I’m not sure why but it has been often requested over the years to have a command/data channel separation. This is especially true once you throw Mnesia into the mix and pass around large datasets.

Yes, according to some anecdotal evidence from the heavy users, it’s about 60-200 nodes for the default “distributed erlang” topology (mesh). To go beyond that, check out either partisan [1] [2] or scalable distributed erlang (don’t know if it’s usable yet).

[1] GitHub - lasp-lang/partisan: High-performance, high-scalability distributed computing for the BEAM.
[2] [1802.02652] Partisan: Enabling Cloud-Scale Erlang Applications

BEAM clusters are fully connected so when you connect a node into a cluster it connects to every other node and gossips with them. From the paper you linked to:

First, maintaining a fully connected mesh of Erlang nodes means that a system with n nodes must maintain O(n^2) active TCP/IP connections and this induces significant network traffic above 40 nodes

I am trying to find a reference for this but I don’t have one handy so this may be incorrect. I believe this is because everything goes over the same TCP connection. So every node, every 5 seconds, will send 2999 messages. That’s around 15M messages on the network and the TCP connections can’t do anything else while they’re waiting for a response.