title: Zend_Session::Start intolerably slow (but only sometimes)
body: <p>Yes, I've read <a href="https://stackoverflow.com/questions/10385582/session-start-seems-to-be-very-slow-but-only-sometimes">session_start seems to be very slow (but only sometimes)</a>, but my problem is slightly different.</p>
  
  <p>We have a PHP application that stores very simple sessions in memcached (elasticache to be specific), and have been monitoring our slowest-performing pageloads. Almost all of the slow ones spend a majority of their time in <code>Zend_Session::Start</code>, and we can't figure out why. It's a very <code>AJAX-y</code> front end, moving more and more toward a single-page app, making a number of simultaneous requests to the backend per pageload, and some of the requests take up to three to four times as long as they should based solely on this.</p>
  
  <p>It's not <em>every</em> request, obviously, but enough of them that we're concerned. Has anyone else seen this behavior? We were under the impression that memcache is not blocking (how could it be?), so the very worst would be a user has a bum session, but <code>multiple-second</code> wait times in <code>session_start</code> seems inexplicable.</p>