How Does a Node Decide Which Low-Fee Transactions to Drop from Its Mempool?

Nodes have a finite amount of memory to store unconfirmed transactions. When the Mempool becomes full, nodes must prune or drop transactions to make space for new, higher-fee ones.

The decision is typically based on the transaction's fee-per-byte (or fee-per-gas). Transactions below a certain minimum fee threshold or those that have been pending for an excessive duration are usually the first to be dropped.