PathFinder status

[Jammet]

How does the java based vanilla server handle it when there are so many many more mobs to keep in check, when someone has, say, 1000 or so amassed in a tiny space, for farming eggs, or something like that?

Does it maybe just take a certain number of these animals and move them around, while the others are set to stay put and idle until it's their "turn"?
(Hope it's okay if I participate, I find the whole thing very interesting).