App Engine provides a clear approach to running fully managed services in the cloud. Google created Cloud Datastore as a persistence solution with many of the same qualities – flexibility, scalability, and ease of use. While Datastore has proven to be a great product for many applications, it suffers from limited query support and an inability to model highly relational data. In October of 2011, Google released the developer preview of a fully managed MySQL database as a response to popular demand from App Engine developers.
"You can now choose to power your App Engine applications with a familiar relational database in a fully-managed cloud environment. This allows you to focus on developing your applications and services, free from the chores of managing, maintaining and administering relational databases."