This architecture supported 1.5 million simultaneous users - with buddy lists and IMs, which means a full-mesh n^2 pub-sub system Novadays I can hold 1.5M open

This architecture supported 1.5 million simultaneous users - with buddy lists and IMs, which means a full-mesh n^2 pub-sub system Novadays I can hold 1.5M open sockets on single server ...