Presence probably takes more juice than the billion messages, and a good chunk of these servers can probably be there as fallbacks in case of failures. Just a supposition.
They do use C++ for the chat system, it's mainly the channels/presence (If memory serves me right) that are implemented in Erlang.
They do use C++ for the chat system, it's mainly the channels/presence (If memory serves me right) that are implemented in Erlang.