[bitcoin-dev] Straight Flag Day (Height) Taproot Activation

Jeremy jlrubin at mit.edu
Sun Feb 28 19:43:53 UTC 2021

I agree with much of the logic presented by Matt here.

BIP8 was intended to be simpler to agree on to maintain consensus, yet we
find ourselves in a situation where a "tiny" parameter has the potential to
cause great network disruption and confusion (rationality is not too useful
a concept here given differing levels of sophistication and information).
It is therefore much simpler and more likely to be universally understood
by all network participants to just have a flag day. It is easier to
communicate what users should do and when.

This is ultimately not coercive to users because the upgrade for Taproot
itself is provable and analyzable on its own, but activation parameters
based on what % of economically relevant nodes are running an upgrade by a
certain date are not. Selecting these sorts of complicated consensus
parameters may ultimately present more opportunity for a cooptable
consensus process than something more straightforward.

That said, a few points strike me as worth delving into.

1) Con: Mandatory signalling is no different than a flag day. Mandatory
signaling is effectively 2 flag days -- one for the signaling rule, 1 for
the taproot type. The reason for the 2 week gap between flag day for
signaling and flag day for taproot rules is, more or less, so that nodes
who aren't taproot ready at the 1st flag day do not end up SPV mining
(using standardness rules in mempool prevents them from mining an invalid
block on top of a valid tip, but does not ensure the tip is valid).
2) Con: Releasing a flag day without releasing the LOT=true code leading up
to that flag day means that clients would not be fully compatible with an
early activation that could be proposed before the flag day is reached.
E.g., LOT=true is a flag day that retains the possibility of being
compatible with other BIP8 releases without changing software.
3) Pro: BIP-8 is partially in service of "early activation" and . I'm
personally skeptical that early activation is/was ever a good idea. A fixed
activation date may be largely superior for business purposes, software
engineering schedules, etc. I think even with signaling BIP8, it would be
possibly superior to activate rules at a fixed date (or a quantized set of
fixed dates, e.g. guaranteeing at least 3 months but maybe more).
4) Pro: part of the argument for BIP-8=false is that it is possible that
the rule could not activate, if signaling does not occur, providing
additional stopgap against dev collusion and bugs. But BIP-8 can activate
immediately (with start times being proposed 1 month after release?) so we
don't have certainty around how much time there is for that secondary
review process (read -- I think it isn't that valuable) and if there *is* a
deadly bug discovered, we might want to hard-fork to fix it even if it
isn't yet signaled for (e.g., if the rule activates it enables more mining
reward). So I think that it's a healthier mindset to release a with
definite deadline and not rule out having to do a hard fork if there is a
grave issue (we shouldn't ever release a SF if we think this is at all
likely, mind you).
5) Con: It's already taken so long for taproot, the schedule around taproot
was based on the idea it could early activate, 2022 is now too far away. I
don't know how to defray this other than, if your preferred idea is 1 year
flag day, to do that via LOT=true so that taproot can still have early
activation if desired.

Overall I agree with the point that all the contention around LOT, makes a
flag day look not so bad. And something closer to a flag day might not be
so bad either for future forks as well.

However, I think given the appetite for early activation, if a flag day is
desired I think LOT=true is the best option at this time as it allows our
flag day to remain compatible with such an early activation.

I think we can also clearly communicate that LOT=true for Taproot is not a
precedent setting occurence for any future forks (hold me accountable to
not using this as precedent this should I ever advocate for a SF with
similar release parameters).
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