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name: performance-optimizer description: Use when analyzing code for performance bottlenecks, optimizing slow queries, reducing memory usage, or improving application speed. Identifies N+1 queries, inefficient algorithms, and caching opportunities. allowed-tools: Read, Grep, Glob, Bash model: sonnet

Performance Optimizer Skill

Purpose

Analyzes code for performance issues and provides optimization recommendations including:

• Database query optimization
• Algorithm efficiency improvements
• Memory usage reduction
• Caching strategies
• Lazy loading opportunities

When to Use

This skill should be invoked when:

• Application is running slowly
• High memory consumption detected
• Database queries taking too long
• Need to optimize before scaling
• Performance regression after changes
• Preparing for production deployment

Process

1. Identify Bottlenecks

   • Profile critical code paths
   • Analyze database queries
   • Check loop efficiency
   • Review memory allocations
   • Examine API calls

2. Analyze Root Causes

   • N+1 query problems
   • Missing database indexes
   • Inefficient algorithms (O(n²) vs O(n log n))
   • Unnecessary re-renders (React/Vue)
   • Large bundle sizes
   • Synchronous blocking operations

3. Recommend Optimizations

   • Add database indexes
   • Implement query batching
   • Use more efficient algorithms
   • Add caching (Redis, memory)
   • Implement lazy loading
   • Use pagination
   • Optimize images/assets

4. Estimate Impact

   • High impact: 10x+ improvement
   • Medium impact: 2-10x improvement
   • Low impact: <2x improvement

Output Format

Performance Analysis Report

🔴 Critical Issues (High Impact)

• [Location] - [Issue description]
  • Current: [performance metric]
  • Expected: [improved metric]
  • Fix: [specific solution]

🟡 Optimization Opportunities (Medium Impact)

• [Location] - [Issue description]
  • Impact: [estimated improvement]
  • Fix: [specific solution]

🟢 Minor Improvements (Low Impact)

• [Location] - [Issue description]
  • Fix: [specific solution]

📊 Metrics

• Queries analyzed: X
• Potential speedup: Xx
• Memory reduction: X%

Best Practices

• Profile before optimizing (measure first)
• Focus on high-impact changes first
• Consider readability vs performance tradeoffs
• Test optimizations with realistic data
• Monitor production metrics
• Document why optimizations were made

Examples

Example 1: N+1 Query Detection

Input: "Why is this API endpoint slow?"

Analysis:

Copy// BEFORE: N+1 query problem
async function getUsers() {
  const users = await User.findAll();
  for (const user of users) {
    user.posts = await Post.findAll({ userId: user.id });
  }
  return users;
}

Output:

Copy🔴 Critical: N+1 Query Pattern
Location: api/users.js:15-19
Current: 1 + N queries (101 queries for 100 users)
Expected: 2 queries total
Impact: ~50x faster with large datasets

Fix:
async function getUsers() {
  const users = await User.findAll({
    include: [{ model: Post }]
  });
  return users;
}

Example 2: Algorithm Optimization

Input: "This search is too slow"

Analysis:

Copy// BEFORE: O(n²) nested loop
function findDuplicates(arr) {
  const duplicates = [];
  for (let i = 0; i < arr.length; i++) {
    for (let j = i + 1; j < arr.length; j++) {
      if (arr[i] === arr[j]) duplicates.push(arr[i]);
    }
  }
  return duplicates;
}

Output:

Copy🟡 Medium Impact: Inefficient Algorithm
Location: utils/search.js:23-30
Current: O(n²) - 10,000ms for 1000 items
Expected: O(n) - 10ms for 1000 items
Impact: 1000x faster

Fix:
function findDuplicates(arr) {
  const seen = new Set();
  const duplicates = new Set();
  for (const item of arr) {
    if (seen.has(item)) duplicates.add(item);
    seen.add(item);
  }
  return Array.from(duplicates);
}

Example 3: React Re-render Optimization

Input: "Component re-renders too often"

Analysis:

Copy// BEFORE: Creates new object every render
function UserList({ users }) {
  const config = { sortBy: 'name', order: 'asc' };
  return <Table data={users} config={config} />;
}

Output:

Copy🟢 Low Impact: Unnecessary Re-renders
Location: components/UserList.jsx:12-14
Impact: Reduces re-renders by ~60%

Fix:
const config = { sortBy: 'name', order: 'asc' };
function UserList({ users }) {
  return <Table data={users} config={config} />;
}
// Or use useMemo if config needs to be computed

Error Handling

• No performance issues found: Confirm with profiling data
• Need metrics: Request actual performance measurements
• Optimization premature: Advise profiling first
• Breaking change risk: Warn about potential issues

Notes

• Always profile before and after optimizations
• Consider tradeoffs: speed vs readability vs maintenance
• Some optimizations are language/framework specific
• Database optimizations often have highest impact
• Don't optimize without measuring
• Production data may differ from development