[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.

[YetAnotherNick]

Just curious, why would distributed be design requirement? Is individual machine failure likely in AWS/GCP? The only failure I have seen in region level issues which spanner or dynamo don't help with AFAIK.

[agonz253]

Individual machine failure is not likely, but we're hypothesizing the need for multiple shards for high performance. So now we have more machines and so the probability of failure increases. So we need to add replication, but then we need to deal with data getting out of sync, etc.... As others have mentioned though, these issues only really become important at a certain scale.