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Definition: mempool


(MEMory POOL) An area in memory (RAM) in blockchain validator nodes dedicated to holding incoming crypto transactions that have been broadcast to the network from exchanges, wallets and decentralized apps (dApps). Also called a "transaction pool" and "preconsensus layer." The size of the mempool determines the maximum number of transactions held.

The node accepts new transactions into its mempool and determines if they have a valid format and suitable fee. Account balances are also checked if funds are being transferred. If the node considers the transaction valid, it is broadcast to other nodes. There may be dozens, hundreds or even thousands of mempools active for a blockchain, and mempools contain a unique mix of transactions at any moment. All transactions do not reach every node.

The Go-to Place for Transactions
Miners grab transactions from their local mempools typically prioritizing transactions with the highest fees first. After a miner has been designated to add the next new block, either by solving a puzzle or being randomly chosen, the new block is broadcast to all validator nodes. Nodes eliminate transactions in their mempools that are in the new block or have conflicts with it. See crypto mining and Blocknative.