Capped PPS with Recent Backpay
Whenever a block is found, the most recent 25 BTC (a CPPSRB round; one block reward/subsidy) worth of unpaid shares are paid.
Using the proportional concept of rounds, a long round results in the earlier shares being shoved into storage (shelved) rather than paid by the block, and a short round pays the entire round plus the most recent "storage" (shelved) shares found which were not already paid.
Compared to PPLNS, no share is ever paid twice, but old shares (that missed out on being rewarded due to poor luck in the past) have a chance to be paid when the pool is lucky.
When a block is found:
- Go back 25 BTC into the share log, and reward those at PPS price.
- Delete those shares from the log
- If the entire database was paid and there are still funds left, include it in the next block's reward
When a block is orphaned:
- Undelete the shares rewarded for it
In simple terms, what is a summary of CPPSRB?
CPPSRB is a Maximum Pay-Per-Share reward system variant (MPPS). The pool will pay miners as much as is possible using the income from finding blocks, but the pool can never go bankrupt because of high variance and miners have lower variance overall than other reward systems, such as proportional, PPLNS, DGM, etc.
What is this "Shelved Shares" business?
Shelved Shares are simply shares that you have somewhere in the full pool share log that are not yet close enough to the top of the share log to be paid when the next block is found.
How am I paid for my Shelved Shares?
CPPSRB shares are paid in a last-in-first-out order. When a block is found, the share log is processed from the top downward and shares are paid until one full block reward (25 BTC now) worth of shares are paid. If the current round is a "lucky" round (ie: it took less than 1*network_difficuly shares to find the block) then the top of the share log will contain shares from the current round AND some shelved shares from previous rounds, which will then be paid.
So the short answer is: Some amount of shelved shares are paid for every lucky block (on the stats page, a block with a luck > 100%). Depending on how far down in the share log your shelved shares are determines if they're paid by the current block or not. (See your userstats page and note the estimated change in shelved shares. Negative means that amount will be paid if a block is found now.) (In the works: Share log visualization)
Does the pool *owe* me payout of my Shelved Shares?
No. The shelved shares are shares that pool itself never received any funds to pay in the first place. The only way shelved shares can be paid is as described above. (If someone of course wanted to donate bitcoins to the pool buffer, then of course more would be paid.)
Do my shares retain their value from the time they were mined regardless of difficulty changes in the future?
Yes, shares are stored in the share log with their value as a portion of block subsidy at the time of mining and this does not change, ever.
Why the move to CPPSRB from SMPPS? (Eligius specific)
SMPPS was becoming a burden to the pool when new miners were basically mining just to pay the "extra credit" for miners who had stopped contributing to the pool entirely long ago. CPPSRB pays the *newest* shares first and no shares are ever underpaid. So, no one is ever "penalized" for past bad luck in the way SMPPS did this.
How does CPPSRB compare to straight PPS?
With "straight PPS" the pool takes the risk of paying miners during unlucky rounds and recovering the losses during lucky rounds. with CPPSRB, the pool only pays miners as much as is possible during unlucky rounds, and makes up the difference through "shelved shares", which are paid during lucky rounds.
Since Eligius has no mining fees, your shares are put in the share log at 100% PPS. Over time, payouts will average out to as if you had mined at 100% "straight PPS", or close to it, depending on luck.
It is useful to note that it is statistically impossible to offer and run a 100% (or higher) "straight PPS" pool indefinitely, where CPPSRB can run indefinitely with no risk to the pool or miners of not being paid their fair share for their work.
(More to come)