Declarative Systems

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Abstract Declarative Systems Building system software is a notoriously complex and arduous endeavor. Developing tools and methodologies for practical system software engineering has long been an active area of research. This thesis explores system software development through the lens of a declarative, data-centric programming language that can succinctly express high-level system specifications and be directly compiled to executable code. By unifying specification and implementation, our approach avoids the common problem of implementations diverging from specifications over time. In addition, we show that using a declarative language often results in drastic reductions in code size (100× and more) relative to procedural languages like Java and C++. We demonstrate these advantages by implementing a host of functionalities at various levels of the system hierarchy, including network protocols, query optimizers, and scheduling policies. In addition to providing a compact and optimized implementation, we demonstrate that our declarative implementations often map very naturally to traditional specifications: in many cases they are line-by-line translations of published pseudocode. We started this work with the hypothesis that declarative languages — originally developed for the purposes of data management and querying — could be fruitfully adapted to the specification and implementation of core system infrastructure. A similar argument had been made for networking protocols a few years earlier [61]. However, our goals were quite different: we wanted to explore a broader range of algorithms and functionalities (dynamic programming, scheduling, program rewriting, and system auditing) that were part of complex, real-world software systems. We identified two existing system components — query optimizers in a DBMS and task schedulers in a cloud computing system — that we felt would be better specified via a declarative language. Given our interest in delivering real-world software, a key challenge was identifying the right system boundary that would permit meaningful declarative implementations to coexist within existing imperative system architec-tures. We found that relations were a natural boundary for maintaining the ongoing system state on which the imperative and declarative code was based, and provided an elegant …