After reading several books and web pages related to App Engine Datastore, I have decided to write this brief post explaining the basic ideas behind this Datastore, leaning mainly on the book Google App Engine Java and GWT Application Development and information that you can read at https://cloud.google.com/appengine/docs/java/storage.
App Engine Datastore is a schemaless NoSQL datastore with automatic caching, a sophisticated query engine, and atomic transactions. It is based on Google’s Big Table design.
The Datastore’s design has a focus on scalability and it is not a relational database. This design allows its data to be partitioned, or sharded, and it is distributed in a way that makes partitioning data and performing queries extremely efficient.