# Performance and Scaling — Django / FastAPI

Source: https://www.skillbyai.com/en/django-fastapi/d-perf

> Measure, cache, offload.

## Usual bottlenecks

Most slow Python web apps are slow because of the **database**: N+1 queries, missing indexes, large result sets. Fix those first, then add **caching** (Django's cache framework with Redis, HTTP caching headers), move slow work to **background jobs** (Celery, RQ, Dramatiq, or arq for async), paginate lists, and use connection pooling. Profile with real data and load tests before rewriting anything for speed.

## A performance triage order

Work down the list.

```text
1 measure: slow query log, APM traces, Debug Toolbar / query counts
2 database: indexes, select_related/prefetch_related, pagination
3 caching: per-view or per-object caches in Redis; HTTP cache headers
4 background jobs: emails, reports, image processing out of the request
5 concurrency: workers, async for I/O-bound endpoints
6 only then: rewrite hot paths or split services
```

## Fix queries before adding servers

More workers multiply the load of inefficient queries on the database.

**Quiz:** What is the most common cause of slow Django or FastAPI endpoints?

- [ ] Python syntax
- [ ] The choice of web framework
- [x] Inefficient database access
- [ ] Too few comments

*Answer:* Inefficient database access. Measure the database first.