Ethereum Mempool: Everything to Know

By  Beluga Research August 6, 2023

Image for Ethereum Mempool: Everything to Know


  • The Ethereum mempool is a temporary storage area where pending transactions are held before being confirmed and added to the blockchain
  • Understanding the basics of the Ethereum network and the role of miners in validating transactions is crucial for comprehending the concept of the mempool
  • Key aspects of the Ethereum mempool include transaction propagation through the network, the use of gas prices to prioritize transactions and dynamic transaction prioritization
  • The Ethereum mempool include is decentralized nature, with the use of gas to quantify computational effort and transaction prioritization


The Ethereum mempool is a temporary storage area where pending transactions are held before being confirmed and added to the blockchain. It is short for "memory pool" where incoming transactions are held before they are processed and added to the blockchain. It serves as a waiting area where transactions wait to be validated by miners and incorporated into a block.

The mempool acts as a buffer between users initiating transactions and the actual confirmation of those transactions on the Ethereum network. It ensures that transactions are not lost or discarded while awaiting confirmation.

A Brief History

To understand the importance of the Ethereum mempool, it is essential to have historical context. The concept of mempools originated with the Bitcoin network, the first and most well-known cryptocurrency. Bitcoin's mempool was introduced as a means to handle the increasing number of transactions and prevent issues such as double-spending. Ethereum, being a blockchain platform with smart contract capabilities, also adopted the mempool concept to manage the influx of transactions and maintain the integrity of its network.

Ethereum Mempool: Everything to Know

  • Transaction Propagation: When a user initiates a transaction on the Ethereum network, it propagates through the network nodes until it reaches the mempool. Nodes are responsible for relaying transactions to other nodes, ensuring widespread dissemination. This propagation process allows the transaction to be visible to miners who will ultimately include it in a block.
  • Gas Price: Ethereum introduces the concept of gas, a unit that measures computational effort required to execute a transaction or a smart contract. Users attach a gas price to transactions, indicating the amount they are willing to pay for miners to process their transaction. The gas price plays a crucial role in determining the priority of a transaction within the mempool. Higher gas prices incentivize miners to prioritize the transaction, leading to faster confirmation.
  • Transaction Prioritization: The Ethereum mempool employs a transaction prioritization mechanism based on the gas price and the order of arrival. Transactions with higher gas prices are given higher priority and are more likely to be included in the next block. This incentivizes users to offer competitive gas prices if they want their transactions to be processed promptly. However, it is worth noting that even transactions with lower gas prices have a chance of being included in subsequent blocks.
  • Mempool Size: The size of the Ethereum mempool fluctuates based on network activity. During periods of high transaction volume, the mempool can become congested, resulting in delays and higher gas prices. Miners prioritize transactions with higher gas prices, leaving lower-priced transactions in the mempool until network congestion subsides. As the mempool has a finite capacity, transactions with very low gas prices may eventually be dropped if they remain unconfirmed for an extended period.
  • Transaction Removal: Transactions that remain unconfirmed for an extended period may be removed from the mempool. This removal process helps prevent the mempool from becoming bloated with stale or low-value transactions. Ethereum nodes typically have configurable policies that dictate the duration for which transactions can remain in the mempool before being removed.

Getting Started

To grasp the concept of the Ethereum mempool, it is important to first understand the basic structure of the Ethereum network. Ethereum is a decentralized blockchain platform that enables the execution of smart contracts and the development of decentralized applications (Dapps). Transactions on the Ethereum network involve the exchange of ether (ETH), the native cryptocurrency of the platform.

When a user initiates a transaction on Ethereum, such as sending ETH or interacting with a smart contract, the transaction is broadcasted to the network. Before a transaction can be included in a block and added to the blockchain, it needs to be validated by the network's participants, known as miners or validators. The process of validating transactions involves solving complex mathematical puzzles, known as mining or validation.

Unique Aspects

The Ethereum mempool exhibits several unique aspects that distinguish it from traditional centralized payment systems. One of the key features of the Ethereum mempool is its decentralized nature. Unlike traditional financial systems where a central authority oversees transaction processing, the Ethereum mempool relies on a distributed network of miners and validators to validate and process transactions.

Another important aspect of the Ethereum mempool is the concept of gas. Gas is a unit of measurement that quantifies the computational effort required to execute a transaction or perform an operation on the Ethereum network. Each transaction specifies a gas limit and a gas price. The gas limit represents the maximum amount of computational work the transaction is allowed to consume, while the gas price indicates the fee paid to miners for each unit of gas consumed.

The Ethereum mempool also employs a mechanism called transaction prioritization. Transactions with higher gas prices are typically given priority for inclusion in the next block. This incentivizes users to set higher gas prices to ensure transactions are processed quickly. However, it's important to note that setting an excessively high gas price may result in unnecessary fees.

Furthermore, the Ethereum mempool implements a mechanism known as transaction nonce. The nonce is a sequential number associated with each transaction from a specific sender. It ensures that transactions from the same sender are executed in the intended order and helps prevent double-spending. Miners validate transactions based on their nonce, ensuring that they are executed in the correct sequence.


  • Efficient Transaction Processing - The mempool allows for efficient transaction processing by acting as a temporary storage area for pending transactions. Miners pick transactions from the mempool to include in the next block they mine, ensuring that transactions are processed in a timely manner.
  • Flexibility in Transaction Fees - Ethereum's mempool enables users to set thier desired transaction fees. This flexibility allows users to prioritize transactions based on urgency and cost considerations. Users can choose to pay higher fees for faster confirmation or opt for lower fees if they are not time-sensitive.
  • Decentralization - The mempool contributes to the decentralized nature of Ethereum by ensuring that transactions are processed by a diverse set of miners. Miners select transactions based on their own preferences, which helps prevent centralization and ensures a fair and open transaction processing system.
  • Transparency - The mempool provides transparency by allowing users to monitor the status of transactions. Users can observe their transaction's position in the mempool and track its progress towards confirmation. This transparency helps build trust and confidence in the Ethereum network.
  • Preventing Double Spending - The mempool plays a vital role in preventing double spending, a malicious act where a user attempts to spend the same cryptocurrency more than once. By temporarily storing pending transactions, the mempool ensures that each transaction is processed only once, maintaining the integrity of the Ethereum network.


  • Transaction Delays - During periods of high network congestion, the mempool can become crowded with pending transactions. This congestion can lead to delays in transaction confirmations as miners prioritize transactions with higher fees. Users who set lower fees may experience longer waiting times for their transactions to be included in a block.
  • Price Volatility - The cost of transaction fees on the Ethereum network is influenced by various factors, including network demand and congestion levels. This volatility in transaction fees can make it challenging for users to predict and plan transaction costs accurately.
  • Potential for Front-Running - Front-running refers to the practice of a miner or a malicious actor prioritizing their own transactions or manipulating the order of transactions in their favor. While the mempool itself does not directly facilitate front-running, the dynamics of transaction selection from the mempool can create opportunities for such practices.
  • Scalability Challenges - As the Ethereum network continues to grow in popularity, scalability challenges may arise. The mempool's efficiency may be affected during periods of high network activity, leading to increased transaction fees and longer confirmation times.
  • Resource Requirements - Running a full node and maintaining a mempool can require significant computational resources and storage capacity. This can pose challenges for individuals or entities with limited resources or those operating in resource-constrained environments.