apache - What is the most efficient way to generate a UUID in PHP? -
    is there significant overhead (cpu, memory and/or io) in making repeat calls following function:   public function getuuid() {     return `uuidgen -r`; # -r = version 4 }   versus using all php implementation of generating uuid  (v4)?  if matters project using apache (prefork mpm) 2.2.22  , php 5.3.10  (with apc ).   my initial feeling benefit of doing generation of uuid in c library instead of in php more make system call overhead.  additionally uuidgen  being part of util-linux  package inherently trust more php library generate uuids correctly, i'm keen input.          i'd suggest profile problem. shell_exec()  php function spawns shell, might not come cheap think. php class mention seems call subprocesses. did tests (on os x) , generate 10.000 uuids php class in minute, opposed 40 seconds shell_exec('uuidgen') .   the php class seems call ifconfig  in addition shell_exec() , might reason bigger overhead.   also results vary hash algorithm choose.