Steno: automatic optimization of declarative queries

Abstract

Declarative queries enable programmers to write data manipulation code without being aware of the underlying data structure implementation. By increasing the level of abstraction over imperative code, they improve program readability and, crucially, create opportunities for automatic parallelization and optimization. For example, the Language Integrated Query (LINQ) extensions to C# allow the same declarative query to process in-memory collections, and datasets that are distributed across a compute cluster. However, our experiments show that the serial performance of declarative code is several times slower than the equivalent hand-optimized code, because it is implemented using run-time abstractions---such as iterators---that incur overhead due to virtual function calls and superfluous instructions.