Your query is slow. You check: the database is fine. Connections are fine. The query is just... slow. You look at the query: SELECT * FROM orders WHERE user_id = 123 Enter fullscreen mode Exit fullscreen mode Seems simple. Why is it slow? Because there's no index on user_id . The database scans every row to find matching ones. With a million rows, that's a million comparisons. Add an index. Instant 100x speedup. The Index An index is a lookup table. Without index: SELECT * FROM orders WHERE user_id = 123 → Database scans all 1 M rows → Finds matches → Returns results Enter fullscreen mode Exit fullscreen mode With index: SELECT * FROM orders WHERE user_id = 123 → Index lookup : user_id = 123 → row IDs [ 5 , 12 , 99 , ...] → Fetch those rows → Returns results Enter fullscreen mode Exit fullscreen mode Index is pre-sorted. Lookup is instant.…