What is Mempool Bitcoin


What is Mempool

If you are interested in cryptocurrencies, you have probably heard the term “mempool” or the memory pool more than once, and most likely you didn’t pay much attention to it, because at first glance it does not play any role for you. But in fact it is quite important and today we will tell you what it is and why you need it.

In simple terms, the mempool is a “waiting area” for blockchain transactions, which each full node supports for itself. After the transaction has been verified by the node, it waits inside the memory pool until it is taken by the miner for placement in the block. Any operation that occurs within the network first requires verification by all available nodes (that is, the computers involved in the work).

After the operation passes the verification successfully, it falls into the zone of verified but not yet confirmed transactions. There it is stored until it is included in the blockchain. Each has its own waiting area and everyone has a different volume.

Periodically, the number of transactions in the node memory exceeds the permissible norms and an overload occurs. In this case, the priority of transactions is applied – this is affected by the size of the commission that the user sets for his operation. Holders of digital currencies periodically encounter a situation where their transactions are returned back without processing. This is due to pool memory congestion and low commission.

Priority is given to operations with the highest possible commission: they are first added to the block, and all transactions that do not reach the lower threshold of the commission are simply deleted.

 Why is it important

Mempool is part of BIP 35 (Bitcoin Improvement Proposals), that is, one of the improvements developed for the Bitcoin blockchain. The idea was that external nodes would be able to access Mempool from other nodes.

This is useful for:

  • SPV customers (also known as lightweight wallets or wallets with simplified payment verification) who want to know about transactions before they are approved and entered into the block.
  • Miners who want to check the profitability of fees or download the current “transaction pending list” to start confirmation.
  • For those wishing to conduct remote network diagnostics in order to understand the speed of processing payments and transfers. For example, if Mempool is about 3 MB in size, most transactions will have to wait at least one or two blocks until they are confirmed. This is due to the fact that each block is 1 MB in size, so up to 3 confirmations may be required to clear the entire mempool (assuming that no new transactions arrive). Keep in mind that some of Mempool’s transactions are low priority transactions, and their sender knows that it will take a long time to confirm them, such as “junk transactions” (sending small amounts).


How long does it take to confirm a bitcoin transaction?

On average, a new Bitcoin transaction block is mined every 10 minutes. This is an average value, that is, in fact, it can take 1 minute or 1 hour. Each block contains several thousand transactions. Depending on the transaction fee, you can estimate how long it will take to confirm (again, approximately).

What should I do if my transaction is stuck in Mempool?

As a rule, if you wait long enough (usually about 48 hours), your transaction will be thrown out of the memory pool and the funds will be returned to your wallet. However, to speed up transaction confirmation, you can do the following:

  • Use replacement (RBF) – some wallets (for example, Electrum) allow you to replace an existing transaction with a new one with a higher commission.
  • Apply transaction accelerators – some mining pools provide the service of accelerating certain transactions for a fee or in a queue.


Mempool is a very important part of the Bitcoin network. This allows us to understand how busy the network is and whether there are “transaction jams” that lead to slower confirmation times and higher rates. We hope that this term will no longer cause you questions.

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