Update 2 (01/31/19)
As of today, Cloud Firestore is no longer in Beta and is Generally Available:
https://cloud.google.com/blog/products/databases/announcing-cloud-firestore-general-availability-and-updates
This means that Cloud Datastore is no longer an option for new projects (you can keep using it on existing projects). New projects that want to use the Datastore API can use Cloud Firestore in Datastore mode.
Update 1
As you we have noticed, we've expanded Cloud Firestore since this question was posted.
This means Cloud Firestore now has 2 modes:
- The original launch was 'Native mode'
- The new launch adds 'Datastore mode'
'Datastore mode' is the 3rd gen of Cloud Datastore. 1st was called Master/Slave Datastore, 2nd was High-Replication Datastore (HRD) that was rebranded as Cloud Datastore in 2013.
The below answer is still largely relevant since both modes are currently mutually exclusive, so you need to pick one or the other.
The main differences are the improves of Cloud Firestore in Datastore mode over Cloud Datastore. The biggest ones are:
- Write through-put per entity group now unbounded (was 1 write/second)
- Transactions no longer limited to 25 entity groups
- All queries now strongly consistent.
Also note Cloud Firestore regardless of mode is beta, so the new Service-Level Agreement (SLA) doesn't go into effect until the product reaches General Availability (GA).
Original Answer
Cloud Datastore (CD) and Cloud Firestore (CF) are similar, however different in significant ways.
CF is mobile-centric with direct from mobile client functionality with the Firebase SDKs and Rules functionality. CD is server-centric with a wider range of server client libraries, as well as some mature frameworks on App Engine Standard that bundle in memcache functionality.
CF has a newer storage layer that is strongly consistency in the same way as Cloud Spanner, however, it's still in beta without an SLA. CD's storage layer is only strongly consistent within entity-groups and eventually consistent across entity-groups, however, it is GA with a 99.95% SLA for the Multi-Region locations.
CF is only available in the US Multi-Region at this time. CD is available Cloud across a dozen locations including places in the Americas, Europe, Asia, and Australia.
CF during beta has a guideline limit of 2500 writes/second while we build experience monitoring and tuning the system prior to GA, whereas CD will happily handle >1M writes/second (please reach out to your account rep first though).
CF and CD's set of query capabilities are overlapping but not the same. Overall CD has a broader set of query capabilities we haven't built in CF yet, so you'd have more flexibility in CD.
Overall, I'd consider this list to see if any of the differences make or break what you're trying to build then pick the DB that fits closest to your needs.
