Query Optimizer as a Service: An Idea Whose Time Has Come

Query optimization is a critical technology that is common across all modern data processing systems. However, it is traditionally implemented in silos and is deeply embedded in different systems. Furthermore, over the years, query optimizers have become less understood and rarely touched pieces of code that are brittle to changes and very expensive to maintain, thus slowing down the pace of innovation. In this paper, we argue that it is time to think of query optimizer as a service in modern cloud architectures. Such a design can help build a common set of well-maintained optimizations that are externalized from the query engines and that could be learned and improved using the large workloads present in modern clouds. We present, Oasis, a reference architecture for query optimizer as a service and describe our success in deploying the early version of it in Cosmos. Finally, we discuss the risks and responsibilities involved with Oasis to ensure it is a win-win for everyone.