---

name: performance-profiling description: Identify performance bottlenecks systematically. Measure before optimizing.

Performance Profiling

Core Principle

Measure first. Optimize second. Verify third.

Never optimize based on intuition. Profile to find actual bottlenecks.

The Process

1. Establish Baseline

Copy# Node.js
node --prof app.js
node --prof-process isolate-*.log > profile.txt

# Browser
Performance tab → Record → Analyze

2. Identify Bottlenecks

Look for:

• Functions with high "self time"
• Unexpected call counts
• Memory allocations in hot paths
• N+1 queries

3. Form Hypothesis

"Function X is slow because Y"

4. Optimize Minimally

One change at a time:

• Caching
• Algorithm improvement
• Batch operations
• Lazy loading

5. Verify Improvement

Compare against baseline. Must be measurably better.

Common Bottlenecks

Tools

Node.js:

• --prof flag
• clinic.js
• 0x flame graphs

Browser:

• DevTools Performance
• Lighthouse
• WebPageTest

Database:

• EXPLAIN ANALYZE
• Query logs
• Connection pool stats

Red Flags

• Optimizing without profiling
• "I think this is slow"
• Premature optimization
• Micro-optimizations in cold paths