I'm using PHP + Zend Framework for several CLI daemons. They take up quite a bit of memory. I'm assuming the Zend Framework part might be causing this, but I want to have facts showing me where the memory is wasted.
How can I determine where memory is wasted? Is this just a trial + error process? Also how can I improve garbage collection (I read some articles that this might also be an issue causing big memory usage).
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IME, PHP uses a huge amount of memory for parsing code - try building a simple script which does nothing other than explicitly including all the libs you're using and track the memory usage at start/finish. Compare this with what you see in your actual script.
Htbaa is partially correct - more recent versions of PHP have a much smarter garbage collector however the earlier versions still do garbage collection - they just don't find all the cases that the newer gc does. But because its garbage collection, you'll typically see something of a sawtooth in memory usage given a steady input load.
But good garbage collection won't fix bad code - if you've stored something in a variable which is not on the stack, then you need to unset it when you're done with it.
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I'd recommend using XDebug's profiler, which should give you the answers you need.
The profiler will generate a cachegrind file, which you can view in a tool such as KCacheGrind to see where your program's bottlenecks and memory usages are.
Find out more on XDebug's profiler page: http://www.xdebug.org/docs/profiler
What version of PHP are you running? Only PHP >=5.3 has a decent garbage collector. PHP <=5.2 can eat all your memory when used to run daemon scripts.