Take the 2-minute tour ×  I'm working with a site that was built
in Drupal and generally runs well. After some optimization it
takes 20-75MB of memory and 0.5-2s for most requests. But once
in a while it will take 15-20s and the process will run over
1GB+ memory usage.  I've tried tracing the time and memory usage
at the beginning and end of the PHP execution (putting the code
in Drupal's index.php) and it shows nothing unusual (it reports
a difference of 1 seecond between the start and end, and memory
usage goes up 72MB in one example). Somehow PHP is using a lot
of resources but not within the actual PHP code.  This was first
observed with apache. Moving to a new server (using standard
Ubuntu packages) made the site a bit more reliable, but it still
happens. Even after switching to nginx+php-fpm and turning off
apache entirely, the php-fpm processes show the same memory
usage pattern. Other than standard PHP modules the only extras
are memcache, stats, and xhprof.  What could reveal why PHP is
using so much