This work addresses the inherent issues of high latency in blockchains and low scalability in traditional consensus protocols. We present pod, a novel notion of consensus whose first priority is to achieve the physically-optimal latency of $2δ$, or one round-trip, i.e., requiring only one network trip (duration $δ$) for writing a transaction and one for reading it. To accomplish this, we first eliminate inter-replica communication. Instead, clients send transactions directly to all replicas, which independently process transactions and append them to local logs. Replicas assigns a timestamp and a sequence number to each transaction in their logs, allowing clients to extract valuable metadata about the transactions and the system state. Later on, clients retrieve these logs and extract transactions (and associated metadata) from them. Necessarily, this construction achieves weaker properties than a total-order broadcast protocol, due to existing lower bounds. Our work models the primitive of pod and defines its security properties. We then show pod-core, a protocol that satisfies properties such as transaction confirmation within $2δ$, censorship resistance against Byzantine replicas, and accountability for safety violations. We show that single-shot auctions can be realized using the pod notion and observe that it is also sufficient for other popular applications.

翻译：本研究针对区块链固有的高延迟问题以及传统共识协议的低可扩展性挑战，提出了一种新型共识概念pod，其首要目标是实现物理最优延迟$2δ$（即一次往返通信），仅需一次网络传输（时长$δ$）完成交易写入，另一次传输完成交易读取。为实现该目标，我们首先消除了副本间的通信机制：客户端直接将交易发送至所有副本节点，各副本独立处理交易并将其追加至本地日志。副本为日志中的每笔交易分配时间戳与序列号，使得客户端能够提取关于交易及系统状态的有价值元数据。随后，客户端通过检索这些日志提取交易及其关联元数据。受现有下界约束，该架构必然弱于全序广播协议的属性强度。本研究对pod原语进行建模并定义其安全属性，继而提出满足以下特性的pod-core协议：在$2δ$时间内确认交易、抵抗拜占庭副本的审查攻击、以及对安全性违规行为的可追责性。我们论证了单次拍卖机制可通过pod概念实现，并发现该框架同样适用于其他主流应用场景。