The same query, the same index, and a different execution plan depending on which customer it is run for. The optimiser switching strategies at a selectivity threshold is…
A test asserting fewer than ten queries, written in 2023, failing in July because a legitimate feature added an eleventh. A bound that fails on a legitimate change…
Two years of a rotating slow query log, aggregated for the first time. Ranking by total time rather than by per-call time is what makes the list actionable,…
A key inside a JSON column filtered on four hundred thousand times a day, promoted without changing any application code. The optimiser matching a functional expression to a…
An index created for a reporting query, and the report replaced by a projection four weeks afterwards. An index nobody reads costs write throughput and buffer pool on…