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Definition: What is a mempool?

A mempool (short for memory pool) is a data structure used by cryptocurrencies to temporarily store pending transactions that have been broadcast to the network and have not yet been included in a block (for confirmation).

When a user sends a transaction, it is broadcast to the blockchain network and initially stored in the mempool of each node that receives it. Additionally, before adding a transaction to its’ mempool, a node will validate that the transaction complies with the network’s rules.

The mempool is not a master reference shared universally by all nodes. There’s no “one” mempool. This means each node configures its own rules for the node’s mempool. In fact, a node can be the first to receive a transaction but it is possible that it might not have propagated the transaction to the rest of the network.

Explanation: What are mempools used for?

Memory pools are common in blockchain protocol implementations and used to store pending transactions while other operations are done to include the transactions in their block proposal to the network.

Transactions that are not included in a block remain in the mempool and depending on the network implementation they may be dropped due to network congestion or due to expiration of their validity period.

The mempool is an important component of blockchain networks like Bitcoin and Ethereum because it serves as a temporary holding area for unconfirmed transactions.

Applications of mempools

  • Transaction validation
  • Transaction prioritization
  • Block creation
  • Network congestion analysis
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