Ephemeral Anchors and MEVil

[instagibbs]

@instagibbs

This was what I was thinking, I wasn’t sure of this, since the proposed spend could also be replacing other in-mempool transactions. Could conflicting with other transactions somehow cause this check to be insufficient from incentives perspective?

I think not doing a full diagram check means it would be insufficient to stop incentives to inflate the value.

For math simplicity, assume an additional input to doublepend TxC is 65 vbytes:

flowchart TD
    A[TxA: fee 0\nsize 300\n10000 sats in anchor] --> B[TxB: fee 11780\nsize 130]
    C[TxC: fee 10000\nsize 384\n conf with TxB]

TxA+PureBurn(10k sats) package rate is 27 sat/vbyte
TxA+TxB package rate is the same
But it also pays for eviction of TxC. In other words, a channel counterparty has additional incentives to drive it up.

If we actually require a diagram check, it may be that we “simulate” the conflict more directly in an actual implementation and let RBF logic handle it post-cluster mempool.

Pre-cluster mempool, it may be simpler to just start with 0-value outputs.