In a new post to his blog Ilia Alshanetsky takes a look at PHP's output buffering feature and some interesting things he found when testing some recent code (hint: it has to do with PHP's "interesting" management of the buffer).
While profiling our application I came across a a rather strange memory usage by the ob_start() function. We do use ob_start() quite a bit to defer output of data, which is a common thing in many applications. What was unusual is that 16 calls to ob_start() up chewing through almost 700kb of memory, given that the data being buffered rarely exceeds 1-2kb, this was quite unusual.
Through a bit more testing he found that, if a buffer provided for content isn't enough, PHP automatically bumps it up by 10kb each time - a waste of resources if you only need a small subset of that. He includes a small patch he made to the PHP core API that allows for defining a custom buffer size and, if it's not enough, bumps up the buffer size by 1kb instead of 10kb.