title: Mysql: When exactly an event is logged in the binary log on the master
body: <p>When exactly an event on the master(update/insert/alter) is logged on the binary log ?</p>
  <ol>
  <li>When it started on the master server, it will be written to the bin log</li>
  <li>When it started and completed on the master, then will be logged</li>
  </ol>
  <p>In specific, I would like to know the behaviour in case of an ALTER
  If answer is 1, there won't be lag between master and slave in normal conditions only due to ALTERs started on the master.</p>