title: How to handle counter updates in the GAE datastore properly?
body: <p>Let's say I have page views counter in my datastore.
  In order to increase its value with each page display, I need to read the value, increment that and increase. How can I be sure that in case when 2 (or more) users view the page, both views are counted (i.e. there will not be a case that for user2 we read the counter value before we've updated that for user1)?</p>