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Comment by gomox | Hacker News Reader

Most wallets allow you get out of this situation with a clever feature.

What you do is raise the insufficient fee after the fact by issuing a new transaction that is dependent on the first one, and adding a large enough fee to the second one. This is known as "child pays for parent" in BTC lingo.

That being said, the fee for a good transaction now is around $22 so it might not be worth doing for your $50 send.

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Unfortunately in a child pays for parent scenario you need to pay double fees. Otherwise it's not worthwhile for the miner to confirm both transactions in order to only get one fee. So they'd need to pay $44 in fees in order to free their $50.

The miner only needs to confirm the replacement transaction as the parent will get purged from the mempool. There’s still only one transaction recorded on the blockchain.

Wouldn't it be simpler to send another transaction with identical inputs, but with a higher fee? I haven't tested this, but I'd expect it to replace the old (conflicting) transaction in the mempool.

I think if you just naively did that, you would risk the funds being spent twice if both transactions are included in the block (unlikely, but possible).

There is an implementation of essentially the same concept that you are describing called "replace by fee". I haven't seen it implemented in any wallet software, but apparently it's in Bitcoin Core.

I think the tricky part is getting nodes to relay transactions that can look like double spending.

It's not possible for a valid block to include multiple transactions spending the same input. All full nodes will reject such a block as invalid.

Thanks, I didn't know that.

This is exactly how replace by fee works. If you use the same inputs, only one of the transactions can be included. The reason it's called replace by fee is that unlike Satoshi's original design for transaction replacement, which he disabled because it could be abused to waste node resources for free by repeatedly replacing transactions, it requires a higher fee for each replacement to discourage abuse. (Bitcoin Cash subsequently removed replace by fee out of some weird belief it was an attack on Satoshi's vision; this was of course nonsense, since he specifically designed transactions to be replaceable. It was also pointless, since it's a voluntary miner policy rather than a consensus rule and there's economic incentive for them to support it.)

If your fee was so low that it has not cleared in many days then it is probably not being included in any blocks. Especially in a time like now when fees are increasing, putting in another identical transaction with a high enough fee to get confirmed should work fine. I'm not sure how your wallet software will deal with it though.

Where does this $22 go? What hard ware do I need to set up my own machine to process these transactions and get the fees to keep?

All fees go to the person who mines the next block, so in order to guarantee you get the fees, you need a mining machine that wins every time (in which case you'd be in control of way more than just the fees). Basically, you can't.

Transaction fees go to the miners. Lookup Bitcoin mining.

You'll probably find it's not worth it...

You're still paying a huge fee, though.

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