A cache entry expiring under load means every concurrent request recomputes it, and a lock makes them queue instead. One request recomputes slightly early while everybody else is…
A process holding thousands of idle connections is not what a request-per-process model is for, and a small binary beside it is a smaller change than a rewrite.…
A deleted_at column means every query filters on it forever, and the rows stay in the index, in the buffer pool and in the backup. PostgreSQL’s partial index…
The append-only file rewrite used to fork the process and rewrite everything into one file, which doubled memory at the worst possible moment. The fork-and-copy behaviour was the…
A CI runner is shared, throttled and occasionally slow, so any assertion about wall-clock time fails eventually for reasons unrelated to the code. Query counts and memory are…