---
name: performance-reviewer
description: Analyze Rails code for performance issues, optimize queries, identify bottlenecks, and ensure scalability. Apply after implementing features or when performance concerns arise.
allowed-tools: Read Grep Glob Bash
---

# Rails Performance Review

**Audience:** Rails developers reviewing code for performance issues
**Goal:** Identify N+1 queries, missing indexes, memory issues, and scalability bottlenecks

## Analysis Framework

Check all areas systematically. See [references/patterns.yaml](references/patterns.yaml) for anti-patterns and fixes.

| Area | What to Check |
|------|---------------|
| **Database** | N+1 queries, missing indexes, inefficient queries, counter caches |
| **Algorithmic** | Time complexity, O(n^2) or worse without justification |
| **Memory** | Batch processing for large collections, memory-efficient loading |
| **Caching** | Memoization opportunities, Rails.cache for expensive computations |
| **Background Jobs** | Long-running tasks that should be async |
| **Locks** | Transaction scopes, lock duration, external calls in transactions |
| **Defensive** | strict_loading, query timeouts |

## Performance Benchmarks

- No algorithms worse than O(n log n) without justification
- All queried columns must have indexes
- API responses under 200ms
- Collections processed in batches (1000 items max)

## Verification Commands

```bash
# Check for missing indexes in schema
grep -E "(belongs_to|has_many)" app/models/*.rb | grep -v "optional:"

# Find potential N+1 queries
grep -rn "\.each.*\." app/ --include="*.rb" | grep -v find_each

# Check slow query log (if enabled)
tail -100 log/development.log | grep "Load"
```

## Output Format

```markdown
## Performance Summary
[High-level assessment]

## Critical Issues
| Issue | Impact | Solution |
|-------|--------|----------|
| [description] | [current + at scale] | [specific fix] |

## Scalability Assessment
- At 10x data: [projection]
- At 100x data: [projection]

## Recommended Actions
1. [Highest impact fix]
2. [Next priority]
```