The POW Summit was an opportunity to put an end to the recurring excitement linked to sudden variations in the hashrate.
Bitcoin Hashrate
Jameson Lopp looked at the measurement of the global hashrate after a quote from Satoshi as an introduction to the POW summit:
“Proof of Work is the solution to the synchronization problem and allows you to know what the global consensus is without having to trust anyone. We don’t have to worry about who does the communications. No matter who tells you which chain is the longest, Proof of Work speaks for itself. »
Then getting to the heart of the matter, J. Lopp declared that trying to “Measuring hashrate is like trying to measure wind speed. Neither can be measured directly. They can only be measured indirectly and estimated after the fact. Knowing precisely the total hashrate of the network at a given time is meaningless.”
Presentation of Jameson LOpp from 1h02:
To explain the calculation of the hashrate, we must first define what mining difficulty is. This is a measure of the difficulty miners face in finding a block. That is to say the average number of hashes necessary to mine a block.
We “mine a block” when we find a hash lower than a certain value (target number). A hash is a number (expressed in hexadecimal) that is obtained by passing the header of a block through the SHA-256 algorithm. The smaller this number, the more the hash begins with zeros.
Mining difficulty is used to maintain the rate of one block of transactions approximately every ten minutes. Without this mechanism, blocks would be found faster and faster as the number of miners increases.
Why ten minutes? Turns out no one asked Satoshi Nakamoto. One explanation was that sufficient delay was required to allow blocks to propagate to all nodes.
The mining difficulty is therefore adjusted every 2,016 blocks. We’re talking about time (~ two weeks). If blocks are mined faster than 10 minutes on average, the difficulty increases (the target number decreases). If blocks are mined more slowly, the difficulty decreases (the target number increases).
Explanation :
The probability of a die roll being less than 2 is lower than the probability of being less than 5. The “2” corresponds to the target number. The lower the target number, the higher the difficulty. In the case of bitcoin miners, the smaller the hash to find, the lower the probability of finding such a hash (the difficulty increases).
The time elapsed to mine 2,016 blocks is determined based on timestamps. The formula for calculating the mining difficulty of a new era is:
Difficulty = (Previous epoch difficulty) x (Time elapsed in previous 2016 blocks / 20,160 minutes)
It is from this difficulty that we calculate the hashrate. The formula is:
Bitcoin Hashrate = [(Nombre de blocs trouvés en 24h / 144) x (difficulté de mining) x (232)] / 600
Knowing that :
-144 is the total number of blocks expected in a 24 hour period.
-(Difficulty) x (232) represents the average amount of hashes needed to find a block.
-600 is the number of seconds in 10 minutes.
All this to say that we encounter different hashrate values depending on the sites due to the period used in this formula.
In short, you should not get carried away when the bitcoin hashrate shows a sudden increase of 20% or 40%. Such variations are only linked to the fact that certain sites use a time step that is much too narrow (a handful of blocks).
Blocks are not found exactly every 10 minutes. Two blocks can be found a few tens of seconds apart, or on the contrary several tens of minutes apart.
Most websites publish an estimated hashrate over 24 hours. According to Jameson Loppthe ideal period is one week.
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