title: Does session_start in PHP prevent session expiration?
body: <p>I'm somewhat bewildered about using <code>session_start</code> in <code>PHP</code>. Should I use it in my scripts both when user initially creates session and when resumes it on consequent queries - or only when creating?</p>
  
  <p>Currently I do not call it when session already exists but I have found that session sometimes expires unexpectedly fast:</p>
  
  <p>For example, from public log of my site I see:</p>
  
  <pre><code>srinivasvarma678 09:14:34 27-Jun-14
      I've just logged in...
  
  ...
  
  srinivasvarma678 08:59:38 27-Jun-14
      I'm proud to tell I've just solved Vowel Count!
  </code></pre>
  
  <p>I.e. user's last interaction with site was at 8:59 and then in 15 minutes he needs to log in again (though <code>session.gc_maxlifetime=1440</code>)</p>
  
  <p>Could this behavior be explained by the fact I am not calling <code>session_start</code> every time?</p>