Just for one trillion (not "trillions"), that'd be 10 million function calls per server per day, ~7k per minute. Sounds about right to me. They'll surely want to leave some room for traffic spikes, server failures and unforeseen issues. Server uplink could also be a factor - at least that was the major bottleneck the last time I ran infrastructure serving lots of clients (about 100 million), but they are probably smarter about this than I was back then.