The problem with postgres scaling is that you have to have a single master which means horizontal scaling really only gives you more reads and a failover. Eventually you wont be able to find a server big enough to handle all the writes, and if you get enough reads with even a small number of writes single master setups fall over. Distributed computing gets complicated very quickly but the gist here is basically that you need to be able to have multiple instances that can accept writes. Lots of literature on this but good starting points imo would be the paxos paper https://lamport.azurewebsites.net/pubs/time-clocks.pdf and dynamo db paper https://www.allthingsdistributed.com/files/amazon-dynamo-sos...