rails-performance-patterns

# Rails Performance Patterns Skill

Automatically detects performance issues and suggests optimizations.

## What This Skill Does

**Automatic Detection:**
- N+1 query problems (missing eager loading)
- Missing database indexes on foreign keys
- Inefficient query patterns
- Large result sets without pagination

**When It Activates:**
- Model files with associations modified
- Controller actions that query models
- Iteration over associations detected

## Key Checks

### 1. N+1 Query Detection

**Problem Pattern:**
```ruby
# app/controllers/posts_controller.rb
def index
  @posts = Post.all  # 1 query
  @posts.each do |post|
    puts post.author.name  # N queries (one per post)
  end
end
```

**Skill Output:**
```
⚠️  Performance: Potential N+1 query
Location: app/controllers/posts_controller.rb:15
Issue: Accessing 'author' association in loop without eager loading

Fix: Add includes to eager load:
@posts = Post.includes(:author).all
```

**Solution:**
```ruby
def index
  @posts = Post.includes(:author).all  # 2 queries total
end
```

### 2. Missing Indexes

**Checks:**
- Foreign keys have indexes
- Commonly queried columns indexed
- Unique constraints have indexes

**Example:**
```ruby
# db/migrate/xxx_create_posts.rb
create_table :posts do |t|
  t.references :user  # ✅ Auto-creates index
  t.string :slug      # ❌ Missing index if queried often
end
```

**Skill Output:**
```
⚠️  Performance: Missing index recommendation
Location: app/models/post.rb:5
Issue: slug column used in where clauses without index

Add migration:
add_index :posts, :slug, unique: true
```

### 3. Pagination Missing

**Problem:**
```ruby
def index
  @products = Product.all  # ❌ Loads all 100k+ products
end
```

**Skill Output:**
```
⚠️  Performance: Large result set without pagination
Location: app/controllers/products_controller.rb:10
Issue: Loading all Product records (estimated 100k+ rows)

Recommendation: Add pagination
# Use kaminari or pagy
@products = Product.page(params[:page]).per(20)
`