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. On Fri, Jul 10, 2015 at 12:28 PM, Tier Nolan <tier.no...@gmail.com> wrote: > > > On Fri, Jul 10, 2015 at 5:09 PM, Richard Moore <m...@ricmoo.com> wrote: > >> I was also wondering, with CPFP, should the transaction fee be based on >> total transactions size, or the sum of each transaction’s required fee? For >> example, a third transaction C whose unconfirmed utxo from transaction B >> has an unconfirmed utxo in transaction A (all of A’s inputs are confirmed), >> with each A, B and C being ~300bytes, should C’s transaction fee be 0.0001 >> btc for the ~1kb it is about to commit to the blockchain, or 0.0003 btc for >> the 3 transactions it is going to commit. >> > > It should be whatever gives the highest fee. In effect, child pays for > parent creates compound transactions. > > A: 250 bytes, 0 fee > B: 300 bytes: 0.0005 fee > C: 400 bytes: 0.0001 fee > > There are 3 combinations to consider > > A: 0 fee for 250 bytes = 0 per byte > A&B: 0.0005 fee for 550 bytes = 0.91 uBTC per byte > A&B&C: 0.0006 fee for 950 bytes = 0.63uBTC per byte > > This means that the A&B combination has the best fee per byte value. A&B > should be added to the memory pool (if 0.91 uBTC per byte is above the > threshold). > > Once A&B are added, then C can be reconsidered on its own. > > C: 0.0001 for 400 bytes = 0.25 BTC per byte > > If that is above the threshold, then C should be added. > > In practice, it isn't possible to check every combination. If there are N > transactions, then checking all triple combinations costs around N cubed. > > A 2 pass system could get a reasonably efficient result. > > B is 0.0005 fee for 300 bytes = 1.67 uBTC per byte and is assumed to be a > high value transaction. > > The algorithm would be > > Pass 1: > Process all transactions in order of BTC per byte, until block is full > If the transaction's parents are either already in the pool or a > previous block, add the transaction. > > Pass 1: > Process all non-included transactions in order of BTC per byte, until > block is full > If the transaction's parents are either already in the pool or a > previous block, add the transaction. > > Otherwise, consider the transaction plus all non-included ancestors as > a single transaction > If this combined transaction has a higher BTC per byte than the > lowest transaction(s), > add the combined transaction > drop the other transaction(s) > > > > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > >
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