All bitcoin transactions throughout history need to be recorded and secured on its blockchain-based ledger. As some call it, the blockchain or time chain is a database that records all transactions. Since millions of people use the chain daily, you can imagine how chaotic organizational transactions can become, and there needs to be some order method.
This is where the mempool comes in; the mempool (memory pool) is a smaller database filled with unconfirmed or pending transactions, which every node keeps track of on the bitcoin network. When a user signs a transaction using a set of private keys and broadcasts the transaction to the network of nodes, it’s added to the mempool.
Transactions made up of UTXOs wait to be picked up by miners and added to the next block. When a transaction is confirmed by being included in a block, it is removed from the mempool.
Nodes share mempool data by relaying signed transactions to each other, but there is no single mempool, and few nodes keep the entire mempool.
Miners draw transactions from the mempool to include in their blocks and typically select transactions based on who provides the highest mining fees. Transactions can live in the mempool for some time before being picked up. With tools like “check template verify, “transactions can live in the mempool until specific predetermined criteria are met.