Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
I'm no BCH fan, but I agree with Scott that changes to the DAA may be of more than purely theoretical interest for BTC. Anyway just for those interested, below is an algo I've been playing with that adjusts difficulty every block, based only on the previous block's time and difficulty. I tested it a bit and it seems to adapt to hashrate swings pretty well. weight_n = 1 - e^-(blocktime_n / 1 hr)# 1 hr = exp moving avg window - too short? adj_n = (10 min / blocktime_n) - 1 difficulty_(n+1) = difficulty_n * (1 + weight_n * adj_n) It could also be tweaked to make the *historical* avg block time ~exactly 10 minutes, ie, to target > 10 min if past blocks were < 10 min. This would, eg, make mapping future block numbers to calendar times much more exact. On Nov 3, 2017 7:24 AM, "Scott Roberts via bitcoin-dev" < bitcoin-dev@lists.linuxfoundation.org> wrote: > The current DA is only sufficient if the coin has the highest > hashpower. It's also just really slow. If miners somehow stick with > SegWit2x despite the higher rewards in defecting back to bitcoin, then > bitcoin will have long block delays. High transaction fees will > probably help them defect back to us. But if SegWit2x manages to be > more comparable in price than BCH (despite the futures), hashpower > could very well oscillate back and forth between the two coins, > causing delays in both of them. The first one to hard fork to fix the > difficulty problem will have a large advantage, as evidenced by what > happens in alts. In any event someday BTC may not be the biggest kid > on the block and will need a difficulty algorithm that alts would find > acceptable. Few alts use anything like BTC's because they are not able > to survive the resulting long delays. I am recommending BTC > developers watch what happens as BCH goes live with a much better > algorithm, in case BTC needs to hard fork for the same reason and > needs a similar fix. Ignore the trolls. > > On Thu, Nov 2, 2017 at 7:39 PM, CryptAxewrote: > > Is there an issue with the current difficulty adjustment algorithm? It's > > worked very well as far as I can tell. Introducing a new one seems pretty > > risky, what would the benefit be? > > > > On Nov 2, 2017 4:34 PM, "Scott Roberts via bitcoin-dev" > > wrote: > >> > >> Bitcoin cash will hard fork on Nov 13 to implement a new difficulty > >> algorithm. Bitcoin itself might need to hard fork to employ a similar > >> algorithm. It's about as good as they come because it followed the > >> "simplest is best" route. Their averaging window is probably > >> significantly too long (N=144). It's: > >> > >> next_D = sum (past 144 D's) * T / sum(past 144 solvetimes) > >> > >> They correctly did not use max(timestamp) - min(timestamp) in the > >> denominator like others do. > >> > >> They've written the code and they're about to use it live, so Bitcoin > >> will have a clear, simple, and tested path if it suddenly needs to > >> hard fork due to having 20x delays for the next 2000 blocks (taking it > >> a year to get unstuck). > >> > >> Details on it and the decision process: > >> https://www.bitcoinabc.org/november > >> > >> It uses a nice median of 3 for the beginning and end of the window to > >> help alleviate bad timestamp problems. It's nice, helps a little, but > >> will also slow its response by 1 block. They also have 2x and 1/2 > >> limits on the adjustment per block, which is a lot more than they will > >> ever need. > >> > >> I recommend bitcoin consider using it and making it N=50 instead of 144. > >> > >> I have seen that any attempts to modify the above with things like a > >> low pass filter, starting the window at MTP, or preventing negative > >> timestamps will only reduce its effectiveness. Bitcoin's +12 and -6 > >> limits on the timestamps are sufficient and well chosen, although > >> something a bit smaller than the +12 might have been better. > >> > >> One of the contenders to the above is new and actually better, devised > >> by Degnr8 and they call it D622 or wt-144.It's a little better than > >> they realize. It's the only real improvement in difficulty algorithms > >> since the rolling average. It gives a linearly higher weight to the > >> more recent timestamps. Otherwise it is the same. Others have probably > >> come across it, but there is too much noise in difficulty algorithms > >> to find the good ones. > >> > >> # Degnr8's D622 difficulty algorithm > >> # T=TargetTime, S=Solvetime > >> # modified by zawy > >> for i = 1 to N (from oldest to most recent block) > >> t += T[i] / D[i] * i > >> j += i > >> next i > >> next_D = j / t * T > >> > >> I believe any modification to the above strict mathematical weighted > >> average will reduce it's effectiveness. It does not oscillate anymore > >> than regular algos and rises faster and drops faster, when needed. > >> ___ > >> bitcoin-dev mailing list > >>
Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
