Abstract

Data processing systems face the challenge of supporting increasingly diverse workloads efficiently. At the same time, they are already bloated with internal complexity, and it is not clear how new hardware can be supported sustainably. In this paper, we aim to resolve these issues by proposing a unified abstraction layer based on declarative sub-operators in addition to relational operators. By exposing this layer to users, they can express their non-relational workloads declaratively with sub-operators. Furthermore, the proposed sub-operators decouple the semantic implementation of operators from the efficient imperative implementation, reducing the implementation complexity for relational operators. Finally, through fine-grained automatic optimizations, the declarative sub-operators allow for automatic morsel-driven parallelism. We demonstrate the benefits not only by providing a specific set of sub-operators but also implementing them in a compiling query engine. With thorough evaluation and analysis, we show that we can support a richer set of workloads while retaining the development complexity low and being competitive in performance even with specialized systems.

Abstract

Since its invention, data-centric code generation has been adopted for query compilation by various database systems in academia and industry. These database systems are fast but maximize performance at the expense of developer friendliness, flexibility, and extensibility. Recent advances in the field of compiler construction identified similar issues for domain-specific compilers and introduced a solution with MLIR, a generic infrastructure for domain-specific dialects.
We propose a layered query compilation stack based on MLIR with open intermediate representations that can be combined at each layer. We further propose moving query optimization into the query compiler to benefit from the existing optimization infrastructure and make cross-domain optimization viable. With LingoDB, we demonstrate that the used approach significantly decreases the implementation effort and is highly flexible and extensible. At the same time, LingoDB achieves high performance and low compilation latencies.