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From: Jeff Garzik <jgarzik@bitpay.com>
Date: Fri, 3 Oct 2014 19:12:11 -0400
Message-ID: <CAJHLa0NRNEQLqA2E=ysXsKw6hWS-H9X_AFYK4ckC4-_Bk=qbSA@mail.gmail.com>
To: Mike Hearn <mike@plan99.net>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>,
	Flavien Charlon <flavien.charlon@coinprism.com>
Subject: Re: [Bitcoin-development] [BIP draft] CHECKLOCKTIMEVERIFY - Prevent
 a txout from being spent until an expiration time
Precedence: list

RE " It's not like other software where people can choose to skip an
upgrade and things still work just like before."

If you're a minority, sure you can.  Still a few nutters out there on
a 0.3.x codebase, including one or two inattentive,
now-inconsequential miners.

There is some headroom built in for just that... less disruptive
upgrades that don't require 100%.


On Fri, Oct 3, 2014 at 4:58 PM, Mike Hearn <mike@plan99.net> wrote:
> Alright. It seems there's no real disagreement about how the opcode behaves.
> Perhaps a time limit would be appropriate to stop people creating outputs
> locked for 100 years .... is bitcoin even likely to exist in 100 years? The
> entire history of computing is not even that old, seems hard to imagine that
> it'd be good for anything beyond wasting space in the database. But this is
> a minor point.
>
> So I guess it's time to start the deployment discussion.
>
> Bitcoin is a consensus system. It works best when everyone is following
> exactly the same rules at the same time. A soft fork works against this
> principle by allowing nodes to think they're following the majority ruleset,
> even if they aren't, effectively downgrading them to something a bit like
> SPV security without them realising.
>
> A hard fork has multiple desirable properties. Most importantly, it means a
> node can detect it's no longer in the consensus because it'll find its own
> chain height has diverged significantly from its peers. Core already has
> code that knows how to detect this condition and log errors about it as well
> as running the alertnotify script i.e. emailing the admin. Ideally it would
> also stop serving work so miners shut down or fail over, but this is easily
> added to the CheckForkWarningConditions() function.
>
> In other words, this gives the cleanest failure we can give, such that any
> procedures a node operator has put in place to alert them of divergence will
> be triggered.  Any code which is waiting for confirmations will wait forever
> at this point, thus minimising the risk of loss.
>
> Additionally, forcing old peers to fall behind means SPV clients will pick
> the right chain, and not end up downloading transactions or blocks that are
> about to be doomed at the next re-org. They can easily choose to ignore
> transactions relayed by peers that are too far behind and thus not end up
> accepting transactions that are no longer valid according to the majority (a
> scenario which can cause monetary loss).
>
> I don't think hard forks should be scary. Mechanisms are in place to warn
> people and they can be scheduled with plenty of time in advance. The main
> stated justification for a soft fork is backwards compatibility, but in a
> system like Bitcoin you really don't want to be running behind the consensus
> and it's hard to imagine any node operator deliberately choosing to stay on
> the wrong side of the fork. It's not like other software where people can
> choose to skip an upgrade and things still work just like before.
>
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-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/