The current DA is only sufficient if the coin has the highest hashpower. It's also just really slow. If miners somehow stick with SegWit2x despite the higher rewards in defecting back to bitcoin, then bitcoin will have long block delays. High transaction fees will probably help them defect back to us. But if SegWit2x manages to be more comparable in price than BCH (despite the futures), hashpower could very well oscillate back and forth between the two coins, causing delays in both of them. The first one to hard fork to fix the difficulty problem will have a large advantage, as evidenced by what happens in alts. In any event someday BTC may not be the biggest kid on the block and will need a difficulty algorithm that alts would find acceptable. Few alts use anything like BTC's because they are not able to survive the resulting long delays. I am recommending BTC developers watch what happens as BCH goes live with a much better algorithm, in case BTC needs to hard fork for the same reason and needs a similar fix. Ignore the trolls. On Thu, Nov 2, 2017 at 7:39 PM, CryptAxewrote: > Is there an issue with the current difficulty adjustment algorithm? It's > worked very well as far as I can tell. Introducing a new one seems pretty > risky, what would the benefit be? > > On Nov 2, 2017 4:34 PM, "Scott Roberts via bitcoin-dev" > wrote: >> >> Bitcoin cash will hard fork on Nov 13 to implement a new difficulty >> algorithm. Bitcoin itself might need to hard fork to employ a similar >> algorithm. It's about as good as they come because it followed the >> "simplest is best" route. Their averaging window is probably >> significantly too long (N=144). It's: >> >> next_D = sum (past 144 D's) * T / sum(past 144 solvetimes) >> >> They correctly did not use max(timestamp) - min(timestamp) in the >> denominator like others do. >> >> They've written the code and they're about to use it live, so Bitcoin >> will have a clear, simple, and tested path if it suddenly needs to >> hard fork due to having 20x delays for the next 2000 blocks (taking it >> a year to get unstuck). >> >> Details on it and the decision process: >> https://www.bitcoinabc.org/november >> >> It uses a nice median of 3 for the beginning and end of the window to >> help alleviate bad timestamp problems. It's nice, helps a little, but >> will also slow its response by 1 block. They also have 2x and 1/2 >> limits on the adjustment per block, which is a lot more than they will >> ever need. >> >> I recommend bitcoin consider using it and making it N=50 instead of 144. >> >> I have seen that any attempts to modify the above with things like a >> low pass filter, starting the window at MTP, or preventing negative >> timestamps will only reduce its effectiveness. Bitcoin's +12 and -6 >> limits on the timestamps are sufficient and well chosen, although >> something a bit smaller than the +12 might have been better. >> >> One of the contenders to the above is new and actually better, devised >> by Degnr8 and they call it D622 or wt-144.It's a little better than >> they realize. It's the only real improvement in difficulty algorithms >> since the rolling average. It gives a linearly higher weight to the >> more recent timestamps. Otherwise it is the same. Others have probably >> come across it, but there is too much noise in difficulty algorithms >> to find the good ones. >> >> # Degnr8's D622 difficulty algorithm >> # T=TargetTime, S=Solvetime >> # modified by zawy >> for i = 1 to N (from oldest to most recent block) >> t += T[i] / D[i] * i >> j += i >> next i >> next_D = j / t * T >> >> I believe any modification to the above strict mathematical weighted >> average will reduce it's effectiveness. It does not oscillate anymore >> than regular algos and rises faster and drops faster, when needed. >> ___ >> bitcoin-dev mailing list >> bitcoin-dev@lists.linuxfoundation.org >> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
You launched the political football by coming here with a verbose 'recommendation'. Without a code submission in form of pull request to the core repo on github this was never a technical discussion. On Thu, 2017-11-02 at 19:53 -0400, Scott Roberts via bitcoin-dev wrote: > Whatever their failings from their previous code or their adversarial > nature, they got this code right and I'm only presenting it as a real > and excellent solution for the impending threat to bitcoin. As a big > core fan, I really wanted to delete the word Cash from my post because > I was afraid someone would turn this technical discussion into a > political football. > > On Nov 2, 2017 7:37 PM, "Gregory Maxwell"wrote: > On Thu, Nov 2, 2017 at 11:31 PM, Scott Roberts via bitcoin-dev > wrote: > > Bitcoin cash will hard fork on Nov 13 to implement a new > difficulty > > algorithm. Bitcoin itself might need to hard fork to employ > a similar > > algorithm. It's about as good as they come because it > followed the > > > This is the bitcoin development mailing list, not the "give > free > review to the obviously defective proposals of adversarial > competing > systems" mailing list. Your posting is off-topic. > > > > > ___ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
