Feat cache residual evaluator #2695
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Fixes apache#2147 - Implement ResidualEvaluatorCache with LRU eviction and thread safety - Cache evaluators by partition spec, expression, case sensitivity, and schema - Fix mypy type annotations and add type ignore for cachetools decorator
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| cached = _residual_evaluator_cache.get(spec, expr, case_sensitive, schema) | ||
| if cached is not None: | ||
| return cached |
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Why not use the build in LRU cache? https://docs.python.org/3/library/functools.html#functools.lru_cache
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Hi @Fokko 👋 ! We certainly could try to simplify this — my main motivation for the current approach was to build something that felt more extensible, more readable (so contributors don’t have to dig too deep to understand what’s going on), and that gives users a bit more control.
That said, when I considered switching to functools.lru_cache for residual evaluator creation, it looked like it would actually require more work to avoid a custom cache. Specifically, making the cache keys hashable while still passing the spec, expr, and schema objects — which aren’t inherently hashable — seemed tricky. I would have needed helper functions to produce stable key representations, and potentially to check the hashability of PartitionSpec, just to ensure caching didn’t break evaluator construction.
I’m definitely open to simplifying this if you think that’s the right direction. Let me know your thoughts!
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Closes #2147
Rationale for this change
For queries, the same combinations of (partition spec, expression, case sensitivity, schema) are evaluated repeatedly, causing unnecessary computational overhead and increased query latency.
Are these changes tested?
Yes, using the existing test cases as they seemed sufficient for the changes.
Are there any user-facing changes?
No.