Modern blockchains increasingly rely on parallel execution to improve throughput. We show several industry and academic transaction fee mechanisms (TFMs) struggle to simultaneously account for execution parallelism while remaining performant and fair. First, if parallelism affects fees, adversarial protocol manipulations that offset possible benefits to throughput by introducing fake transactions become rational: users can insert functionally useless parallel transactions solely to reduce fees, and schedulers can create useless sequential transactions to increase revenue. Execution contingency, a core feature of expressive programming languages, both exacerbates the aforementioned threats and introduces new ones: (1) users may overpay for unused resources, and (2) scheduler revenue is harmed when reserved scheduling slots go unused due to contingency. We introduce a framework for this challenging setting, and prove an impossibility, highlighting an inherent tension: both parallelism and contingency involve a trade-off between minimizing risks for users and schedulers, as favoring one comes at the expense of the other. To complete the picture, we introduce a fee mechanisms and prove that they achieve the boundaries of this trade-off. Our results provide rigorous foundations for evaluating designs advanced by notable blockchains, such as Sui and Monad.

翻译：现代区块链日益依赖并行执行以提高吞吐量。我们证明，若干业界与学术界的交易费用机制（TFM）在兼顾执行并行性、维持高效性与公平性方面存在困难。首先，若并行性影响费用，攻击者可通过引入虚假交易抵消吞吐量潜在收益的协议操纵行为将变得理性：用户可插入功能上无用的并行交易仅以降低费用，调度者则可创建无用的串行交易以增加收入。执行偶然性——表达性编程语言的核心特性——既加剧了前述威胁，又引入了新的问题：（1）用户可能为未使用的资源超额支付；（2）当预留的调度槽因偶然性闲置时，调度者收入将受损。我们针对这一具有挑战性的场景构建了框架，并证明了一个不可能性结论，突显了固有的矛盾：并行性与偶然性均涉及用户与调度者风险最小化之间的权衡，偏向一方必然以牺牲另一方为代价。为完善图景，我们引入费用机制并证明其实现了该权衡的边界。我们的结果为评估Sui与Monad等知名区块链所提出的设计方案提供了严谨基础。