Recently, I’ve been pondering a question: why is the transaction order on the blockchain so important? It actually involves something called MEV, which stands for Maximum Extractable Value. Simply put, it’s the behavior of block producers (whether miners or validators) earning extra profits by choosing the order of transactions.

It sounds a bit complicated, but the core logic is straightforward. Imagine you are creating a new block, and you have the authority to decide which transactions go in and how they are ordered. If you discover that a certain transaction could trigger an arbitrage opportunity, you can completely adjust the sequence to allow yourself or cooperating searchers to profit from it. That’s how MEV comes into play.

Searchers are an interesting role. They are not block producers, but by analyzing network data, they can identify MEV opportunities. To prioritize their transactions, searchers pay very high fees to block producers. It’s said that in some highly competitive situations, block producers can take up to 99.99% of the potential profit from searchers as fees. For example, in DEX arbitrage, searchers often pay over 90% of the profit to ensure their arbitrage transactions are executed first.

There are three most common forms of MEV. First is arbitrage trading: when the same token’s price differs across different DEXs, searcher bots quickly detect and insert transactions to extract the price difference. Second is front-running: inserting a buy order before a large purchase, raising the price first, then selling afterward—this is called a sandwich attack. The last is forced liquidation transactions: in DeFi lending protocols, when collateral falls below the liquidation threshold, anyone can execute a liquidation and earn a reward; searchers compete to be the first to do so.

Speaking of Ethereum, this topic is especially relevant. Previously, Ethereum used PoW consensus, where miners had the power to reorder transactions, so it was initially called “Miner Extractable Value.” But in September 2022, Ethereum completed the merge, switching to PoS consensus, where validators replaced miners. However, this doesn’t mean MEV disappeared; it actually became more complex. Because validators still have the authority to order transactions, it is now collectively called “Maximal Extractable Value.”

MEV has both advantages and disadvantages. On the positive side, searchers competing to extract arbitrage opportunities lead to rapid price corrections on DEXs, improving market efficiency. The forced liquidation mechanism also helps ensure the stability of lending protocols. But the downsides are clear: ordinary users end up paying higher fees and suffer slippage due to front-running and sandwich attacks. Moreover, when searchers fiercely compete, it drives up the entire network’s gas fees, causing congestion.

The most serious risk is blockchain reorganization. In theory, if the profit from reordering transactions in the previous block exceeds the reward and fees of the next block, block producers are economically incentivized to reorganize the chain to maximize their gains. This poses a threat to the network’s consensus and security.

Currently, the entire industry is seeking solutions to address MEV issues, which has become one of the core topics in blockchain research and development. As the ecosystem evolves, finding a balance between efficiency and fairness will become increasingly critical.