What is Mempool?

A mempool is where an unconfirmed transaction waits after being verified by a node and before being included in a block. The mempool makes use of the Replace by Fee (RBF) mechanism, which allows transactions with higher transaction fees to supersede earlier transactions with lower fees paid. When many transactions are pending in the mempool, network traffic becomes more congested and the average confirmation time increases. Network nodes must check to ensure that transactions within the mempool are valid by verifying correct signature schemes, that outputs do not exceed inputs, and that funds have not been double spent.