title: What's the complexity of getting an instance by key on GAE?
body: <p>GAE has a built-in data type called <a href="https://developers.google.com/appengine/docs/python/datastore/typesandpropertyclasses#ReferenceProperty" rel="nofollow">ReferenceProperty</a>, which is actually a <code>db.Key</code> as it says. It can be used to get the corresponding instance and I wonder what the complexity is?</p>
  
  <p>The so called "Reference" is not like a reference in C++, which is the address, and the complexity of accessing it is O(1). And if it's just a key in the <code>key-value</code> system, I wonder it may take, like O(log) or what.</p>