i don't know what you mean by "load balanced" to be honest

nostr relays are really just a database server in themselves

do you want to replicate the database, do you want to demand cache it, do you want to shard it? it's quite important what strategy you have in mind and whether that actually fits the use case

sharding is probably gonna need to use social graph and maybe combine that with geofencing

caching is the simplest, dumbest idea, where the relays that people use don't actually store much data but they proactively fetch new data and expire old data quickly to keep the space available

caching was the way i envisioned working it... you could extend it with broadcast so that new data is shared around immediately and then with the garbage collection, rapidly purged from the store when it gets no traffic

how you design that optimization depends entirely on how the data is going to be used, and propagated

inherently, replicated, RAFT/Paxos/pBFT databases ARE exactly replicas, you even used the word replica, you didn't mean replica because you just clearly said you didn't mean replica

replica is like a bitcoin node with the same blockchain, that's a replica, all replicated database protocols make replicas, and individual replicas don't have the option to decide not to store data arbitrarily

what you are talking about is a caching strategy, which means you want to do garbage collection and broadcast