If you’ve ever bought an NFT, exchanged cryptocurrency, or simply transmitted funds from your wallet to another address, you may have encountered transaction delays. But have you ever thought about where your transaction is throughout that time?

It can be stressful to see your cash in a pending position. “Did it work?” or “Has my transaction failed?” you may be wondering. While the transaction is still pending, it is routed to a special location known as a crypto mempool to await approval. But what exactly is a mempool, and how does it work?

To put it simply, “mempool” is a contraction of the phrases “memory” and “pool”. However, the mempool’s role in blockchain technology is a little more complicated than that.

So let’s dive in.

What Is a Mempool?

A mempool is a blockchain node’s version of a queue for unapproved transactions. When you start it, it automatically joins the queue in the mempool before being processed on the blockchain.

What Is The Purpose Of A Mempool?

Mempools are an essential component of how a blockchain node works. To put it another way, approving a blockchain transaction entails adding it to a new block on the blockchain. However, not all network participants can construct new blocks. Only crypto miners, for example, can build blocks on proof-of-work blockchains like Bitcoin. Only validators can build blocks on proof-of-stake blockchains like Ethereum.

As a result, when you sign a transaction, you must rely on a miner or a validator to include it in a block and broadcast it to the network. However, there could be a delay between you approving the transaction and it being broadcast to the network. Meanwhile, the transaction requires a location to wait, and it does so in a place called the mempool.

How Does A Mempool Work?

It is important to notice that each chain does not have a single mempool. In fact, each node on each chain has a mempool that receives different transactions at different times. So, how exactly does that work?

Transactions in a mempool can be in one of two states: queued or pending. When the nodes validate the queued transactions, they become pending transactions. Miners can only add pending transactions to a block at that point.

Mempool Work

Assume you want to send 1 ETH to a friend. You enter your friend’s wallet address, enter the gas fee, and then press the “Send” button. At this point, your transaction is “queued” and enters your mempool. It is then disseminated over the network of nodes. However, it is not added to the blockchain just yet.

Instead, each node verifies that the queued transaction is genuine. If the nodes do not discover an issue, the transaction is moved from the “queued” to the “pending” status. A miner or validator will eventually pick up the pending transaction from their node’s mempool and add it to a new block. Following that, your transaction is approved, and your friend receives 1ETH. The remaining nodes then interact with one another to remove the transaction from their mempools.

Why Is My Transaction Still In The Mempool?

There are several possible causes for your transaction to be stalled. So let us investigate what they could be.

Network Congestion

The most common cause of transactions becoming stuck in the mempool is network congestion.

Remember how miners and validators will finally add a legitimate transaction to a block? Thousands of transactions are submitted at any given time. So, how do they decide which transaction to complete first?

Simply said, miners and validators prioritize transactions with the highest payouts.  As a result, when the network is congested, transaction prices rise because some participants are ready to pay higher transaction fees in order for their transaction to be completed first. That is, if you submit a transaction during a busy period, you must match the price at which others on the network are willing to pay.

In essence, it’s comparable to how taxi prices work in several nations. If it’s a busy Friday night, your cab may be pricey and take a long time to arrive. On a calm afternoon, the same trip will cost half as much and take twice as long. On the blockchain, that taxi driver is your miner or validator, and they have the authority to accept the transactions for which they want the rewards.

While this may appear to be selfish on the part of the blockmakers, the system is designed in this manner. When the system is overburdened, it will prioritize transactions that give the highest rewards. This means that transactions with insufficient fees may be dropped, but this is not the end of the story. Even a transaction that is moved out of the mempool may be picked up by a node and replayed later.

You Set The Gas Fee Too Low

Another reason your transaction may be delayed in the mempool is that you set the gas charge too low, making it impossible for a miner or validator to pick it up. If you make a really low offer, the network will never be quiet enough to execute your transaction. To discover more, read the whole article on cryptocurrency gas fees.

