Understanding the Mempool: Your Guide to Unconfirmed Transactions

The mempool, short for "memory pool," is a critical component of blockchain technology, particularly in cryptocurrencies like Bitcoin. It\'s a dynamic holding area for all valid, unconfirmed transactions waiting to be included in a block and added to the blockchain. Think of it as a waiting room for transactions hoping to be mined.

How the Mempool Works

The mempool is not a central or shared pool; every node has its own separate mempool. This means each node maintains its own list of pending transactions. When you initiate a transaction, it\'s broadcast to the network, and nodes independently verify and, if valid, store it in their mempool. Miners then select transactions from their mempool to include in the next block.

Key Aspects of the Mempool

Transaction Broadcasting: After initiating a transaction, it\'s broadcast to the network. If the message is accurate, it means that the sender submitted the transaction to the network and it is in queue to be included in the blockchain.

Location of Broadcasted Transactions: Where is a broadcasted TX located at before it\'s nLocktime reached? In mempool or not? The answer is, generally, in the mempool.

Fees and Prioritization: Miners prioritize transactions with higher fees. This means transactions with higher fees are more likely to be included in the next block. You clearly can see that the mempool is cyclical and you can set a very low fee if you are not in a hurry. This is also an overview of the current mempool status.

Mempool Size Limit: Note that the mempool size limit does not pertain to the serialized data or the transaction weight of the queued transactions (which is what is written to the block and what...). So, what if the mempool exceeds 300 MB? Nodes have rules to evict transactions, usually based on fee rate and age. Older, low-fee transactions are often removed.

Transaction Expiration: Secondly, transactions residing in the mempool for over two weeks expired. By default, Bitcoin Core nodes remove transactions from their mempool if no miner found.

Node Rebroadcasting: Does my node rebroadcast its mempool transactions on startup? Why rebroadcasting transactions in the Bitcoin Core? The answer depends on the node\'s configuration. While some nodes rebroadcast, this behavior can be configured.

Monitoring the Mempool

For real-time monitoring of the mempool and transaction status, I think you should use websocket or Webhook connection to a mempool node. Then you can set up filters on the node to only receive PancakeSwap V3 txs for example, and avoid unnecessary data.

If you\'re using Electrum as your wallet and see an attribute with the name "Position in mempool" and the value is 8.61 MB from tip, it means that transaction is that far down in the mempool.

Understanding Common Misconceptions

Historical Data: TL;DR: They include debits and credits from historical transactions in the blockchain, not just unconfirmed mempool transactions. The Total Received includes not...