General things you need to know (as both receiver and sender):
1) A common novice mistake about fee:
Fee is calculated based on “size in bytes” not “size as in amount” which means it doesn’t matter if you send 10BTC or 0.01BTC as far as fees are concerned. If you have are spending many outputs and create multiple new outputs the size of your transaction in bytes will be high and you have to pay higher fee.
2) A very important thing to know
Transaction can be reversed until it is confrimed. in other words you do not own the received bitcoins until the transaction has at least 1 confirmation.
- If you run a full node and in normal network status: 3 confirmation is Highly reliable
- If you are running an SPV wallet: 6 confirmation is Highly reliable
- In case of emergencies 30 confirmation is suggested (this is not common) More information here
3) Ask a miner directly to mine your transaction, this may not be free.
You can use ViaBTC accelerator tool. Read the details on the ViaBTC website.
If nothing else worked, you can contact Quickseller (Please include your transaction ID when contacting Quickseller to speed up the process) which does it as a volunteer work. He will then ask you to
– Confirm the transaction is not any kind of double spend, or attempt to harm any entity
– Pay a fee to f2pool payout address
He can then push your transaction to f2pool and the next block that f2pool mines will include your transaction.
Things to do as sender:
1) Pay Appropriate amount of fees!
New versions of most wallets have dynamic fees based on current status of mempool and previous blocks’ fees and they suggest an appropriate amount of fee automatically based on your transaction size and an estimate of how fast it will be confirmed. you can also use a tool like http://bitcoinfees.21.co/ to see what an appropriate fee/byte currently is.
Opt-in Replace-by-fee allows you to replace your previous transaction that had lower fees with a new one that has a higher amount of fee. To put simple when you initially send a transaction with Opt-in RBF, you are telling the network that you may resend the same transaction with higher fees.
In the end it depends on the miners who mine the next block and whether or not they support opt-in RBF.
3) Double Spend.
Double spending is spending the same outputs, and in case your transaction didn’t have enough fees and it wasn’t and RBF transaction the only other way is to double spend and include higher fees.
The problem with this method is that most nodes will see the double spend and not accept or relay the transaction.
Either wait for the transaction to fall out of the mempool (be forgotten) or if you run a full node such as bitcoin core abandon the transaction and start a new one.
Things to do as receiver:
1) Contact the sender
Ask the sender to do one of the above suggestions to speed up the process. Generally ask them to include higher fees.
Child Pays For Parent means the receiver spends an unconfirmed transaction output and includes enough fee covering the first (unconfirmed output) and the new (his own transaction).
This can only be done If your wallets allows spending unconfirmed transactions (it can still be done by creating a transaction manually and then signing it with your wallet)
Not all miners support CPFP
Advanced technical details (BIP125)