DuckDB 1.5 ships a wire protocol called Quack. We re-implemented it in pure Rust, turned SQE into both server and client, and proved you can JOIN an Iceberg table with a remote DuckDB table in a single SELECT. Two waves of bugs, one federated query.
ReadWe started with a markdown table tracking which DuckDB types we could round-trip. The table became the roadmap. DECIMAL, LIST, STRUCT, MAP, ARRAY, ENUM, UNION each got their own MR. The surprises came from how DuckDB models the relationships: MAP is LIST<STRUCT>, UNION is STRUCT with a tag field, and DECIMAL packs four widths into one logical type.
ReadTen sub-MRs in a day. The wire format, the fixture-driven debugging loop, and two bugs that the C++ reference encoder ships without telling you: WriteListWithDefault elision, and uninitialised bytes at NULL VARCHAR positions.
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