I'll bet it's async replication with streaming. Anything else costs too much in complexity and performance. Of course the cost of such a setup is a small window

I'll bet it's async replication with streaming. Anything else costs too much in complexity and performance. Of course the cost of such a setup is a small window where data loss is possible -- but if you're ok with this service you're already ok with data loss because the daily backups lose any add+delete operations you do in a day (unless you have triggers that copy the deleted data in a shadow table)