I see it as unreasonable to expect all nodes to upgrade during a hardfork.
If you are intentionally waiting for that to happen, it's possible for an
extreme minority of nodes to hold the rest of the network hostage by simply
refusing to upgrade. However you want nodes to be able to protest until it
is clear that they have lost the battle without being at risk of getting
hardforked out of the network unexpectedly.

I think it makes sense to add a second fuse. After the 95% barrier has been
crossed, a 6 week timer starts that gives the remaining 5% time to upgrade.
If they still don't upgrade, they have intentionally forked themselves from
the network and it is not something that the remaining 95% need to be
concerned with.

On Sat, Jun 20, 2015 at 1:13 PM, Pieter Wuille <pieter.wui...@gmail.com>

> Hello all,
> I've seen ideas around hard fork proposals that involve a block version
> vote (a la BIP34, BIP66, or my more recent versionbits BIP draft). I
> believe this is a bad idea, independent of what the hard fork itself is.
> Ultimately, the purpose of a hard fork is asking the whole community to
> change their full nodes to new code. The purpose of the trigger mechanism
> is to establish when that has happened.
> Using a 95% threshold, implies the fork can happen when at least 5% of
> miners have not upgraded, which implies some full nodes have not (as miners
> are nodes), and in addition, means the old chain can keep growing too,
> confusing old non-miner nodes as well.
> Ideally, the fork should be scheduled when one is certain nodes will have
> upgraded, and the risk for a fork will be gone. If everyone has upgraded,
> no vote is necessary, and if nodes have not, it remains risky to fork them
> off.
> I understand that, in order to keep humans in the loop, you want an
> observable trigger mechanism, and a hashrate vote is an easy way to do
> this. But at least, use a minimum timestamp you believe to be reasonable
> for upgrade, and a 100% threshold afterwards. Anything else guarantees that
> your forking change happens *knowingly* before the risk is gone.
> You may argue that miners would be asked to - and have it in their best
> interest - to not actually make blocks that violate the changed rule before
> they are reasonably sure that everyone has upgraded. That is possible, but
> it does not gain you anything over just using a 100% threshold, as how
> would they be reasonably sure everyone has upgraded, while blocks creater
> by non-upgraded miners are still being created?
> TL;DR: use a timestamp switchover for a hard fork, or add a block voting
> threshold as a means to keep humans in the loop, but if you do, use 100% as
> threshold.
> --
> Pieter
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