A mempool (an abbreviation of memory and pool) is a node’s mechanism for keeping track of storing information on unconfirmed transactions. The mempool works like a waiting room for every transaction that hasn’t entered a block yet.
To submit a transaction to miners, nodes must depend on other nodes until it has propagated across the network. This is where the role of the mempool as the node’s holding area for all pending transactions.
Mempool has the same number of nodes. However, each mempool can have a different size. This is because each node does not receive the same transaction at the same time. So, some nodes will store more information. The size of the mempool has quite an impact on the transaction processing speed. The reason is when the transaction volume is very high and makes the mempool size bigger; it will prioritize transactions with the highest transaction fees. This situation can lead to many MEV opportunities (which can negatively impact users).
In this case, the user can pay a higher fee to prioritize his transaction. If not, users can wait until the transaction volume decreases, then the transaction will be processed. Each confirmed transaction will be removed from the mempool, thereby reducing the size of the mempool.
Learn more about blockchain and how it works in the following article.