Bitcoin Forum

UPDATE: These are all CPFP... mystery solved.

Reference: https://github.com/brianddk/btc-small-fee (https://github.com/brianddk/btc-small-fee)

There has recently been a number of very good analysis tools / sites related to fee calculation based on mempool fee distribution.  I began to get more interested in fee distribution on confirmed blocks instead.  I believe both pursuits are important.  One gives info on what the competition is while the other gives info on what the last selection process was.  What I've found is that all blocks seem to include... for lack of a better term... charitable transactions.  I'm trying to understand why.  If there is an abundance of fair fee transactions in the mempool, why would a miner include anything else.  The best WAG I can come up with, are the following:

• Off-book incentive - Perhaps the miners have an off-book incentive to include some transactions that further their business.  Some payment to another pool or their utility company or whatever.  Perhaps the transaction is low-priority as far as the miners are concerned, so they include some fee in case some other miner finds it, but really they are just waiting to pick up those transactions themselves.
  
• Too busy to care - Perhaps the compute cost to actually filter out the transactions is higher than the benefit of excluding them.  To me this is the most likely.  There are good ways to do a sloppy sort that would get a selection mostly sorted, but not entirely.  I'd imagine a bubble-sort continually running on the mempool, but blocks periodically getting cut before the sort is complete.
  
• Child-pays-for-parent - Perhaps these low fee transactions are CPFP transactions, and there is a high-fee child somewhere in the block.  I'll need to modify my block-walker to try to flesh this-possibility out.
  
• A perfect fit - Perhaps the size of the transaction is perfect to allow the block to be at maximum capacity.  For example, if there were 191 bytes space left in the block, it is obviously more profitable to include a low-fee 191 byte transaction, than to just leave that space blank.
  
• Something I don't know - I accounted for SegWit, and admittedly did not account for CPFP.  Perhaps there is another part of the protocol that makes these TXNs profitable that I failed to consider
  

sz	fee	segwit	tx.hash
224	4480	false	1aebfb469ce0aac91e13b47ea6e6cbdab54152d4edebdc282d1b064ee605edf6 (https://blockchain.info/tx/1aebfb469ce0aac91e13b47ea6e6cbdab54152d4edebdc282d1b064ee605edf6)
226	4520	false	ff324af8cb7a74006f55a1300a6833ae4a362477e894e25e2a604b45909f5ae9 (https://blockchain.info/tx/ff324af8cb7a74006f55a1300a6833ae4a362477e894e25e2a604b45909f5ae9)
215	8357	true	99984dc2694fceaac51067be155508a32916d8e32c07ebee30722521c3f8d815 (https://blockchain.info/tx/99984dc2694fceaac51067be155508a32916d8e32c07ebee30722521c3f8d815)
226	10000	false	d2df5a3c1f743f9375df0b355b26a37f98a4522e6ad9560a26bb7d84ae956bcc (https://blockchain.info/tx/d2df5a3c1f743f9375df0b355b26a37f98a4522e6ad9560a26bb7d84ae956bcc)
225	11300	false	473fa22f9e882aef5edb81a07fb6b57bfc8c5c3b57716e0be76e843796ac1be8 (https://blockchain.info/tx/473fa22f9e882aef5edb81a07fb6b57bfc8c5c3b57716e0be76e843796ac1be8)
226	2260	false	0a21c097f0c59d9a52df9fb565e59f504a7a577b9a7289bfb892cd68d5f58c11 (https://blockchain.info/tx/0a21c097f0c59d9a52df9fb565e59f504a7a577b9a7289bfb892cd68d5f58c11)
225	3616	false	7ad533320fd0394fae388c62de0f416dad865154d43360550b03fba354b01a3a (https://blockchain.info/tx/7ad533320fd0394fae388c62de0f416dad865154d43360550b03fba354b01a3a)
191	3840	false	8687f155056110717d327d0ee5f33153f7684976a095d67d35a271461e37b078 (https://blockchain.info/tx/8687f155056110717d327d0ee5f33153f7684976a095d67d35a271461e37b078)
225	4972	false	c04d4c27dcc93623b00fca37e6bbfd8c4949fc1d9197a2724fbd5f399fb5ce8e (https://blockchain.info/tx/c04d4c27dcc93623b00fca37e6bbfd8c4949fc1d9197a2724fbd5f399fb5ce8e)
373	5610	false	bf632f070df0c1d9c849a20f165143fbb07d5c6829e83cb2afecddbda659fd17 (https://blockchain.info/tx/bf632f070df0c1d9c849a20f165143fbb07d5c6829e83cb2afecddbda659fd17)
224	5625	false	2ec6e58d2bf4ff2928208ca564b5597b1a7ff93b291a4793f9d3028f003f8fe1 (https://blockchain.info/tx/2ec6e58d2bf4ff2928208ca564b5597b1a7ff93b291a4793f9d3028f003f8fe1)
225	5675	false	11b2e7c3a0b42695dd47461b1383807dd0fa74aaf83ae11ddf04b289b028dc2b (https://blockchain.info/tx/11b2e7c3a0b42695dd47461b1383807dd0fa74aaf83ae11ddf04b289b028dc2b)
374	9400	false	e81c1859b48414e8f0a192d1c90b9a6c3fc4a3c0f9877ab1e9fb21e143851f35 (https://blockchain.info/tx/e81c1859b48414e8f0a192d1c90b9a6c3fc4a3c0f9877ab1e9fb21e143851f35)
226	11692	false	f8664ca547b4254bed5a4ca48c5e022af2297f7ac2fc42db0fc9d70fa7481839 (https://blockchain.info/tx/f8664ca547b4254bed5a4ca48c5e022af2297f7ac2fc42db0fc9d70fa7481839)
226	24300	false	2799a4d60f87a380e3b56b9e142fb8113e14bc6e9b4b192d65f5a9a00b04b66e (https://blockchain.info/tx/2799a4d60f87a380e3b56b9e142fb8113e14bc6e9b4b192d65f5a9a00b04b66e)