I could be wrong, but the latest BIP91 implementation (also included in Segwit2x) cuts the activation period to 336 blocks (2.33 days).  (This has been updated at https://github.com/bitcoin/bips/blob/master/bip-0091.mediawiki.)  So if 80% of hashpower is actually running that code and signaling on bit 4 by July 25 or so, then those 80+% will start orphaning non-bit-1 blocks before Aug 1, and we avoid a split.

There may still be a few non-bit-1 blocks that get orphaned after Aug 1, because they're mined by old BIP141 nodes.  But it seems like very few miners won't be signaling either Segwit2x *or* BIP141 by then...

Make sense?


On Tue, Jun 20, 2017 at 6:48 PM, Mark Friedenbach <mark@friedenbach.org> wrote:
Why do you say activation by August 1st is likely? That would require an entire difficulty adjustment period with >=95% bit1 signaling. That seems a tall order to organize in the scant few weeks remaining. 

On Jun 20, 2017, at 3:29 PM, Jacob Eliosoff via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

If segwit is activated before Aug 1, as now seems likely, there will be no split that day.  But if activation is via Segwit2x (also likely), and at least some nodes do & some don't follow through with the HF 3mo later (again, likely), agreed w/ Greg that *then* we'll see a split - probably in Sep/Oct.  How those two chains will match up and how the split will play out is anyone's guess...



On Jun 20, 2017 6:16 PM, "Hampus Sjöberg via bitcoin-dev" <bitcoin-dev@lists.linuxfoundation.org> wrote:
> Ironically, it looks like most of the segwit2x signaling miners are
> faking it (because they're not signaling segwit which it requires).
> It'll be unfortunate if some aren't faking it and start orphaning
> their own blocks because they are failing to signal segwit.

Well, they're doing some kind of "pre-signaling" in the coinbase at the moment, because the segwit2x project is still in alpha-phase according to the timeline. They're just showing commitment.
I'm sure they will begin signaling on version bit 4/BIP91 as well as actually running a segwit2x node when the time comes.


> As far as prevent a chain split goes, all those things
> (148/91/segwit2x(per today)) effectively guarantee a chainsplit-- so I
> don't think that holds.

Segwit2x/BIP91/BIP148 will orphan miners that do not run a Segwit2x (or BIP148) node, because they wouldn't have the new consensus rule of requiring all blocks to signal for segwit.
I don't believe there would be any long lasting chainsplit though (because of the ~80% hashrate support on segwit2x), perhaps 2-3 blocks if we get unlucky.

Hampus

2017-06-20 23:49 GMT+02:00 Gregory Maxwell via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>:
On Tue, Jun 20, 2017 at 3:44 PM, Erik Aronesty via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> Because a large percentage of miners are indifferent, right now miners have
> to choose between BIP148 and Segwit2x if they want to activate Segwit.

Miners can simply continuing signaling segwit, which will leave them
at least soft-fork compatible with BIP148 and BIP91 (and god knows
what "segwit2x" is since they keep changing the actual definition and
do not have a specification; but last I saw the near-term behavior the
same as BIP91 but with a radically reduced activation window, so the
story would be the same there in the near term).

Ironically, it looks like most of the segwit2x signaling miners are
faking it (because they're not signaling segwit which it requires).
It'll be unfortunate if some aren't faking it and start orphaning
their own blocks because they are failing to signal segwit.

I don't think the rejection of segwit2x from Bitcoin's developers
could be any more resolute than what we've already seen:
https://en.bitcoin.it/wiki/Segwit_support

On Tue, Jun 20, 2017 at 5:22 PM, Mark Friedenbach via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> I think it is very naïve to assume that any shift would be temporary.
> We have a hard enough time getting miners to proactively upgrade to
> recent versions of the reference bitcoin daemon. If miners interpret
> the situation as being forced to run non-reference software in order
> to prevent a chain split because a lack of support from Bitcoin Core,
> that could be a one-way street.

I think this is somewhat naive and sounds a lot like the repeat of the
previously debunked "XT" and "Classic" hysteria.

There is a reason that segwit2x is pretty much unanimously rejected by
the technical community.  And just like with XT/Classic/Unlimited
you'll continue to see a strong correlation with people who are
unwilling and unable to keep updating the software at an acceptable
level of quality-- esp. because the very founding on their fork is
predicated on discarding those properties.

If miners want to go off and create an altcoin-- welp, thats something
they can always do,  and nothing about that will force anyone to go
along with it.

As far as prevent a chain split goes, all those things
(148/91/segwit2x(per today)) effectively guarantee a chainsplit-- so I
don't think that holds.
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