Comment by agonz253

It's not purely a matter of cost, right? Say you want or need a highly available, high performance distributed database with externally consistent semantics. Are you going to handle the sharding of your Postgres data yourself? What replication system will you use for each shard? How will you ensure strong consistency? Will you be able to do transactions across shards? These are problems that systems like Spanner, CockroachDB, etc solve for you.