The last two days I’ve been writing an Object cache in PHP as part of a larger project. I released it today as open source so it will help those doing something similar and get some that helpful feedback open source offers.

PHP Object Cache is a Memory Object cache, implemented with PHP Sockets. It runs on PHP4 or PHP5+ and requires your PHP build to have sockets enabled.

The project is a web (browser) based chat system called Joomla Ajax Chat. The initial development of the chat was 3 and a half years ago, so many of what worked then (HTTP Polling and AJAX) is becoming old school now and not as efficient as what is possible with browsers today.

One of the new features is implementing comet like HTTP, which essentially means keeping the HTTP connection open for as long as you can. XMPP defined a specification for this called BOSH for their Instant Messaging Protocol to work over HTTP. With a good implementation, Comet can be very efficient.

Our problem is that we have to implement Comet on regular ol’ Apache, Lighty, Nginx, IIS servers running different versions and builds of PHP. The code will have to run on the average shared hosting, dedicated servers to cloud based solutions. The other problem is it has to run on top of Joomla, and other CMSs. A call to a minimal Joomla page alone, is around 5-6 database reads and one or two writes and about 5-6Mb of ram. It wouldn’t take much to crash a shared hosting account trying to implement comet on top of that.

So the solution would have to be an object cache of some sort, even if it means a file based cache (last resort). Thus, PHP Object Cache, which hopefully will work for the percentage of shared server that allow sockets. The idea it to take the most intensive IO processes, such as session management, chat events and put them into the Object cache. When everyone online has viewed what they need from the cache, flush that bit to the database or some other persistent storage if needed.

Since the browser is able to do more as time goes on, hopefully php on old shared servers can keep up.

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