The orders page went from 20 ms to 4 seconds

• A customer’s order list loaded instantly at launch and now takes ~4 s.
• No code has changed in months.
• The orders table has grown from ~5,000 rows to ~3,000,000.

EXPLAIN ANALYZE SELECT id, total, created_at FROM orders
  WHERE user_id = 17 ORDER BY created_at DESC LIMIT 20;

Limit  (actual time=3980..3980 rows=20 loops=1)
  ->  Sort  (actual rows=142 loops=1)
        Sort Method: quicksort
        ->  Seq Scan on orders  (actual rows=142 loops=1)
              Filter: (user_id = 17)
              Rows Removed by Filter: 2999858