Jacob Eliosoff via bitcoin-dev
2017-06-09 04:40:57 UTC
Hilliard's BIP91  (or splitprotection , or Segwit2x , which both
use variants of BIP91 activation) and the BIP148 UASF . Some of this is
subtle so CORRECTIONS WELCOME, but my conclusions are:
1. It's extremely unlikely BIP91-type logic can activate segwit in time to
avoid a BIP148 chain split.
2. So, in practice all we can do is ensure the BIP148 split is as painless
REASONING: First, some dates. BIP148, whose deadline is already deployed
and thus unlikely to be postponed, starts orphaning non-segwit blocks on
midnight (GMT) the morning of August 1. Meanwhile, here are Bitcoin's
rough expected next four difficulty adjustment dates (they could vary by
~1-3 days depending on block times, but it's unlikely to matter here):
1. June 17
2. June 30
3. July 13
4. July 27
If Segwit activates on adj date #5 or later (August), it will be too late
to avoid BIP148's split, which will have occurred the moment August began.
So, working backwards, and assuming we want compatibility with old BIP141
- Segwit MUST activate by adj #4 (~July 27)
- Therefore segwit MUST be locked in by adj #3 (~July 13: this is
inflexible, since this logic is in already-deployed BIP141 nodes)
- Therefore, I *think* >50% of hashpower needs to be BIP91 miners,
signaling bit 1 and orphaning non-BIP91 (ie, BIP91's bit 4 must activate),
by adj #2 (June 30)?
- Therefore, as currently designed, BIP91 bit 4 must be locked in by adj #1
- Therefore, >=80% of hashrate must start signaling BIP91's bit 4 by a few
There are ways parts of this could be sped up, eg, James' "rolling
100-block lock-in periods" , to get BIP91 signaling bit 1 sooner. But
to be compatible with old BIP141 nodes, >50% of hashrate must be activated
BIP91 miners by ~June 30: there's no fudging that.
So, it seems to me that to avoid the BIP148 split, one of two things would
have to happen:
a) 95% of hashrate start signaling bit 1 by ~June 30. Given current stat
is 32%, this would basically require magic.
b) BIP91 is deployed and >50% (80% or whatever) of hashrate is *activated*
BIP91 miners by ~June 30, ~3 weeks from now. Again, much too soon.
So, I think the BIP148 split is inevitable. I actually expect that few
parts of the ecosystem will join the fork, so disruption will be bearable.
But anyway let me know any flaws in the reasoning above.