How does pool operator manage/distribute miners' mining power?

Hi,

I've been searching for that question in the forum but till now I haven't found any relevant thread. I bet that its been discussed somewhere, so please point me the thread and I will delete this one. If not, here my question in details.

The question is if there are N miners 1..N joining a pool with each having a hashrate h_i, so how does the pool operator distributes/manages the power properly? So as far as I understand how pooled mining works, the miner will get the block header via the get_work() request and mine on that to get valid shares/contributions. As my guess, the pool operator will distribute/manage the pool power though that get_work() request as well. However, there are several approaches for that.

1. The pool operator will specify some ranges of the nonce for miners to work on.
2. The pool operator will have some psudorandom function to generate the nonce and give miners different seeds.
3. The pool operator will let miners decide which nonce they should work.

My claim is that 3 won't work since if miner 1 submits a share S, other can submit S also without doing any work. And its not a good approach to optimize the pool power. Meanwhile 1 and 2 may work, but I'm not sure since miners join and leave the pool as they please. So I really want to know what is going on in real pools.

Thanks,