A Guide to Bitcoin BTC Transaction Resending (Opt-In Replace-by-Fee)

Introduction

When your Bitcoin transaction remains unconfirmed due to low fees—yet未被节点抛弃—you may need to resend it. Transaction resending essentially replaces your pending transaction in the mempool with a new version.

Three Methods for BTC Transaction Resending

1. Opt-In Replace-by-Fee (RBF)

   • Submits a new transaction with higher fees.
   • Compliant with BIP125.

2. Child Pays for Parent (CPFP)

   • Uses unconfirmed transaction outputs with higher fees.
   • Nodes must bundle the low-fee parent transaction to process the child.

3. Double Spending

   • Creates a conflicting transaction on nodes unaware of the original.
   • Risky and inefficient; use as a last resort.

Comparison of Methods

| Method | Cost Efficiency | Node Support Required | Success Rate |
|----------------|----------------|----------------------|-------------|
| RBF | High | BIP125-enabled | High |
| CPFP | Moderate | None | Moderate |
| Double Spending| Low | None | Low |

Key Takeaways:

• RBF is cheaper than CPFP.
• CPFP works without BIP125 support.
• Double spending is unreliable.

Step-by-Step Guide to Opt-In RBF

Prerequisites

1. Declare Replaceability

   • Explicit: Set at least one input’s nSequence to <0xffffffff-1.
   • Implicit: Inherited if unconfirmed parent transactions are replaceable.

2. Implementation Rules (Bitcoin Core 0.12.0+)

   • No new, unconfirmed inputs in the replacement transaction.
   • Replacement fee must exceed the original fee and the node’s minrelayfee.
   • ≤100 child transactions dependent on the original.

Testing Scenarios

1. Failure Case: Lowering fees (should fail).
2. Success Case: Slightly increased fees (should succeed).
3. Edge Case: Fees exceeding change UTXO (introduces new UTXO; should succeed).

ETH Transaction Resending

Ethereum simplifies resending:

• Submit a new transaction with the same nonce and higher gas fee.
• Miners prioritize the higher-fee version.

FAQ

Q1: Can I use RBF if my wallet doesn’t support BIP125?
A1: No—both sender and nodes must enable BIP125 for RBF.

Q2: Why does CPFP require more fees than RBF?
A2: CPFP involves an additional transaction, doubling fee costs.

Q3: Is double spending illegal?
A3: While technically possible, it violates network trust and is discouraged.

👉 Learn advanced BTC fee strategies

👉 Optimize your ETH gas fees

Note: Always ensure compliance with local regulations when executing blockchain transactions.