PostgreSQL Indexing: Why Your Queries Are Slow and How to Fix Them

Always Read the Plan First

Two outcomes:
- `Seq Scan on orders` — reads EVERY row. Add an index.
- `Index Scan using idx_orders_user_id` — fast. Good.
## Rule 1: Index Every Foreign Key

Rule 2: Composite Index for WHERE + ORDER BY

## Rule 3: Partial Indexes

Rule 4: Find Your Slow Queries

## Rule 5: Delete Unused Indexes

**Remember:** Every index speeds up reads but slows INSERT/UPDATE/DELETE. Only index columns you actually filter or sort by.