# Django Performance (Django)

> Query optimization, N+1 problem, database indexes, connection pooling, profiling, monitoring

- 24 interview questions
- Senior
- [Interview Questions: Django](https://sharpskill.dev/en/technologies/django/interview-questions.md)

## 1. What is the most common performance issue related to Django ORM queries?

**Answer**

The N+1 problem is the most common performance issue with Django ORM. It occurs when an initial query fetches N objects, then N additional queries are executed to fetch related objects. For example, iterating over articles and accessing their author generates one query per article instead of a single joined query.

## 2. Which method should be used to solve the N+1 problem with a ForeignKey relationship?

**Answer**

select_related() is the appropriate method to solve the N+1 problem with ForeignKey and OneToOneField relationships. It performs a SQL join and fetches related objects in a single query. prefetch_related() is used for ManyToMany relationships or reverse relations (ForeignKey reverse).

## 3. When should prefetch_related() be used instead of select_related()?

**Answer**

prefetch_related() is designed for ManyToMany relationships and reverse relations (ForeignKey reverse). Unlike select_related() which performs a SQL join, prefetch_related() executes a separate query and performs the join in Python. This avoids data duplication that would occur with a SQL join on many-to-many relationships.

## 21 more questions available

- How to use Prefetch() to customize prefetch_related() queries?
- What is the main benefit of adding a database index on a field?

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## Other Django interview topics

- [Python Basics](https://sharpskill.dev/en/technologies/django/interview-questions/python-basics.md): 25 questions, Junior
- [Python OOP](https://sharpskill.dev/en/technologies/django/interview-questions/python-oop.md): 20 questions, Junior
- [Django Fundamentals](https://sharpskill.dev/en/technologies/django/interview-questions/django-fundamentals.md): 20 questions, Junior
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- [Django Templates](https://sharpskill.dev/en/technologies/django/interview-questions/django-templates.md): 18 questions, Junior
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- [Settings & Production Configuration](https://sharpskill.dev/en/technologies/django/interview-questions/django-settings-configuration.md): 22 questions, Senior
- [Observability & Monitoring](https://sharpskill.dev/en/technologies/django/interview-questions/django-observability.md): 24 questions, Senior

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