Mempool

What Is the Mempool?

The mempool is a buffer maintained by each blockchain node that stores pending transactions waiting to be included in the next block. When you submit a transaction — such as a DEX swap or token transfer — it is broadcast to the network and enters the mempools of connected nodes. The transaction remains there until a validator or miner selects it for block inclusion.

Each node maintains its own version of the mempool, so the exact contents can vary between nodes depending on network propagation. Transactions with higher gas fees are typically prioritized for inclusion.

How the Mempool Affects Trading

The public nature of the Ethereum mempool creates a significant challenge for DeFi traders. MEV bots constantly scan the mempool for profitable opportunities, including pending DEX swaps that can be front-run or sandwiched. A trader submitting a $10,000 Uniswap buy into the public mempool is essentially broadcasting their intent to every MEV bot on the network.

This visibility is why private transaction submission services (like Flashbots Protect and MEV Blocker) have become popular. These services route transactions directly to block builders without broadcasting them to the public mempool, hiding them from MEV searchers.

Mempool Differences by Chain

Not all blockchains have public mempools in the same way. Solana does not have a traditional mempool because transactions are forwarded directly to the current block producer via a leader schedule. This architectural difference means MEV on Solana operates differently, though Jito's block engine provides a similar mechanism for searchers to bid on transaction ordering.