Custom user model with AbstractUser in Django - Performance & Optimization

Performance: Custom user model with AbstractUser

MEDIUM IMPACT

This affects the initial page load speed and authentication-related interactions by changing how user data is loaded and managed.

Extending user data with a custom user model

Django

from django.contrib.auth.models import AbstractUser
from django.db import models

class CustomUser(AbstractUser):
    extra_field = models.CharField(max_length=100)

# Set AUTH_USER_MODEL = 'app.CustomUser' in settings.py

Extending AbstractUser keeps all user data in one table, reducing joins and speeding up queries.

📈 Performance GainSingle database query per user load, reducing authentication latency by up to 50ms

Extending user data with a custom user model

Django

from django.contrib.auth.models import User
from django.db import models

# Adding profile info via separate model with OneToOneField
class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    extra_field = models.CharField(max_length=100)

This pattern causes extra database joins on every user query, increasing query time and slowing authentication-related views.

📉 Performance CostTriggers multiple database queries per user load, increasing response time by 50-100ms depending on DB size

Performance Comparison

Pattern	Database Queries	Joins	Query Latency	Verdict
Separate Profile Model	2+ queries per user	1 join per user	Higher latency due to joins	[X] Bad
CustomUser extends AbstractUser	1 query per user	No joins needed	Lower latency, faster auth	[OK] Good

Rendering Pipeline

Custom user models affect server-side data fetching and authentication logic, which impacts how fast user data is ready for rendering.

→Data Fetching

→Server Response

→Client Rendering

⚠️ BottleneckDatabase query time during authentication and user data retrieval

Core Web Vital Affected

INP

This affects the initial page load speed and authentication-related interactions by changing how user data is loaded and managed.

Optimization Tips

1Use AbstractUser to keep user data in one table and avoid joins.

2Add database indexes on custom user fields to speed queries.

3Avoid separate profile models that cause extra database joins during authentication.

Performance Quiz - 3 Questions

Why is extending AbstractUser better for performance than using a separate profile model?

A It automatically caches user data in the browser.

B It reduces the number of database queries by storing all user data in one table.

C It eliminates the need for authentication.

D It uses less memory on the client side.

DevTools: Network

How to check: Open DevTools, go to Network tab, filter for authentication API calls, and inspect timing details for user data requests.

What to look for: Look for multiple sequential requests or long response times indicating extra queries or joins slowing down user data loading.