Spanner is Google’s scalable, multiversion, globally distributed, and synchronously replicated database. It is the first system to distribute data at global scale and support externally-consistent distributed transactions. This article describes how Spanner is structured, its feature set, the rationale underlying various design decisions, and a novel time API that exposes clock uncertainty. This API and its implementation are critical to supporting external consistency and a variety of powerful features: nonblocking reads in the past, lock-free snapshot transactions, and atomic schema changes, across all of Spanner.

Aspect-oriented programming (AOP) is increasingly gaining in popularity. However, the focus of aspect-oriented language research has been mostly on language design issues; efficient implementation techniques have been less popular. As a result, the performance of certain AOP constructs is still poor. This is in particular true for constructs that rely on dynamic properties of the execution (e.g., the cflow construct).In this paper, we present efficient implementation techniques for cflow that exploit direct access to internal structures of the virtual machine running an application, such as the call stack, as well as the integration of these techniques into the just-in-time compiler code generation process.Our results show that AOP has the potential to make programs that need to define control flow-dependent behavior not only more modular but also more efficient. By making means for control flow-dependent behavior part of the language, AOP opens the possibility of applying sophisticated compiler optimizations that are out of reach for application programmers.