Optimisation of language-integrated queries by query unnesting

摘要

Native functional-style querying extensions for programming languages (e.g., LINQ or Java 8 streams) are widely considered as declarative. However, their very limited degree of optimisation when dealing with local collection processing contradicts this statement. We show that developers constructing complex LINQ queries or combining queries expose themselves to the risk of severe performance deterioration. For an inexperienced programmer, a way of getting an appropriate query form can be too complicated. Also, a manual query transformation is justified by the need of improving performance, but achieved at the expense of reflecting an actual business goal. As a result, benefits from a declarative form and an increased level of abstraction are lost.