V3 transaction policy for anti-pinning

[nettimel]

@harding

However, it’s easy to turn those rules into consensus rules: a block may only include a parent ephemeral anchor if it also includes the child spend. We could also add an extra rule in the soft fork: the child spend must include at least two inputs. That would mean the amount of block space used by someone paying miners out-of-band would be equal to the (best and expected normal case) of someone paying any miner in a decentralized fashion. In other words, the incentive for paying out of band would be eliminated.

But as per Peter Todd’s tweet miners can just efficiently spend all the anchor channel outputs together in a block. More efficient than any normal CPFP. It’s still more efficient to pay out of band too because UTXOs for the ephemeral txs need to be created and spent. Vast majority of channels will be stuff like Phoenix in the future, which want one UTXO per user. Can’t anchor that.