On 10/20/23 9:25 PM, Peter Todd wrote:
On Fri, Oct 20, 2023 at 09:03:49PM -0400, Matt Corallo wrote:
What are anchor outputs used for other than increasing fees?
Because if we've pre-signed the full fee range, there is simply no need for
anchor outputs. Under any circumstance we can broadcast a transaction with a
sufficiently high fee to get mined.
Indeed, that is what anchor outputs are for. Removing the pre-set feerate
solved a number of issues with edge-cases and helped address the
fee-inflation attack. Now, just using pre-signed transactions doesn't have
to re-introduce those issues - as long as the broadcaster gets to pick which
of the possible transactions they broadcast its just another transaction of
theirs.
Still, I'm generally really dubious of the multiple pre-signed transaction
thing, (a) it would mean more fee overhead (not the end of the world for a
force-closure, but it sucks to have all these individual transactions
rolling around and be unable to batch), but more importantly (b) its a bunch
of overhead to keep track of a ton of variants across a sufficiently
granular set of feerates for it to not result in substantially overspending
on fees.
Quite the contrary. Schnorr signatures are 64 bytes, so in situations like
lightning where the transaction form is deterministically derived, signing 100
extra transactions requires just 6400 extra bytes. Even a very slow 100KB/s
connection can transfer that in 64ms; latency will still dominate.
Lightning today isn't all that much data, but multiply it by 100 and we start racking up data enough
that people may start to have to store a really material amount of data for larger nodes and dealing
with that starts to be a much bigger pain then when we're talking about a GiB or twenty.
RBF has a minimum incremental relay fee of 1sat/vByte by default. So if you use
those 100 pre-signed transaction variants to do nothing more than sign every
possible minimum incremental relay, you've covered a range of 1sat/vByte to
100sat/vByte. I believe that is sufficient to get mined for any block in
Bitcoin's entire modern history.
CPFP meanwhile requires two transactions, and thus extra bytes. Other than edge
cases with very large transactions in low-fee environments, there's no
circumstance where CPFP beats RBF.
What I was referring to is that if we have the SIGHASH_SINGLE|ANYONECANPAY we can combine many HTLC
claims into one transaction, vs pre-signing means we're stuck with a ton of individual transactions.
Matt
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