DataFusion, an industrial-strength query engine, optimizes SQL and DataFrames queries using various techniques such as Always Optimizations, Engine Specific Optimizations, and heuristics. The optimizer uses cost models to estimate the performance of different plans and chooses the one with the lowest estimated cost. It also considers factors such as join order, access paths, and materialized views in its optimization process. DataFusion's design goals include providing a reasonable default implementation along with extension points to customize behavior, allowing users to tailor the optimizer to their specific needs. The system's modular design and documentation make it an attractive platform for research and development in query engine optimization.