So I haven't found this to be true. I'm always working with a single upstream server. I think the green pool management isn't straight forward, as it is event-driven. In other words, there aren't actually 100 simultaneous connections  going out to the upstream server, but 100 greenlets working on the downloads. The library's default is in the thousands (3000 iirc), but that was causing my router here at home to crash and I didn't actually get significantly better performance the more I increased this number after 100.