This all applies to Ruby 2.1. In some cases a setting is not available in 2.0, this is noted. There is also a different with 1.9, 1.8, and REE --- these are not noted.
The number of heap slots to start out with. This should be set high enough so that your app has enough or almost enough memory after loading so that it doesn't have to allocate more memory on the first request (althogh this probably isn't such a big deal for most apps).
(todo: figure out how big a slot is. i think the answer can be infered from this code.)
So you're curious in learning this new thing called Reactive Programming, particularly its variant comprising of Rx, Bacon.js, RAC, and others.
Learning it is hard, even harder by the lack of good material. When I started, I tried looking for tutorials. I found only a handful of practical guides, but they just scratched the surface and never tackled the challenge of building the whole architecture around it. Library documentations often don't help when you're trying to understand some function. I mean, honestly, look at this:
Projects each element of an observable sequence into a new sequence of observable sequences by incorporating the element's index and then transforms an observable sequence of observable sequences into an observable sequence producing values only from the most recent observable sequence.