title: What means (timeout) in "strace" -output? (mysql / php analyse)
body: <p>I have a problem with a SQL query, which for reasons (which I do not understand), according to "strace" a (timeout) and will get up to run X-times?</p>
  
  <blockquote>
    <p>poll([{fd=6, events=POLLIN|POLLPRI}], 1, 0) = 0 (Timeout)</p>
  </blockquote>
  
  <p>The PHP script which executes the query first looks in the database if the appropriate e-mail address is already in the database, if not it will be added it and if no error has occurred, an email is sent. </p>
  
  <p><strong>Server:</strong> Ubuntu 14.04.3 LTS</p>
  
  <p><strong>DB:</strong> mysql Ver 14.14 Distrib 5.5.44, for debian-linux-gnu (x86_64) using readline 6.3</p>
  
  <p><strong>Table:</strong> InnoDB</p>
  
  <p><strong>SQL:</strong> (Example | Duration of 1 query: 0,031 sec.)</p>
  
  <pre><code>SELECT SQL_NO_CACHE user_email FROM mail_logging
  WHERE mail_id_fk IN (142)
  AND user_email = 'tester@foo.bar'
  </code></pre>
  
  <p><strong>SQL:</strong> (EXPLAIN)</p>
  
  <pre>
  id  select_type table   type    possible_keys   key key_len ref rows    Extra
  </pre>
  
  <pre>
  1   SIMPLE  mail_logging    ref id_mail,mail_id_fk,user_email   id_mail 775 const,const 1   Using where; Using index
  </pre>
  
  <p><strong>strace:</strong> <a href="http://pastebin.com/FbYUZ1a3" rel="nofollow">http://pastebin.com/FbYUZ1a3</a></p>
  
  <p><strong>lsof:</strong> <a href="http://pastebin.com/RyQcbWmj" rel="nofollow">http://pastebin.com/RyQcbWmj</a></p>
  
  <p>edit: Thanks @VolkerK, now I see the problem :P</p>