Window Function Optimization: Co-Evaluation and Other Techniques

2026-08-06

AI Summary

Existing approaches to window function optimization suffer from stringent applicability conditions and limited generalizability, lacking a unified reasoning framework. This work proposes the first systematic inference framework for window function optimization, which derives algebraically equivalent transformations that can be safely applied by leveraging frame analysis, partition analysis, and a novel co-evaluation strategy. This enables predicate pushdown even in the presence of dependencies on window results. Implemented in an open-source query engine, the framework consistently preserves or improves performance, achieving speedups of up to 40.7× on common queries, with gains becoming more pronounced as data scale increases.

Abstract

Window functions are among the most expressive features of modern SQL. Surprisingly, relatively little has been written about their optimization. Some techniques exist, such as pushing predicates through a window under ideal conditions, but known optimizations no longer apply when those conditions are even slightly unmet. We show that these limitations are not fundamental, but persist because a reasoning framework for window function optimization has been missing. We provide such a framework, introducing techniques we call Frame Analysis, Partition Analysis, and a new execution strategy called Co-Evaluation. These clarify when and how optimizations can be applied. Co-Evaluation, in particular, allows early evaluation of predicates even when they depend on the window function's result. We present each technique and organize the results as a table of algebraic equivalences for window functions. We test these optimizations in an open-source engine, where they never hurt performance and make certain common queries up to 40.7 times faster, with larger tables yielding larger gains.

Problem

• window functions
• query optimization
• SQL
• predicate pushdown
• algebraic equivalences

Innovation

• Window Function Optimization
• Co-Evaluation
• Frame Analysis
• Partition Analysis
• Algebraic Equivalences