Firestore can run in one of two modes, Datastore mode or Native mode, and the Professional Cloud Database Engineer exam expects you to know which one fits a given scenario. Firestore in Datastore mode acts as a bridge between the older Google Cloud Datastore and the newer Firestore. It exists mainly for backward compatibility, so that teams with an existing Datastore application can move onto Firestore's managed infrastructure without rewriting everything. Native mode is the option for new projects, because it exposes the full feature set, including the real-time capabilities that Datastore mode does not provide.
Datastore mode keeps the entity-based data model that Datastore users already work with. Data is organized as entities rather than as the documents and collections used in Native mode, and existing application code that was written against Datastore continues to work. This is the point of the mode. It gives full backward compatibility so an existing Datastore workload can migrate to Firestore without an application rewrite.
In this mode you still get the strong consistency and high availability guarantees that Datastore provides. What you give up is the set of features that are specific to Native mode. There are no real-time features in Datastore mode, which means no live listeners that push changes to clients as the data updates. If an application depends on real-time updates, Datastore mode is not the right fit.
Native mode is the newer experience and the one to reach for on a brand new project, since it lets you take full advantage of Firestore's features. The clearest difference for the exam is real-time. Native mode supports real-time listeners and the document-and-collection model, while Datastore mode keeps the entity model and leaves out the real-time features. Both modes run on the same managed Firestore infrastructure, so the choice is about the data model and the feature set rather than about scalability or availability.
One practical constraint worth remembering is that a mode is chosen per database and is not something you switch back and forth on casually. That makes the decision at creation time the one that matters, which is why the exam frames it as a choice between starting fresh and carrying an existing application forward.
The guidance is straightforward. For a new project, use Native mode, because it gives you the complete feature set, including real-time updates. Datastore mode is the right choice when you have an existing Datastore application and want a smooth transition onto Firestore. In that case Datastore mode functions as a stepping stone. It lets the team adopt Firestore's managed infrastructure and scalability now, with backward compatibility preserved, and modernize the application toward Native mode features later when there is time to do the work.
So when a question describes an existing Datastore application that needs to migrate without a rewrite, Datastore mode is the answer. When it describes a new build, especially one that needs live updates pushed to clients, Native mode is the answer. Keeping those two cues separate covers most of what the Professional Cloud Database Engineer exam asks about Firestore modes.
Our Professional Cloud Database Engineer course covers Firestore in Datastore mode alongside Native mode and Firestore's consistency model, with practice questions that drill these distinctions.
