The query had been taking 60 seconds for two years. Everyone had accepted it.
When I joined AfriCred: missing composite indexes, unnecessary full-table scans, three subqueries collapsible into two joins, and a schema decision from year one forcing a cross-table recalculation on every page load.
The rewritten query ran in 4 seconds. The reaction from the team was disbelief.
56 saved seconds per query. Hundreds per day. Compounded across two years of staff time. The slow query had not been a technical problem. It had been a business tax.
Optimise the slow queries. The ROI is almost always immediate.
— Dick Bassey | DevDick | 2022