Quote from: bitcoin2009sw on Today at 03:45:55 PM

Let me explain in detail everything related to transaction replacement, particularly focusing on Replace-by-Fee (RBF) and how it works in the Bitcoin network. I will also cover the process of replacing transactions, the use of RBF, and how to manage transactions in different scenarios.

What is Replace-by-Fee (RBF)?
Replace-by-Fee (RBF) is a feature that allows a user to replace a Bitcoin transaction that has not yet been confirmed by the network with another transaction that pays a higher fee. This can be helpful in case the original transaction was not included in the next block due to low fees, especially in times of network congestion.

When RBF is enabled, the sender can increase the fee and re-broadcast the transaction, increasing the chances of it being included in the next block by miners.

How RBF Works:
Transaction Broadcasting: A user broadcasts a transaction with a specified fee. If the transaction is not confirmed (due to low fees or network congestion), the user can replace the original transaction with one that has a higher fee.
RBF-Compatible Transactions: Transactions that are sent with RBF enabled are considered "RBF transactions". These transactions have a special flag in their structure that allows them to be replaced.
Why Replace a Transaction?: If a user sends a transaction with low fees and it’s stuck in the mempool (not confirmed), they can increase the fee to make the transaction more attractive to miners. Miners prioritize transactions with higher fees.
How to Create and Replace Transactions with RBF:
1. Creating a Transaction with RBF Enabled:
To send a transaction with RBF enabled, the wallet or software you are using must support RBF. Most modern Bitcoin wallets, including Bitcoin Core, allow you to enable or disable RBF when creating transactions.

Steps in Bitcoin Core (GUI):
Open Bitcoin Core and go to the Send tab.
Select the address to send the Bitcoin to and enter the amount.
If RBF is available, you can check a box or select an option to enable Replace-by-Fee. This flag ensures that the transaction can be replaced with a higher fee later.
Sign and broadcast the transaction.
Steps in Bitcoin Core (Command Line):
You can also use Bitcoin Core’s command-line interface to create an RBF-enabled transaction.

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bitcoin-cli createrawtransaction '[{"txid":"previous_txid","vout":0}]' '{"recipient_address":amount}'
To enable RBF, you can use the following command:

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bitcoin-cli sendtoaddress "recipient_address" amount "" "" true
Here, the true value at the end enables RBF for this transaction.

2. Replacing a Transaction:
If the transaction you sent was not confirmed due to low fees, you can replace it with a new transaction that has a higher fee. This is where RBF comes into play.

Steps to Replace a Transaction:
Identify the transaction: You need the Transaction ID (TXID) of the original transaction that is stuck.
Create a new transaction: Use the same inputs (unspent transaction outputs, UTXOs) as the original transaction, but increase the fee.
Rebroadcast the transaction: Once the new transaction is created and signed, rebroadcast it to the network. Since it has a higher fee, it will be more attractive to miners and is likely to be confirmed faster.
3. Using Bitcoin Core Command Line to Replace:
You can use the following command to replace a transaction using RBF:

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bitcoin-cli walletcreatefundedpsbt '[{"txid":"previous_txid","vout":0}]' '{"recipient_address":amount}' 0 false
The false option ensures that RBF is not enabled. You can set true if you want to enable RBF during the creation of this transaction.
After creating the transaction, sign and broadcast it to the Bitcoin network.
4. How to Replace an Unconfirmed Transaction:
If you are using a wallet that supports RBF, you can also replace a transaction using the wallet’s interface or an API. Some wallets will automatically allow you to increase the fee of an unconfirmed transaction directly from their UI (like Electrum).

What Happens if the Transaction Doesn't Support RBF?
If a transaction is not RBF-enabled, it cannot be replaced once broadcast to the network. The transaction is considered final once it's broadcast, and the only option is to wait for it to be confirmed or rejected by the network.

Non-RBF transactions cannot be modified or replaced.
Once a non-RBF transaction is broadcast, it is essentially locked in place, and only the miners can choose whether or not to include it in a block.
How to Check if a Transaction Supports RBF?
You can check if a transaction is replaceable by looking at the raw transaction data or by querying the Bitcoin node or blockchain explorer.

In Bitcoin Core: You can use the command getrawtransaction to check whether the transaction supports RBF. If the transaction contains the "replaceable" flag, it is replaceable.
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bitcoin-cli getrawtransaction "TXID" 1
Blockchain Explorer: Many blockchain explorers show whether a transaction is RBF-enabled. You can check the status of the transaction by entering its TXID into the explorer.
Example Scenario:
Let’s say you send a transaction with a low fee and it doesn't get confirmed after several blocks. In this case:

You check the status of your transaction using a blockchain explorer.
If the transaction is still in the mempool (unconfirmed), you can create a new transaction that replaces the original transaction with a higher fee (thanks to RBF).
You broadcast the new transaction, and since it pays a higher fee, miners are more likely to confirm it.
Why Use Replace-by-Fee?
Speed Up Transaction Confirmation: If your transaction is stuck due to low fees, RBF allows you to increase the fee and get it confirmed faster.
Network Congestion: In times of high network traffic, RBF gives you a way to "boost" your transaction's priority by increasing the fee, ensuring it doesn’t stay stuck.
Avoid Stuck Transactions: For users who want more control over their transaction's confirmation, RBF provides the flexibility to adjust the fees dynamically.
Summary:
RBF (Replace-by-Fee) allows you to replace an unconfirmed transaction with a higher-fee transaction.
Enable RBF during the creation of a transaction in compatible wallets like Bitcoin Core.
Replace transactions with higher fees if they are stuck in the mempool.
Non-RBF transactions cannot be replaced once broadcast to the network.
Check if a transaction supports RBF using raw transaction data or a blockchain explorer.
RBF provides flexibility for users to manage their transactions and avoid delays caused by network congestion.

Your choice for enable or not RBf in tx ended
Each n every tx you send to mempool, by default set RBf enabled at minners (mempool)
Read Bitcoin core current rules