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From: Rusty Russell <rusty@rustcorp.com.au>
To: Matt Corallo <lf-lists@mattcorallo.com>,
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Cc: lightning-dev@lists.linuxfoundation.org
Subject: Re: [bitcoin-dev] [Lightning-dev] CPFP Carve-Out for Fee-Prediction
Issues in Contracting Applications (eg Lightning)
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Matt Corallo <lf-lists@mattcorallo.com> writes:
> As an alternative proposal, at various points there have been
> discussions around solving the "RBF-pinning" problem by allowing
> transactors to mark their transactions as "likely-to-be-RBF'ed", which
> could enable a relay policy where children of such transactions would be
> rejected unless the resulting package would be "near the top of the
> mempool". This would theoretically imply such attacks are not possible
> to pull off consistently, as any "transaction-delaying" channel
> participant will have to place the package containing A at an effective
> feerate which makes confirmation to occur soon with some likelihood. It
> is, however, possible to pull off this attack with low probability in
> case of feerate spikes right after broadcast.
I like this idea.
Firstly, it's incentive-compatible[1]: assuming blocks are full, miners
should always take a higher feerate tx if that tx would be in the
current block and the replaced txs would not.[2]
Secondly, it reduces the problem that the current lightning proposal
adds to the UTXO set with two anyone-can-spend txs for 1000 satoshis,
which might be too small to cleanup later. This rule would allow a
simple single P2WSH(OP_TRUE) output, or, with IsStandard changed,
a literal OP_TRUE.
> Note that this clearly relies on some form of package relay, which comes
> with its own challenges, but I'll start a separate thread on that.
Could be done client-side, right? Do a quick check if this is above 250
satoshi per kweight but below minrelayfee, put it in a side-cache with a
60 second timeout sweep. If something comes in which depends on it
which is above minrelayfee, then process them as a pair[3].
Cheers,
Rusty.
[1] Miners have generally been happy with Defaults Which Are Good For The
Network, but I feel a long term development aim should to be reduce
such cases to smaller and smaller corners.
[2] The actual condition is subtler, but this is a clear subset AFAICT.
[3] For Lightning, we don't care about child-pays-for-grandparent etc.
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