Peercoin block time is not 10 minutes

antaresus · January 26, 2019, 3:35pm

Everywhere in the Peercoin docs is written that Peercoin generates a block every 10 minutes, but it is a mistake, because considering PoS and PoW blocks Peercoin must generate a block every 8.57 minutes on average. In fact, last month, the Peercoin network generated a block every 7.78 minutes on average, and last year, every 8.23 minutes on average.

So, why does this mistake exist so long in the Peercoin docs?

Nagalim · January 26, 2019, 4:35pm

With difficulty changes and stochastic probability, it should be expected that average block time does not equal target block time. That said, I agree that block time in docs should be more explicitly spelled out.

I made a pull request for you:

If you see it pop up elsewhere, maybe we can try to use this thread to coordinate a campaign to disseminate this knowledge.

thehuntergames · January 26, 2019, 5:16pm

there are 2 loops at play. The blockspace(is this a word?) for POS is set to 10 minutes, while the space set for POW varies up to 2 hours(need verified). So yeah, the avg in total can be lower than 10 minutes, thats correct.

Buckkets · January 26, 2019, 5:16pm

It’s spelled out in the same way that Bitcoin’s is spelled out. Difficulty is based on a SMA that constantly adjusts over time which gives you a target time of 10 minutes.

Nagalim · January 26, 2019, 5:24pm

There are two difficulties. One is PoS, which adjusts to aim for a PoS block every 10 minutes. The other is a PoW difficulty, which adjusts to aim for a PoW block every 60 minutes. The result is a block, on average, every 8.57 minutes. This number is what we should use when calculating max txns/second, giving us 8 tps instead of bitcoin’s 7 tps.

thehuntergames · January 26, 2019, 5:34pm

I did a quick search and I encounted a list of POW block times: So it varies:

0 pos blocks in between: pow target = 20 min
1 pos blocks in between: pow target = 30 min
2 pos blocks in between: pow target = 40 min
3 pos blocks in between: pow target = 50 min
4 pos blocks in between: pow target = 60 min
5 pos blocks in between: pow target = 70 min
6 pos blocks in between: pow target = 80 min
7 pos blocks in between: pow target = 90 min
8 pos blocks in between: pow target = 100 min
9 pos blocks in between: pow target = 110 min
10+ pos blocks in between: pow target = 120 min

Nagalim · January 26, 2019, 5:45pm

We can all agree on PoS block spacing, for sure:

github.com

peercoin/peercoin/blob/master/src/main.h#L73


inline bool MoneyRange(int64 nValue) { return (nValue >= 0 && nValue <= MAX_MONEY); }
static const int64 MIN_TX_FEE_PREV7 = CENT;
static const int64 MIN_TX_FEE = CENT / 10;
static const int64 MIN_RELAY_TX_FEE = CENT / 10;
static const int64 PERKB_TX_FEE = CENT;
static const int64 MAX_MINT_PROOF_OF_WORK = 9999 * COIN;
static const int64 MIN_TXOUT_AMOUNT = CENT;
/** Coinbase transaction outputs can only be spent after this number of new blocks (network rule) */
static const int COINBASE_MATURITY_PPC = 500;
/** Threshold for nLockTime: below this value it is interpreted as block number, otherwise as UNIX timestamp. */
static const int STAKE_TARGET_SPACING = 10 * 60; // 10-minute block spacing 
static const int STAKE_MIN_AGE = 60 * 60 * 24 * 30; // minimum age for coin age
static const int STAKE_MAX_AGE = 60 * 60 * 24 * 90; // stake age of full weight
/** Maximum number of script-checking threads allowed */
static const int MAX_SCRIPTCHECK_THREADS = 16;
#ifdef USE_UPNP
static const int fHaveUPnP = true;
#else
static const int fHaveUPnP = false;
#endif

So the question is about PoW block spacing. I can’t find an equivalent declaration for PoW block spacing, so I’m open to the possibility that we adjust our PoW target based on number of PoS blocks. @thehuntergames can you link where you got this info?

Edit:

github.com

peercoin/peercoin/blob/master/src/main.cpp#L1237


const CBlockIndex* pindexPrevPrev = GetLastBlockIndex(pindexPrev->pprev, fProofOfStake);
if (pindexPrevPrev->pprev == NULL)
    return bnInitialHashTarget.GetCompact(); // second block


int64 nActualSpacing = pindexPrev->GetBlockTime() - pindexPrevPrev->GetBlockTime();


// ppcoin: target change every block
// ppcoin: retarget with exponential moving toward target spacing
CBigNum bnNew;
bnNew.SetCompact(pindexPrev->nBits);
int64 nTargetSpacing = fProofOfStake? STAKE_TARGET_SPACING : min(nTargetSpacingWorkMax, (int64) STAKE_TARGET_SPACING * (1 + pindexLast->nHeight - pindexPrev->nHeight));
int64 nInterval = nTargetTimespan / nTargetSpacing;
bnNew *= ((nInterval - 1) * nTargetSpacing + nActualSpacing + nActualSpacing);
bnNew /= ((nInterval + 1) * nTargetSpacing);


if (bnNew > bnProofOfWorkLimit)
    bnNew = bnProofOfWorkLimit;


return bnNew.GetCompact();
}

thehuntergames · January 26, 2019, 5:48pm

here the post I made back in 2014. Ratio of PoW blocks versus PoS blocks
code might have been changed since then( i doubed it tho)

Nagalim · January 26, 2019, 6:03pm

So all told, it is quite complicated and may even not be an equilibrium system. The ratio seems to be pretty close to the 1:6 PoW:PoS per hour that I used to make the 8 tps statement, so I still think we should aim to keep that in the table. However, how to explain this in a succinct way in the docs and abroad is quite a heafty task.

It is clear to me that the average block time will be less than 10 minutes, especially as PoW difficulty continues upward as we can expect it to. Thank you for your help elucidating this, we should add this information in as concise a form as possible to the website.

Nagalim · January 27, 2019, 2:46am

Please review before I PR this: