PostgreSQL Query Optimisation for Django Developers

Finding Slow Queries

Install django-debug-toolbar in development and enable the SQL panel. In production, log queries slower than 100ms using Django's DATABASE logging configuration.

N+1 Queries

The most common Django performance killer. Always use select_related() for ForeignKey and OneToOne fields, and prefetch_related() for ManyToMany and reverse FKs.

Indexes

Add db_index=True on fields used in WHERE, ORDER BY, and JOIN clauses. Use partial indexes and composite indexes for complex query patterns. Run EXPLAIN ANALYZE to confirm the index is being used.

Connection Pooling

Use PgBouncer or django-db-geventpool in production. Without pooling, each Django process opens a new database connection — catastrophic under load.

select_for_update and Transactions

Use select_for_update() with atomic() blocks for race-condition-sensitive operations like inventory updates and payments.