Firebase: a paas that google bought that included a real-time nosql db (also casually called firebase)

Datastore: googles OG serverless nosql db that was tightly baked into appengine as part of their own paas

After buying firebase google decided the db implementation was shit and set out to write their own. In typical google fashion they picked the most confusing name and called it firestore.

Rather than maintain 2 different nosql databases google quietly broke datastore free from appengine and migrated everyone’s data to firestore. But to maintain compatibility they kept both sets of APIs so now you have Firestore native (to get people to move off firebase) and firestore in datastore mode (for anyone who was using the og datastore). The 2 APIs still have specific features and access patterns hence the differences in billing.

You can access and manage firebase both from the GCP console and the Firebase console but it’s the same db, same as how firebase storeage is really just GCS. So that adds another layer of confusion.

Hope this helps.