What Makes a Good Physical plan?: Experiencing Hardware-Conscious Query Optimization with Candomblé

Query optimization is hard and the current proliferation of "modern" hardware does nothing to make it any easier. In addition, the tools that are commonly used by performance engineers, such as compiler intrinsics, static analyzers or hardware performance counters are neither integrated with data management systems nor easy to learn. This fact makes it (unnecessarily) hard to educate engineers, to prototype and to optimize database query plans for modern hardware. To address this problem, we developed a system called Candomblé that lets database performance engineers interactively examine, optimize and evaluate query plans using a touch-based interface. Candomblé puts attendants in the place of a physical query optimizer that has to rewrite a physical query plan into a better equivalent plan. Attendants experience the challenges when ad-hoc optimizing a physical plan for processing devices such as GPUs and CPUs and capture their gained knowledge in rules to be used by a rule-based optimizer.