Glossary · Ledger

Mempool.

A node-local pool of pending transactions waiting to be included in a block.

Think of it as

The queue at the airport gate. Transactions sit there until the next slot leader (block producer) calls them up.

In depth

Submitted transactions sit in the mempool until a block producer picks them up. On fee-market chains (Bitcoin, Litecoin, etc.) higher fees move a transaction up the queue. On Cardano the minimum fee is deterministic (min_fee = a·size + b), with Plutus transactions paying additional execution-unit costs for declared memory and CPU steps; either way there is no bidding and no fee market. On eUTxO chains, transactions only conflict if they spend the same UTxO, so independent transactions can be included in parallel without ordering constraints.

Example

During a busy moment your transaction may sit in the mempool for a few slots before the next elected block producer picks it up.

Try it interactively Watch transactions flow into blocks

Next on this path

  1. Transaction fee The ada paid to the network for including a transaction. Deterministic on Cardano.
  2. Fee market A pricing regime where users bid for inclusion. Higher fees mean faster confirmation.
  3. Block An ordered batch of transactions appended to the chain by the slot leader.