PostgreSQL
Query plans, indexes and the planner’s decision procedure. Every piece here has a runnable reproduction.
A benchmark with no network in it measures the floor
A cascade delete that took seven minutes in production is a barely-visible win on my laptop. Measuring the per-statement cost showed why, and why a local number here is a floor rather than the size of the fix.
18 September 2026 · with a runnable benchmark
An array parameter of the wrong width
The same id list, one type wider than the column, costs two hundred times as much. PostgreSQL explains both statements with the identical plan, and EXPLAIN reports the same buffers.
18 September 2026 · with a runnable benchmark
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