There's a whole database, Datomic, that works roughly this way -- not the UDP multicast but the idea of having a slightly more nuanced consistency/availability/partition tolerance tradeoff by having a thin transaction organizer which is not partition tolerant and officially states which one came first and second, upstream of the replicas that grant normal availability. I would have liked the discussion about Raft/Pax…
What's the state of Datomic these days? I stopped keeping up with it a while back when I stopped really paying attention to the Clojure space in general. Last I remember hearing it was still a purely pay to use their instances sort of deal.
There's on-prem which is the original model, and then the newer Datomic Cloud (came about in ~2018) which is installed from AWS Marketplace and billed through AWS. There are some feature differences between them. With on-prem there are free and $$ licensing options. Might be that the on-prem gratis licensing options were more limited before.
Some of the cool kids in Clojure world seem to have moved over to XTDB these days.