Mempool

Written by Alex Gedevani

Introduction

In the Bitcoin protocol, the mempool is the pool of pending unconfirmed transactions waiting to be added to the blockchain by miners. The name of the pool can vary on different networks.

The mempool is like a “waiting area” where thenode holds the pending transactions. There are a variety of mempool sizes and transaction counts as nodes have different capacities for storing these unconfirmed transactions. After being picked up from the pool by a Bitcoin miner, the transaction is then inserted into the next block. Once inserted into a successfully mined block, the transaction is confirmed.

During the 2017 bull market, the network was frequently clogged with instances of upwards of 220,000 transactions in the mempool for hours despite higher fees. This occurs when new transactions arrive at a higher rate than they are being cleared from the mempool into mined blocks.

When the mempool reaches full capacity, nodes begin prioritizing transactions by setting up a minimal fee threshold. Senders of the transactions signal how urgently they’d like the transaction to be confirmed by adjusting the fee they are willing to pay. The higher the fee the faster the transaction will get confirmed and vice versa.

Suggested Reading

An in-depth guide into how the mempool works by Marion Deneuville

Bitcoin Mempool: Everything You Need To Know About It by Sudhir Khatwani

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