Functions that cause caching
There are some functions like file_exists(), stat and lstat and others that access files that are cached by php. You could run file_exists() and it may return TRUE if a file exists. If you delete that file and then run file_exists() again within the same script - I believe in the same execution, it would still return TRUE. So, if you'll be running these functions in the same execution time, you may want to run clearstatcache() after you run any of these functions.
http://us.php.net/manual/en/function.clearstatcache.php »
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