In the thread "Revisting BIP 125 RBF policy" @ https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-February/015717.html and https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-March/015797.html I propose replacing rule 3 with a rule that instead demands that the replacement package fee rate exceeds the package fee rate of the original transactions, and that there is an absolute fee bump of the particular transaction being replaced that covers the min-fee rate times the size of the mempool churn's data size.

Perhaps this would address your issue too Rusty.

On Sun, May 20, 2018 at 11:44 PM, Rusty Russell via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
Jim Posen <jim.posen@gmail.com> writes:
> I believe OP_CSV with a relative locktime of 0 could be used to enforce RBF
> on the spending tx?

Marco points out that if the parent is RBF, this child inherits it, so
we're actually good here.

However, Matt Corallo points out that you can block RBF will a
large-but-lowball tx, as BIP 125 points out:

   will be replaced by a new transaction...:

   3. The replacement transaction pays an absolute fee of at least the sum
      paid by the original transactions.

I understand implementing a single mempool requires these kind of
up-front decisions on which tx is "better", but I wonder about the
consequences of dropping this heuristic?  Peter?

Thanks!
Rusty.
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