Mempool

When a transaction is broadcast, nodes hold it in their memory pool (mempool) until a block producer picks it up. Producers generally choose the transactions that pay the most per unit of block space, so when demand rises, low-fee transactions wait, sometimes for hours.

Two practical consequences:

• A broadcast transaction isn't settled. It can sit unconfirmed, be replaced, or be dropped if it waits too long.
• Fees are an auction. The fee that was enough a minute ago may not be now.

Different networks behave differently. Bitcoin's mempool is the classic case, where replace-by-fee lets a sender raise the fee of a waiting transaction. On Ethereum-style networks a waiting transaction also blocks the sender's later ones, because of the nonce.

On Valtu

Payouts move to BROADCAST once sent and to CONFIRMED only when final. If a payout is slow, fees are bumped automatically. On Bitcoin, a payout still unconfirmed 30 minutes after broadcast is replaced with a higher-fee version that spends the same coins to the same recipient.