[stonemetal12]

>my understanding is that until recently you had to vacuum it every once in a while.

You still do. The auto Vacuum daemon was added in 2008ish, so it isn't too bad. Just more complexity to manage.

> it's also using some kind of threading model

It does a process per connection just like web servers did back in the day when C10k was a thing. A lot of the buffers are configured per connection so you can get bigger buffers if you keep the number of connections small.