[bitcoin-dev] Why not Child-Pays-For-Parent?

Justus Ranvier justus at openbitcoinprivacyproject.org
Fri Jul 10 17:02:43 UTC 2015

On 07/10/2015 11:31 AM, Jeff Garzik wrote:
> This is a good explanation but it does not address reachability.  TX_a, the
> first tx sent out on the network, presumably has insufficient fee to get
> mined - which also means it did not necessarily even reach all miners.
> Simply sending out TX_b with added fee does not guarantee that nodes
> suddenly have TX_a, which they may have ignored/dropped before.

I'm not sure why that's actually a problem.

CPFP is initiated by the recipient of the parent transaction, and so if
the recipient is creating this transaction in the first place they must
have a copy of the parent transaction which can/should broadcast at the
same time.

If the child reaches a CPFP miner, then presumably the parents made it
as well (any path between the sender and the miner that doesn't relay
the parent should reject the child as trying to spend non-existent
coins), so both of the transactions can be mined at the same time.

Justus Ranvier
Open Bitcoin Privacy Project
justus at openbitcoinprivacyproject.org
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