Whatever their failings from their previous code or their adversarial nature, they got this code right and I'm only presenting it as a real and excellent solution for the impending threat to bitcoin. As a big core fan, I really wanted to delete the word Cash from my post because I was afraid someone would turn this technical discussion into a political football. On Nov 2, 2017 7:37 PM, "Gregory Maxwell"wrote: On Thu, Nov 2, 2017 at 11:31 PM, Scott Roberts via bitcoin-dev wrote: > Bitcoin cash will hard fork on Nov 13 to implement a new difficulty > algorithm. Bitcoin itself might need to hard fork to employ a similar > algorithm. It's about as good as they come because it followed the This is the bitcoin development mailing list, not the "give free review to the obviously defective proposals of adversarial competing systems" mailing list. Your posting is off-topic. ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
On Thu, Nov 2, 2017 at 11:53 PM, Scott Robertswrote: > Whatever their failings from their previous code or their adversarial > nature, they got this code right and I'm only presenting it as a real and > excellent solution for the impending threat to bitcoin. As a big core fan, I > really wanted to delete the word Cash from my post because I was afraid > someone would turn this technical discussion into a political football. I urge my colleagues here to not fall for the obvious xkcd386 bait. The competitive advantage of prudence and competence is diminished if competitors are able to divert our efforts into reviewing their proposals. ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
Is there an issue with the current difficulty adjustment algorithm? It's worked very well as far as I can tell. Introducing a new one seems pretty risky, what would the benefit be? On Nov 2, 2017 4:34 PM, "Scott Roberts via bitcoin-dev" < bitcoin-dev@lists.linuxfoundation.org> wrote: > Bitcoin cash will hard fork on Nov 13 to implement a new difficulty > algorithm. Bitcoin itself might need to hard fork to employ a similar > algorithm. It's about as good as they come because it followed the > "simplest is best" route. Their averaging window is probably > significantly too long (N=144). It's: > > next_D = sum (past 144 D's) * T / sum(past 144 solvetimes) > > They correctly did not use max(timestamp) - min(timestamp) in the > denominator like others do. > > They've written the code and they're about to use it live, so Bitcoin > will have a clear, simple, and tested path if it suddenly needs to > hard fork due to having 20x delays for the next 2000 blocks (taking it > a year to get unstuck). > > Details on it and the decision process: > https://www.bitcoinabc.org/november > > It uses a nice median of 3 for the beginning and end of the window to > help alleviate bad timestamp problems. It's nice, helps a little, but > will also slow its response by 1 block. They also have 2x and 1/2 > limits on the adjustment per block, which is a lot more than they will > ever need. > > I recommend bitcoin consider using it and making it N=50 instead of 144. > > I have seen that any attempts to modify the above with things like a > low pass filter, starting the window at MTP, or preventing negative > timestamps will only reduce its effectiveness. Bitcoin's +12 and -6 > limits on the timestamps are sufficient and well chosen, although > something a bit smaller than the +12 might have been better. > > One of the contenders to the above is new and actually better, devised > by Degnr8 and they call it D622 or wt-144.It's a little better than > they realize. It's the only real improvement in difficulty algorithms > since the rolling average. It gives a linearly higher weight to the > more recent timestamps. Otherwise it is the same. Others have probably > come across it, but there is too much noise in difficulty algorithms > to find the good ones. > > # Degnr8's D622 difficulty algorithm > # T=TargetTime, S=Solvetime > # modified by zawy > for i = 1 to N (from oldest to most recent block) > t += T[i] / D[i] * i > j += i > next i > next_D = j / t * T > > I believe any modification to the above strict mathematical weighted > average will reduce it's effectiveness. It does not oscillate anymore > than regular algos and rises faster and drops faster, when needed. > ___ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Re: [bitcoin-dev] Bitcoin Cash's new difficulty algorithm
On Thu, Nov 2, 2017 at 11:31 PM, Scott Roberts via bitcoin-devwrote: > Bitcoin cash will hard fork on Nov 13 to implement a new difficulty > algorithm. Bitcoin itself might need to hard fork to employ a similar > algorithm. It's about as good as they come because it followed the This is the bitcoin development mailing list, not the "give free review to the obviously defective proposals of adversarial competing systems" mailing list. Your posting is off-topic. ___ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev