XPS: FULL: FP: Collaborative Research: Synchrony-aware Primitives for Building Highly Auditable, Highly Scalable, Highly Available Distributed Systems

可审核性是开发高度可伸缩和高度可用的分布式系统的关键属性，因为它能够识别性能瓶颈、事件之间的依赖关系和潜在的并发错误。反过来，对于系统的可审核性而言，时间是一个关键概念。然而，在使用时间方面，分布式系统的理论和实践之间存在着差距。分布式系统理论避开了时间的概念，而考虑了其事件顺序被逻辑时钟捕获的异步系统。实用的分布式系统使用NTP同步时钟来捕获时间，但倾向于使用自组织方法。该项目弥合了这一差距，并提供了支持构建高度可审计、高度可伸缩和高度可用的分布式系统的同步感知系统原语。该项目应用于云计算、分布式NewSQL数据库和全球分布式Web服务。该项目通过组织学术研讨会、向K-12学生外展、招募少数群体以及向社区分发工具和软件来增强对科学/技术的理解，从而产生其他更广泛的影响。为了实现高度可审计的系统，该项目调查了针对延长时间(AT)原语的轻量级和高效设计。AT通过确定如何根据NTP同步的可用性改进和调整逻辑/向量时钟，将因果关系的理论基础和物理时钟的实用性结合在一起。指导AT设计的原则将是“不确定性弹性”。这些AT时钟支持高度可审计的系统，因为它们可以有效地提供全局一致状态快照，而无需等待时钟同步不确定性消失，也无需事先协调。利用这些可审核性原语，该项目构建了对可伸缩和可用系统的支持。为了实现高度可扩展的系统，该项目研究了同步感知协调原语的设计，例如屏障同步、互斥、领导人选举以及因果和完全有序的通信支持。指导同步意识并列原语设计的原则是“沉默同意”。这些原语通过交换从AT时钟收集的计时信息并避免协调所需的显式通信，提高了性能和效率。最后，该项目将利用AT提供的可审核性支持，并将调查检测和纠正分布式系统状态损坏的监视器组件的设计。指导监控器组件设计的原则是“集中监督和覆盖”。

Auditability is a key property for developing highly scalable and highly available distributed systems, as it enables identifying performance bottlenecks, dependencies among events, and latent concurrency bugs. In turn, for the auditability of a system, time is a key concept. However, there is a gap between the theory and the practice of distributed systems in terms of the use of time. The theory of distributed systems shuns the notion of time and considers asynchronous systems whose event ordering is captured by logical clocks. The practical distributed systems employ NTP synchronized clocks to capture time but tend to use ad hoc methods. This project bridges this gap and provides synchrony-aware system primitives that support building highly auditable, highly scalable, and highly available distributed systems. The project has applications to cloud computing, distributed NewSQL databases, and globally distributed web services. The project enables other broader impacts through enhancing scientific/technological understanding via organizing academic workshops, outreaching to K-12 students, recruitment of minority groups, and distributing tools and software to the community.To enable highly auditable systems, the project investigates lightweight and efficient designs for an augmented time (AT) primitive. AT combines the theoretical underpinnings of causality and the practicality of physical clocks by identifying how logical/vector clocks can be improved and tuned based on the availability of NTP synchronization. The principle guiding AT design will be "uncertainty resilience". These AT clocks enable highly auditable systems since they can efficiently provide global consistent-state snapshots without needing to wait out clock synchronization uncertainties and without requiring prior coordination. Leveraging on these auditability primitives, the project builds support for scalable and available systems. To enable highly scalable systems, the project investigates design of synchrony-aware coordination primitives, such as barrier synchronization, mutual exclusion, leader election, and causally and totally ordered communication support. The principle guiding the design of the synchrony-aware coordination primitives is "silent consent". These primitives improve performance and efficiency over their asynchronous system counterparts by trading timing information gathered from AT clocks and avoiding explicit communication needed for coordination. Finally, the project will leverage the auditability support provided by AT and will investigate the design of a monitor component that detects and corrects distributed system state corruptions. The principle guiding the design of the monitor component is "centralized oversight and override".