Bugs we found in DuckDB, ClickHouse, and NumPy aggregate functions

What we're building

We have been developing writePath over the past year focused on providing customers with:

1. Sub-millisecond aggregations over the first or last N rows of their data with no pre-computation
2. Precise aggregation functions validated against reference implementations and exact math
3. A simple AWS Marketplace experience allowing control through APIs

What we found

During development we used reference implementations from vendors and packages such as DuckDB, ClickHouse, and NumPy to validate aggregate correctness.

We found bugs within the reference implementations falling into one of 3 main categories: Rounding, Range, and Logic.

Category	Reference implementation bug	How writePath addresses it
Rounding	Digits rounded during accumulation are lost	Values are accumulated exactly and rounded once at the end
Range	Numbers exceed type constraints resulting in overflow or wraparound	Integers stay integers and intermediate results never overflow when the true answer fits
Logic	The wrong rule is applied for constant data, infinities, zero or negative weights, or empty input	Every edge case has a defined rule that is documented per function and validated against reference implementations and exact math

How we report bugs

Since these are not security bugs, our approach is to submit each bug to the vendor through proper channels and then post our findings here.

After each submission and post, we will add another entry to the table at the bottom of this post.

About Us

writePath is an AWS Marketplace SaaS for sub-millisecond aggregations over the first or last N rows of your data with no pre-computation. It offers 65 high-precision aggregation functions tested against reference implementations.

www.thewritepath.net

All Vendor Bugs

Vendor	Function	Bug Submission Link	Blog Post	Date
DuckDB	favg	duckdb/duckdb#27961	DuckDB favg returns the wrong average when values differ greatly in magnitude	October 27, 2026