Understanding Ethereum Transactions and Mempool with Alchemy

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Have you ever wondered where your transactions go when you send them to the Ethereum blockchain? What exactly is a pending transaction, and how does it get processed before being mined? In this guide, we'll delve deep into the journey of a transaction on the Ethereum network, from the moment it is sent until it is fully mined. We'll also explore the concept of a mempool and discuss why some transactions succeed while others fail. While this guide focuses on Ethereum, the underlying principles are applicable to most blockchains.

What is an Ethereum Transaction?

At its core, an Ethereum transaction is a user's request to record new information on the blockchain's permanent state. These requests can take various forms, such as a simple value transfer from one account to another, the creation of a new smart contract, or interaction with an existing smart contract.

Understanding the Mempool:

To grasp the transaction flow on Ethereum, it's essential to comprehend the concept of a mempool. The mempool serves as a waiting room within an Ethereum node where unconfirmed transactions reside temporarily. It acts as a staging area and performs crucial steps, including validating transactions and ordering them based on gas prices. Additionally, the mempool shares pending transactions with other nodes, allowing the network to view the list of transactions awaiting confirmation.

The Ethereum Transaction Flow:

Now, let's explore the steps involved in sending a transaction from a user and ensuring its permanent inclusion on the blockchain:

User generates a transaction, signs it with their private key, and sends it to a blockchain node using methods like eth_sendTransaction or eth_sendRawTransaction (e.g., through Alchemy's Supernode API). The transaction enters the mempool of a node. The mempool conducts validation tests, and if successful, the transaction enters a pending state. The node broadcasts the transaction to other nodes in the network, and it enters their respective mempools. When a new block is mined by a node, approximately 200 pending transactions with the highest gas prices are included in the next block. These transactions are removed from the mempool, and the new block and mempool state are propagated across the network. After 5-7 more blocks are confirmed, the chances of blockchain reorganization decrease significantly. At this point, it can be assumed that the transaction is permanently recorded on the blockchain. Possible Issues with Pending Ethereum Transactions:

Full Mempool: The mempool has limits, and if it becomes full, older pending transactions may be dropped to make room for newer ones.

Invalid Parameters: Incorrectly specified parameters in a transaction, such as addresses, values, gas limits, or nonces, can result in errors.

Low Gas Price: Transactions with low gas prices may not be prioritized by miners, potentially leading to delayed or failed confirmations.

Incorrect Nonce: Nonces represent the number of transactions sent from a specific address. If nonces are duplicated or skipped, transactions may not be processed correctly.

Forked Blocks: Occasionally, different sets of nodes may have different views of the blockchain, resulting in parallel chains. In such cases, previously mined transactions on one chain become invalidated when the network adopts another chain.

Using Alchemy Tools for Mempool and Transaction Management:

Alchemy provides tools to simplify the management of mempools and pending transactions. Here are two essential tools:

Alchemy Mempool Watcher: This tool streamlines the complexity of accessing and monitoring the status of transactions in the mempool. It offers real-time information, including transaction statuses, gas prices, durations, and additional details.

Alchemy Explorer: The request/response explorer allows developers to.