Mempool
The pool of transactions that have been broadcast to the network but not yet included in a block. There is no single mempool: each node keeps its own, and contents can differ between nodes. Transactions waiting there are publicly visible, which allows automated bots to react to them before confirmation (front-running, sweeping, MEV).
Transactions sent privately to block builders never appear in the public mempool. Transactions that are dropped or replaced before confirmation leave no trace on-chain; evidence of them, and first-seen timestamps, exist only in the records of mempool observers.
Related
Essays
- The Magic of Flash Loans (Part 2): The Next Octave
“Pending transactions waited in a public waiting room, the mempool, where anyone could watch them before they were confirmed.”
- The Magic of Flash Loans (Part 1): Capital Was Never the Constraint
“The barrier does not disappear so much as move, and where it moves to is worth watching: who sees the opportunity first, who can get their transaction into the block on the right terms, who can act without broadcasting their intention into a public mempool, who sits closer to the network, who has built the better machine.”
- Two Sweeps Pointed at the Same Address
“Rescue bundles go out through the relay only, so the funding is never exposed in the public mempool on its own, and nothing can be slipped between the funding and the rescue sweep.”