title: Pessimistic vs. optimistic concurrency control
body: <p>I have a question about pessimistic versus optimistic locking.
  Everybody says that "Optimistic locking is used when you don't expect many collisions.", for example:</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/6459433/which-concurrency-control-is-more-efficient-pessimistic-or-optimistic-concurrenc">which concurrency control is more efficient pessimistic or optimistic concurrency control</a></li>
  <li><a href="https://stackoverflow.com/questions/129329/optimistic-vs-pessimistic-locking">Optimistic vs. Pessimistic locking</a></li>
  </ul>
  
  <p>For a school project I need to find the 'break-even' point when pessimistic locking is more appropriate then optimistic locking.</p>
  
  <p>Now, I would like to know/understand why such a break-even point exists? How it is possible that pessimistic locking is more costly (in speed or memory usage?) then optimistic locking?</p>
  
  <p>I suspect it is because of the extra read-operation that pessimistic locking requires. But with optimistic locking this extra read-operation is also needed (only just before the save operation), right?</p>
  
  <p>Hopefully someone can explain this :)
  Thank you!</p>