Re: [bitcoin-dev] Barry Silbert segwit agreement

[James Hilliard <james.hilliard1@gmail.com>]

Mandatory signalling is the only way to lock in segwit with less than
95% hashpower without a full redeployment(which for a number of
technical reasons isn't feasible until after the existing segwit
deployment expires). There's no reason not to signal BIP141 bit 1
while also signalling bit 4, but you would want to use bit 4 to
coordinate bit 1 mandatory signalling.

It would not be feasible to schedule any HF until one can be
completely sure BIP141 is active(at least not without waiting for the
timeout and doing a redeployment) due to activation/p2p codepath
complexity. This is why the mandatory signalling period is needed.

Since it is likely a HF will take months of development and testing I
see this or something similar as the fastest safe path forward:
1. Use BIP91 or similar to activate BIP141 via mandatory signalling
ASAP(likely using bit 4)
2. Develop HF code based on assumption that BIP141 is active so that
you only have to test the BIP141->HF upgrade/activation codepath.
3. Deploy HF after BIP141 lock in(bit 4 can be reused again here since
this will be after BIP91 expiration)

When rolling out some features it often makes sense to combine them
into a single fork for example BIP's 68, 112, 113 were rolled out at
the same time as are BIP's 141, 143, 144, 145 for segwit, however a HF
has required features that would conflict with with features in the
segwit rollout which is why attempting to simultaneously deploy them
would cause major complexity/testing issues(you would have to deal
with feature conflict resolution for multiple potential activation
scenarios). By doing a staged rollout of segwit and then a HF you get
a single testable upgrade path.

Based on past development experiences I wouldn't expect a 6 month
timeline to be realistic for a properly tested HF, but this proposed
upgrade path should be the fastest available for both SegWit and a HF
regardless.

On Fri, May 26, 2017 at 4:10 PM, Jacob Eliosoff via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> Just to clarify one thing, what I described differs from BIP91 in that
> there's no orphaning.  Just when Segwit2MB support reaches 80%, those 80%
> join everyone else in signaling for BIP141.  BIP91 orphaning is an optional
> addition but my guess is it wouldn't be needed.
>
>
> On May 26, 2017 4:02 PM, "Matt Corallo" <lf-lists@mattcorallo.com> wrote:
>>
>> Your proposal seems to be simply BIP 91 tied to the
>> as-yet-entirely-undefined hard fork Barry et al proposed.
>>
>> Using James' BIP 91 instead of the Barry-bit-4/5/whatever proposal, as
>> you propose, would make the deployment on the incredibly short timeline
>> Barry et al proposed slightly more realistic, though I would expect to
>> see hard fork code readily available and well-tested at this point in
>> order to meet that timeline.
>>
>> Ultimately, due to their aggressive timeline, the Barry et al proposal
>> is incredibly unlikely to meet the requirements of a
>> multi-billion-dollar system, and continued research into meeting the
>> spirit, not the text, of their agreement seems warranted.
>>
>> Matt
>>
>> On 05/26/17 17:47, Jacob Eliosoff via bitcoin-dev wrote:
>> > Forgive me if this is a dumb question.  Suppose that rather than
>> > directly activating segwit, the Silbert/NYC Segwit2MB proposal's lock-in
>> > just triggered BIP141 signaling (plus later HF).  Would that avoid
>> > incompatibility with existing BIP141 nodes, and get segwit activated
>> > sooner?  Eg:
>> >
>> > - Bit 4 (or bit 5 or whatever, now that BIP91 uses 4) signals support
>> > for "segwit now, HF (TBD) at scheduled date (Nov 23?)"
>> > - If bit 4 support reaches 80%, it locks in two things: the scheduled HF
>> > (conditional on segwit), and *immediately* turning on bit 1 (BIP141
>> > support)
>> >
>> > I realize this would still leave problems like the aggressive HF
>> > schedule, possible chain split at the HF date between Segwit2MB nodes
>> > and any remaining BIP141 nodes, etc.  My focus here is how
>> > incompatibility with existing nodes could be minimized.
>> >
>> > (BIP91 could also be used if BIP141 support still fell short of 95%.
>> > But if Segwit2MB support reaches 80%, it seems likely that an additional
>> > 15% will support BIP141-without-HF.)
>> >
>> >
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>> >
>
>
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