Transaction Priority

In the mempool, transactions are sorted by various factors, including transaction fees. Miners, who validate and add transactions to the blockchain, typically prioritize transactions with higher fees. This creates an incentive for users to offer higher fees if they want their transactions to be processed quickly.

The Hash Rate Drops

Transactions on the Bitcoin network might become blocked if the hash rate falls. Simply said, in these cases, the network lacks the physical computer capability to process the volume of pending transactions.

Now that you know why, let’s look at some of the possible answers.

How Do I Release My Transaction From The Mempool?

It can be challenging to release your transaction from the mempool. It’s not a one-size-fits-all operation, and you have a few options. Your choice will be based on the circumstances surrounding your transaction’s initial snag in the mempool.

There are three primary alternatives available, but it’s crucial to remember that each blockchain will use a different set of identical procedures.

  • Transaction Speed: The time a transaction spends in the mempool can vary. Transactions with higher fees are usually processed faster, as miners are more inclined to include them in their blocks.
  • Transaction Fees: Transaction fees are essential for prioritizing transactions in the mempool. Users who offer higher fees have a better chance of having their transactions processed promptly.
  • Network Congestion: During times of network congestion, the mempool can become crowded with unconfirmed transactions, leading to delays in processing and higher fees.
  • Double-Spending Prevention: The mempool plays a crucial role in preventing double-spending. Transactions that spend the same cryptocurrency twice are rejected, ensuring the integrity of the blockchain.
  • Temporary Storage: The mempool is a temporary storage area. If a transaction is not included in a block promptly, it may be dropped from the mempool after a certain period, returning the funds to the sender.


In the world of cryptocurrencies, the mempool is a critical component of transaction processing. It acts as a temporary holding area for transactions, determining which ones are prioritized based on fees. While it might seem like a complex concept, understanding the mempool is essential for cryptocurrency users, as it explains why transactions may take longer during network congestion and why transaction fees can vary. In essence, the mempool is a crucial cog in the machinery that keeps blockchain networks running efficiently and securely.


Q. What is the purpose of the Mempool?
A. The mempool (short for “memory pool”) is a critical component in blockchain networks like Bitcoin. Its purpose is to temporarily store pending transactions that have been broadcast to the network but haven’t yet been included in a block. Miners or validators select transactions from the mempool to include in the next block they create. This queue ensures a smooth transaction flow, allowing for consensus and order in a decentralized network.

Q. What is the Mempool in blockchain?
A. The mempool, short for “memory pool,” is a temporary storage area in a blockchain network where pending transactions are held before they are added to a block and confirmed on the blockchain. Miners or validators select transactions from the mempool and include them in the next block. This process ensures the order and security of transactions on the blockchain.

Q. What is the Mempool for Ethereum?
A. The Ethereum mempool, short for “memory pool,” is a temporary storage area for pending transactions on the Ethereum blockchain. It holds transactions that are waiting to be confirmed and added to the blockchain. Miners select transactions from the mempool to include in the next block, typically prioritizing those with higher gas fees. This system helps ensure the efficient processing of transactions on the Ethereum network.

Q. How long does a transaction stay in Mempool?
A. The length of time a transaction remains in the mempool (memory pool) of a blockchain network can vary significantly. It depends on factors like network congestion, transaction fees, and the specific blockchain protocol. In most cases, transactions are removed from the mempool after a certain period, typically a few days. However, if the network is congested or the transaction fee is too low, it might take longer or even be dropped without confirmation.

Q. What is the maximum size of Mempool?
A. The maximum size of a mempool, short for “memory pool,” can vary depending on the specific blockchain or network it is associated with. Mempool sizes are not fixed and can fluctuate based on factors like network congestion and transaction volume. For example, the Bitcoin mempool typically has a capacity of around 300MB, but it can temporarily exceed this limit during periods of high activity. The maximum size of a mempool is determined by network parameters and can change over time as the network’s capacity is adjusted or as software updates are implemented.