Mempool Explained: What is a Mempool? Why is it important?

What is Mempool?

The Mempool, a contraction of memory and pool, is a virtual node's storage area for all pending transactions until they are processed and appended to the next block by a miner.

Each node has a different capacity for storing unconfirmed transactions. As a result, each node has its version of pending transactions. A large mempool size shows a lot of network traffic, which means that the average confirmation time will be longer, and the priority fees will be higher.

The Mempool Transaction Count chart shows how many transactions create the congestion; however, the Mempool Size is an excellent statistic for estimating how long the congestion will remain.

Why is Mempool important?

The Mempool is part of BIP-35 (Bitcoin Improvement Proposal No.35), in which outside nodes would be able to access other nodes’ Mempool. This is beneficial in some cases:

Convenience

The mempool's most significant benefit to Bitcoin is its convenience. Users can easily communicate with the network since it is an automatic storage device for pending transactions.

Without a mempool, users would get denied transactions if they did not specify the proper fee. But, as the mempool exists, users can rest assured that, even if the miners' compensation is insufficient, the transaction will remain on the mempool until the volume drops and miners pick it up.

Balancing miner fees

Volume is critical to determine mempool capacity. In turn, it is essential to establish miners’ commissions. If the network is heavily congested and the mempool starts “filling up,” transactions would be stuck unconfirmed for longer times.

Thus, people who need their transactions completed immediately will offer to pay higher fees to the miners. However, as prices start rising, users may be discouraged from operating, waiting for more convenient costs, lowering the volume and driving commissions down again.

Miners will start clearing low-fee transactions when there is less volume. Miners will quickly pick up any new, incoming transaction if the mempool is empty, regardless of the cost. This may encourage users to operate at that specific time, increasing traffic and fee expenses.

A tool such as the mempool provides real-time insights into on-chain metrics. Users can calculate fees for a given transaction, see the network congestion level, and predict the time it will take for their transactions based on the commission they want to pay.

How does Mempool work?

A transaction is broadcast when it is sent from one node to its peers, who subsequently pass it on to their peers. This process repeats itself until the transaction has spread widely enough for miners to include it in a block. Because transactions are not instantly uploaded to the blockchain, this buffer zone is essential.

Nodes will perform a series of tests to ensure that the transaction is genuine, including providing that signatures are correct, outputs do not exceed inputs, and funds have not been spent previously. It will be rejected if it fails to meet these criteria.

Each node has its mempool and unconfirmed transaction storage capacity. A transaction is removed from the mempool when confirmed and included in a block. Nodes share the mempool data by relaying signed transactions from one node to the next until the entire network has received it.

When an overall mempool hits capacity during periods of heavy transaction volume, the node prioritizes transactions based on higher bid transaction fees than the threshold fees.

Any transactions with fees less than the threshold will be removed from the mempool, and only newer transactions with costs that satisfy the minimum will be added back.

This means that higher fee transactions are prioritized to be processed, removed from the mempool, and added to the block.

FAQs about mempool

What happens when the node’s memory is full?

During peak traffic periods, the Bitcoin network might experience a considerable backlog of transactions, lengthening transaction times, and increasing transaction costs. When demand exceeds supply, miners have a lot of flexibility in deciding which transactions to execute first. Even individuals who have paid generous fees may have to wait longer than expected in such situations.

The fact that Bitcoin's blockchain is not easily scalable — which means it's quickly overwhelmed — is one factor contributing to the backlog. You have the choice of waiting it out, switching to the Lightning Network to finish smaller transactions off the main chain, or paying a higher transaction fee when dealing with periods of heavy congestion.

After the transaction has been sent, you have a few options for accelerating it. If your transaction is stuck in the queue, you can use opt-in Replace-by-Charge to jump ahead in line or opt-in RBF to resend your transaction with a higher fee. However, not all wallets enable this feature. If yours doesn't, you'll have to look into other options, such as CPFP (child pays for parent).

Miners use CPFP to select transactions with the highest combined fees. You can also employ a transaction accelerator, which allows you to submit transactions to the ViaBTC mining pool for priority confirmation if they are at least 0.1 mBTC per kilobyte.

Finally, the Lightning Network, a Layer 2 solution, can be used. The Lightning Network allows you to create a new channel, complete as many off-chain transactions from the traditional Bitcoin network as you want, and terminate the payment channel once the transactions are verified. You can virtually avoid the clogged queue using the Lightning Network, and your expenses may be greatly reduced.

If neither the Lightning Network nor any other solution is available, rest assured that your bitcoin will not be lost. It'll stay in your wallet until the transaction is completed.

Why should we know about Mempool?

Exchange front-running bots can monitor large pending transactions on the mempool and utilize them for profit.

Before being added to new blocks on the blockchain, every transaction in Bitcoin and similar blockchains must pass through the Mempool. Mempool captures and holds transactions during periods of high traffic and congestion until Miner Nodes can add them to new blocks.

Mempool, on the other hand, has a significant impact on Miner Extractable Value (MEV). Miner Nodes are not required to process transactions in which users place orders on the blockchain, but they might prioritize transactions that pay greater fees or orders that benefit them. MEV has two major drawbacks:

• Arbitrage trading bots of third parties.
• Exchange front-running bots can keep track of huge pending transactions on the mempool and profit from them.