Torin Deep Dive: Lazy Evals in GPU-Native SQL Engine

Starburst’s Torin GPU-native SQL engine uses NVIDIA GPUs and cuDF to execute SQL operators in columnar batches, gaining performance from massively parallel evaluation while preserving standard SQL semantics. The post examines the challenge of implementing lazy evaluation for expressions such as AND when the right-hand side may fail, as in guarded division by zero cases, since naïve eager GPU evaluation would process every row and raise errors even where SQL short-circuit behavior would avoid them. Torin selects among three execution strategies based on an expression’s failure characteristics: eager evaluation for infallible expressions, NULL masking for expressions made safe by NULL inputs, and filter-and-scatter processing for cases where only evaluating active rows can prevent errors. Expression fallibility is inferred during compilation, allowing the engine to use the cheapest correct method and skip unnecessary work when no rows require a conditional path. Torin centralizes this behavior through IF expressions, rewriting AND, OR, COALESCE, and related constructs with an internal LET mechanism that prevents repeated computation, while grouping safe adjacent predicates to retain the fastest eager GPU path for common comparison-only filters.

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