title: Google app engine transaction granularity
body: <p>I am writing a java application on Google App Engine(GAE) using objectify for datastore interface. I need to use transaction to make sure some of the operations in my app are atomic.  But I am confused about granularity of the database transaction i.e. if I am using a particular entity object in a transaction in a thread then which one of the following is true ? :-</p>
  
  <p>1) Can I use some other object of the same entity in a transaction in a different thread concurrently ?</p>
  
  <p>2) OR, Is it that at a time I can be making changes to only one object of a particular entity type</p>
  
  <p>If (2) is true, then what should I do if I expect to have multiple request to be coming for updating a particular entity type even though they will be for different objects under that entity type ?</p>
  
  <p>Thanks...</p>