MongoDB was tested in a replicated setup, PG not, that's a pretty fundamental difference. Loosing acked writes in a master-slave replication with failover would

MongoDB was tested in a replicated setup, PG not, that's a pretty fundamental difference. Loosing acked writes in a master-slave replication with failover would be expected with a sufficiently large replication lag even for PG. MongoDB is about the last database I'd pick for any given scenario, but I acknowledge that there are people that have a usecase where it might be a good fit because the tradeoffs work out for them.