On Mon, May 21, 2018 at 01:14:06PM +0930, Rusty Russell via bitcoin-dev 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?

We've discussed this before: that rule prevents bandwidth usage DoS attacks on
the mempool; it's not a "heuristic". If you drop it, an attacker can repeatedly
broadcast and replace a series of transactions to use up tx relay bandwidth for
significantly lower cost than otherwise.

Though these days with relatively high minimum fees that may not matter.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org