For most of the last three months I have been keeping myself busy working on a project that's related to PHP and has involved looking at PHP performance.
It's been interesting and led me to try to understand a lot more about how the Zend engine works. I spent a lot of time reading some sections of the code, and using my favourite technique (yes, I'm sorry - it's printf()) to understand how things work.
After one particularly frustrating day I asked a colleague (Andy Wharmby) about the issue I was looking at. Then a miracle happened - he'd not only looked at it but had documented it (and many other things) in a set of charts.
When I read the charts a lot of things I didn't understand got clearer - so, with Andy's permission - I'm making his work available to the PHP world in case other people find them as useful as I did. You can download them in Open Office format here.
Andy asked me to make it clear that he wrote the charts almost two years ago, so there may be bits that are out of date, or even just plain wrong. If you see things that need to be fixed please send me a mail (email@example.com) and I'll be happy to update the slides. Andy made extensive use of Sara Golemon's blog posts and tools written by Sara and Derick Rethans. Apart from that, like me, he used printf() and a debugger to look at the source for the engine.
I know that Gwynne is working on internals documentation for PHP, I am really looking forward to that. These charts, although very useful, are no substitute for a well written manual section!