You are correct: a single server indeed has a high risk of losing data for the reasons you describe. I was talking about replication: by making sure all data is

You are correct: a single server indeed has a high risk of losing data for the reasons you describe. I was talking about replication: by making sure all data is replicated, for example, 4 times across 2 datacenters, you limit that risk a lot. There is a small timespan between writing data and all replicas picking it up, but if you make sure your servers aren't overloaded, this usually is very small. Having said that, I agree that there is room for improvement, for example using WAL and sync points like you describe.