# Django Perf Review

Django performance code review.

- Repository: https://github.com/getsentry/skills (1107 stars)
- Category: Data and ML
- License: LICENSE
- Last updated: 2026-10-26
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add getsentry/skills --skill django-perf-review -g -a claude-code -y`
Codex: `npx skills add getsentry/skills --skill django-perf-review -g -a codex -y`
Cursor: `npx skills add getsentry/skills --skill django-perf-review -g -a cursor -y`
Gemini CLI: `npx skills add getsentry/skills --skill django-perf-review -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add getsentry/skills`

## Description

Django performance code review. Use when asked to "review Django performance", "find N+1 queries", "optimize Django", "check queryset performance", "database performance", "Django ORM issues", or audit Django code for performance problems.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Django Performance Review

Review Django code for **validated** performance issues. Research the codebase to confirm issues before reporting. Report only what you can prove.

## Review Approach

1. **Research first** - Trace data flow, check for existing optimizations, verify data volume
2. **Validate before reporting** - Pattern matching is not validation
3. **Zero findings is acceptable** - Don't manufacture issues to appear thorough
4. **Severity must match impact** - If you catch yourself writing "minor" in a CRITICAL finding, it's not critical. Downgrade or skip it.

## Impact Categories

Issues are organized by impact. Focus on CRITICAL and HIGH - these cause real problems at scale.

| Priority | Category | Impact |
|----------|----------|--------|
| 1 | N+1 Queries | **CRITICAL** - Multiplies with data, causes timeouts |
| 2 | Unbounded Querysets | **CRITICAL** - Memory exhaustion, OOM kills |
| 3 | Missing Indexes | **HIGH** - Full table scans on large tables |
| 4 | Write Loops | **HIGH** - Lock contention, slow requests |
| 5 | Inefficient Patterns | **LOW** - Rarely worth reporting |

---

## Priority 1: N+1 Queries (CRITICAL)

**Impact:** Each N+1 adds `O(n)` database round trips. 100 rows = 100 extra queries. 10,000 rows = timeout.

### Rule: Prefetch related data accessed in loops

Validate by tracing: View → Queryset → Template/Serializer → Loop access

```python
# PROBLEM: N+1 - each iteration queries profile
def user_list(request):
    users = User.objects.all()
    return render(request, 'users.html', {'users': users})

# Template:
# {% for user in users %}
#     {{ user.profile.bio }}  ← triggers query per user
# {% endfor %}

# SOLUTION: Prefetch in view
def user_list(request):
    users = User.objects.select_related('profile')
    return render(request, 'users.html', {'users': users})
```

### Rule: Prefetch in serializers, not just views

DRF serializers accessing related fields cause N+1 if queryset isn't optimized.

The rest: https://github.com/getsentry/skills/blob/HEAD/skills/django-perf-review/SKILL.md