🥩 frontrunning (or PGA, priority gas auction)
tl, dr
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determine what gas price is required to win a gas auction.
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process by which an adversary observes transactions on the network layer and then acts upon this information by, for instance, issuing a competing transaction, with the hope that this transaction is mined before a victim transaction.
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example: transaction A is broadcasted with a higher gas price than an already pending transaction B so that A gets mined before B.
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rather than programming complx algorithms to detect profitable MEV opportunities, some searchers run generalized frontrunners. These are bots that watch the mempool to detect profitable transactions.
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frontrunners will copy the potentially profitable transaction's code and replace addresses with theirs. Then, they submit the modified transaction with the replaced address and a higher gas price, frontrunning the original transaction and getting the searcher's MEV.