A form that saves and redirects to a page that reads, with a replica that is 200 ms behind and a redirect that takes 40. Sticky-per-request covers the…
A search cluster indexing 4,000 rows to support an admin lookup by name, added because “search” was in the requirement. A prefix match on an indexed column is…
An index containing every column the query touches means the table is never read, and the plan says Using index. The column order is the design: equality predicates…
The DESC keyword in an index definition was parsed and ignored until 8.0, so mixed-direction sorts always needed a filesort. This only matters for mixed directions — a…
Four years of nightly backups, never restored, and the first restore produced a database missing one table. The exclusion was reasonable when it was added and became wrong…