Cluster Mempool RBF Thoughts

[instagibbs]

@sdaftuar

Issue 3: In the new cluster mempool world, the feerate diagram might be satisfied for a transaction package (A, B), but fail to relay successfully if A is valid in a peer’s mempool and then B’s RBF attempt is validated using feerate diagram rules (which can fail because the starting diagram for a peer might include tx A).

Seems like per-chunk processing allows for a mild “parent pays for child RBF”. The “cost” of doing per-chunk evaluation: people may be making cpfp chains one by one, and this will not be in lock-step with a whole package being gossiped at once. #26711-like solutions mean you get less of this asymmetry, at increased cost of complexity, and not always dealing with chunks.