Because the way that you will ultimately have to scale something like PostgreSQL for example is going to end up with eventual consistency which Firestore doesn’t have to deal with.
There's no reason for eventual consistency. Firestore is backed by BigTable and Spanner (both strongly consistent just like Postgresql). There's nothing magic about this - it just provide a pub/sub channel on the watched keys and automatically does a SELECT loop in the background once an INSERT triggers that key.
You can do the same thing on a simple by selecting by a `chatid` in a table that'll get the latest messages/inserts. Again, the only thing needed is the pub/sub layer, not an entirely different database.
You can do the same thing on a simple by selecting by a `chatid` in a table that'll get the latest messages/inserts. Again, the only thing needed is the pub/sub layer, not an entirely different database.