All nodes maintain a transaction pool to store pending transactions before processing.
Options and methods for configuring and monitoring the transaction pool include:
txpool_besuTransactionsJSON-RPC API method to list transactions in the transaction pool.
--tx-pool-max-sizecommand line option to specify the maximum number of transactions in the transaction pool.
--tx-pool-retention-hourscommand line option to specify the maximum number of hours to keep pending transactions in the transaction pool.
droppedPendingTransactionsRPC subscriptions to notify of transactions added to and dropped from the transaction pool.
Dropping transactions when the transaction pool is full
When the transaction pool is full, it accepts and retains local transactions in preference to remote transactions. If the transaction pool is full of local transactions, Besu drops the oldest local transactions first. That is, a full transaction pool continues to accept new local transactions by first dropping remote transactions and then by dropping the oldest local transactions.
Replacing transactions with the same sender and nonce
For transactions received with the same sender and nonce as a pending transaction but a higher gas price, Besu replaces the pending transaction with the new one with the higher gas price.
Size of the transaction pool
Decreasing the maximum size of the transaction pool reduces memory use. If the network is busy and there is a backlog of transactions, increasing the size of the transaction pool reduces the risk of removing transactions from the transaction pool.