I'm glad now, instead of PPLNS, we're considering the double geometric method, which I assume is similar to the current method. Is there a post explaining it?
Sure, but get ready for disappointment. It is a hybrid between PPLNS and the geometric method, and I recommended to Inaba to set it to be close to PPLNS, to reduce the variance. I still don't get the problem with PPLNS. But this is exponential PPLNS rather than 0-1 PPLNS, so your objections may not apply.
Especially in the long blocks, people hop-off to leave and mine on other pools.
They don't gain anything from doing that. The fact that the round was long does not affect the payouts of futures shares they submit.
I agree with you. I didn't claim they have a gain from hopping off the pool. All I said is that people get tired when the block gets long and decide to mine on other pools. Maybe it's not the only reason, but I often see the total hash rate fall from 80 to 60GH/s over the course of a long block. In the last monster block, I remember we fell to about 50 GH/s. Then it becomes important that the scoring method makes people stay in the pool. If you didn't have that I assume more people would be leaving. I don't have a way of proving this, though.
Well. If there's a need, I can design a method that really does encourage people to stay. But, not being a magician, I cannot design a method that encourages people to stay
and gives people a reason to start mining in the first place. And, I think any method which is not 100% hopping-proof (expected payout etc. per share always the same) is ignoble, and that the problem you describe is negligible.
1) In the first N shares of a block, PPLNS is equivalent to PPS.
In the mineco.in example, N was 750k shares, and with Eclipse's hash rate, it would be reached in about 17 hours. So if a block is shorter than that, it would practically be found using PPS method.
I don't follow this logic at all. You are paid once per share in PPS. In PPLNS, you can be paid for every share 0,1,2 or any number of times.
2) After the pool has mined N shares for a block, during the time it takes to mine N shares by the pool, one can hop in for n << N hours and would have (N-n) hours without any decay in reward.
They do not gain anything from doing this, but the pool's hash rate is reduced. If they switch to a giant pool, they get steady payout.
They could have started mining in the giant, low-variance pool in the first place. If they started mining for you and then leave, you can't force them to stay.
You may be interested to know that unlike PPLNS but like the geometric method, double geometric can reduce pool-based variance (the variance caused by the pool being too small). This is at the cost of increased operator risk, though, and I don't know how risk-loving Inaba is.
3) In a long block, if many people follow the idea in (2), the pool's hash rate can drop to zero, stopping the rewards from decaying and the pool never succeeding in finding the block.
Obviously this is an extreme case, but if the hash rate drops significantly it will create a similar scenario where the pool becomes "cursed".
I don't see that realistically happening.