprits that can be identified by using benchmarking applications. The HHVM is strongly optimized towards  very large PHP codebases with very heavy usage loads, but it may be worth investigating for your next project.