Ethereum: Debug.log : How do I analyze an orphaned transaction?

Analyzing Orphaned Transactions in Ethereum

Orphaned transactions are a common issue in Ethereum, where a transaction is broadcast but never included in the blockchain due to various reasons such as invalid or incomplete inputs. In this article, we will guide you through the process of analyzing an orphaned transaction using debug.log.

What does debug.log output?

When your machine synchronizes with the Ethereum network, it runs a series of transactions to validate the validity of each block and ensure that all transactions are included in the blockchain. If a transaction is broadcast but not included in the blockchain, you will see errors like ERROR: FetchInputs() : 5b5e32cc97 mempool Tx prev not found or ERROR: FetchInputs() : 5b5e32cc97 stored orphan tx.

Understanding the debug.log output

The debug.log output provides valuable information about the transaction being analyzed. Here’s a breakdown of what each line means:

• ERROR: FetchInputs() : 5b5e32cc97 mempool Tx prev not found e99babf87a:

* FetchInputs() is a function that retrieves the inputs for a given transaction.

* e99babf87a is the hash of the previous transaction in the mempool (Mempool is a queue of pending transactions).

• stored orphan tx 5b5e32cc97 (mapsz 414):

* This line indicates that the transaction being analyzed (5b5e32cc97) was previously broadcast but not included in the blockchain.

* The (mapsz 414) part is a map size, which helps to narrow down the possible locations of the orphaned transaction.

Analyzing an Orphaned Transaction

To analyze an orphaned transaction using debug.log, follow these steps:

• Print the debug.log output: Use a tool like geth-cli or mainnet-ethers.js to print the debug.log output. This will provide you with the error messages and other relevant information.

• Search for orphaned transactions: Look for lines that indicate an orphaned transaction, such as ERROR: FetchInputs() : 5b5e32cc97 mempool Tx prev not found.

• Identify the map size: Check the map size to determine where in the mempool the transaction was broadcast but not included.

• Check previous transactions: Look for other error messages that indicate the previous transaction in the mempool, such as ERROR: FetchInputs() : e99babf87a.

• Use tools like ethers.js or solidity-coverage to analyze the transaction: These tools can help you understand the contract logic and identify potential issues with the transaction.

Example Use Case

Suppose you have a contract that broadcasts a new transaction, but it never includes an orphaned input in the blockchain. You can use debug.log to analyze the transaction and identify where it went wrong:

const debug = require('debug')('ethers:analyze-orphaned-transaction');


// Print debug.log output

console.log(debug.log());


// Search for orphaned transactions

for (let i = 0; i < 10000; i++) {

    const txId = ethers.utils.generateTransaction().hex();

    debug.log(Orphaned transaction found at txId: ${txId});

}


// Identify the map size and previous transactions

const orphans = [];

for (let i = 0; i < 100000; i++) {

    const txId = ethers.utils.generateTransaction().hex();

    if (!debug.log.includes(ERROR: FetchInputs() : ${txId} mempool Tx prev not found)) {

        orphans.push(txId);

    }

}


console.log(orphans);


// Use tools to analyze the transaction

const contract = ethers.contract.fromBytes(buffer);

const tx = contract.methods.myFunction().send();

By analyzing debug.log, you can identify potential issues with orphaned transactions and take steps to fix them. Remember to always use caution when working with Ethereum, and consider using tools like solidity-coverage or ethers.js to help you understand the contract logic.