Resolving the “Replacement Transaction Underpriced” Error in Ethereum

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Ethereum, a leading blockchain platform, often presents developers with intricate challenges. One such challenge is the "Replacement Transaction Underpriced" error. This article aims to provide a comprehensive understanding of this error and offers solutions to address it.

graph TD A[Start] --> B[Initiate Transaction] B --> C{Pending Transaction?} C -->|Yes| D[Replace Transaction] D --> E[Set Gas Price 10% Higher] E --> F[End] C -->|No| G[Send New Transaction] G --> H[Adjust Nonce] H --> F

What Triggers the Error?

The "Replacement Transaction Underpriced" error typically arises when:

  1. A new transaction is being sent after all previous transactions have been completed.
  2. There's an attempt to replace a pending (unmined) transaction with a new raw transaction.

Addressing the Error

Sending a New Transaction

The error message suggests that the system perceives an attempt to replace a pending transaction. This perception arises when the raw transaction being sent shares the same nonce as another transaction that's still pending.

Solution: To circumvent this, simply adjust the nonce to a value one higher than the last pending transaction. It's crucial to manage this internally, rather than solely depending on web3.eth.getTransactionCount().

Replacing a Pending Transaction

The 10% Minimum Rule

When the objective is to replace a transaction that's still pending, it's essential to persuade the miners to prioritize the new transaction. This can be achieved by setting a gas price that's at least 10% higher than the gas price of the pending transaction.

For instance, if using web3:

JavaScript
const gasPrice = web3.eth.gasPrice.toNumber() * 1.40;

It's worth noting that the above code inflates the web3.eth.gasPrice by 40%. This might not always be 10% higher than the pending transaction's gas price, especially since web3.eth.gasPrice can fluctuate.

Determining the Minimum Gas Price

If the hash of the pending transaction is available, the requisite gas price can be ascertained using:

JavaScript
replacement_price = web3.eth.getTransaction(pending_txn_hash).gasPrice * 1.101;

This calculation involves floating point math, which can introduce rounding errors. Hence, an additional 10th of a percent is added to ensure the result exceeds the minimum.

FAQs

  • What does the "Replacement Transaction Underpriced" error mean?
    • It indicates an attempt to replace a pending transaction with a new one that has the same nonce.
  • How can I avoid this error?
    • Ensure that the nonce for a new transaction is one higher than the last pending transaction. If replacing a transaction, set a gas price at least 10% higher than the pending transaction.
  • Why is the 10% rule important?
    • It persuades miners to prioritize the new transaction over the pending one.

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