[Bitcoin-development] Mechanics of a hard fork

Roy Badami roy at gnomon.org.uk
Thu May 7 22:08:48 UTC 2015

On Thu, May 07, 2015 at 11:49:28PM +0200, Pieter Wuille wrote:
> I would not modify my node if the change introduced a perpetual 100 BTC
> subsidy per block, even if 99% of miners went along with it.

Surely, in that scenario Bitcoin is dead.  If the fork you prefer has
only 1% of the hash power it is trivially vulnerably not just to a 51%
attack but to a 501% attack, not to mention the fact that you'd only
be getting one block every 16 hours.

> A hardfork is safe when 100% of (economically relevant) users upgrade. If
> miners don't upgrade at that point, they just lose money.
> This is why a hashrate-triggered hardfork does not make sense. Either you
> believe everyone will upgrade anyway, and the hashrate doesn't matter. Or
> you are not certain, and the fork is risky, independent of what hashrate
> upgrades.

Beliefs are all very well, but they can be wrong.  Of course we should
not go ahead with a fork that we believe to be dangerous, but
requiring a supermajority of miners is surely a wise precaution.  I
fail to see any realistic scenario where 99% of miners vote for the
hard fork to go ahead, and the econonomic majority votes to stay on
the blockchain whose hashrate has just dropped two orders of magnitude
- so low that the mean time between blocks is now over 16 hours.

> And the march 2013 fork showed that miners upgrade at a different schedule
> than the rest of the network.
> On May 7, 2015 5:44 PM, "Roy Badami" <roy at gnomon.org.uk> wrote:
> >
> > > On the other hand, if 99.99% of the miners updated and only 75% of
> > > merchants and 75% of users updated, then that would be a serioud split of
> > > the network.
> >
> > But is that a plausible scenario?  Certainly *if* the concensus rules
> > required a 99% supermajority of miners for the hard fork to go ahead,
> > then there would be absoltely no rational reason for merchants and
> > users to refuse to upgrade, even if they don't support the changes
> > introduces by the hard fork.  Their only choice, if the fork succeeds,
> > is between the active chain and the one that is effectively stalled -
> > and, of course, they can make that choice ahead of time.
> >
> > roy
> >
> >
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