For Viaweb, users (ie, e-commerce sellers) paid $100+ per month. So a process per user isn't expensive. Shoppers didn't require so much state (just a shopping c

For Viaweb, users (ie, e-commerce sellers) paid $100+ per month. So a process per user isn't expensive. Shoppers didn't require so much state (just a shopping cart) so that part of the system kept all the state in a sharded database. There is some routing infrastructure required by the front end to route requests, time out after inactivity, and reload the process if they come back. But it can give very snappy response to have all the data needed to serve a request all loaded in memory.