Public blockchains group submitted transactions into batches, called blocks. A natural question is how to determine which transactions are included in these batches. In this note, we show a gap between the welfare of so-called `fair' ordering, namely first-in-first-out (an ideal that a number of blockchain protocols strive to achieve), where the first transactions to arrive are the ones put into the block, and the welfare of `optimal' inclusion that is, at least approximately, welfare-maximizing, such as choosing which transactions are included in a block via an auction. We show this gap is positive under a simple model with mild assumptions where we assume transactions are, roughly speaking, uniformly drawn from a reasonable distribution. Our results formalize a performance metric for blockchain inclusion rules and consequently provide a framework to help design and compare these rules. The results can be directly extended to ordering mechanisms as well.

翻译：公有区块链将提交的交易分组为批次，即区块。一个自然的问题是，如何确定哪些交易被包含在这些批次中。本注记表明，所谓“公平”排序（即先到先服务——这是许多区块链协议追求的理想状态，即最先到达的交易被放入区块）的福利，与“最优”包含（即至少近似实现福利最大化，例如通过拍卖方式选择哪些交易被包含在区块中）的福利之间存在差距。在一个采用温和假设的简单模型下（我们假定交易大致上服从合理分布），我们证明这一差距为正。我们的结果形式化了区块链包含规则的性能指标，从而为设计和比较这些规则提供了框架。该结果也可直接推广至排序机制。