performance-optimization

Performance Optimization

Overview

Measure first, optimize second. This guide covers profiling techniques and optimization strategies.

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Profiling First

The Golden Rule

1. Don't optimize prematurely
2. Measure before optimizing
3. Optimize the biggest bottleneck first
4. Measure again to verify improvement

CPU Profiling (Node.js)

// Using Node.js built-in profiler
// Start with: node --prof app.js
// Process: node --prof-process isolate-*.log > profile.txt

// Or use clinic.js
// npm install -g clinic
// clinic doctor -- node app.js
// clinic flame -- node app.js

// Programmatic profiling
import { performance, PerformanceObserver } from 'perf_hooks';

const obs = new PerformanceObserver((items) => {
  items.getEntries().forEach((entry) => {
    console.log(`${entry.name}: ${entry.duration}ms`);
  });
});
obs.observe({ entryTypes: ['measure'] });

performance.mark('start');
await expensiveOperation();
performance.mark('end');
performance.measure('expensive-op', 'start', 'end');

Memory Profiling

// Check memory usage
console.log(process.memoryUsage());
// {
//   rss: 30000000,      // Resident Set Size - total memory
//   heapTotal: 7000000, // V8 heap total
//   heapUsed: 5000000,  // V8 heap used
//   external: 800000    // C++ objects bound to JS
// }

// Take heap snapshot
const v8 = require('v8');
const fs = require('fs');

const snapshotFile = `heap-${Date.now()}.heapsnapshot`;
const snapshot = v8.writeHeapSnapshot(snapshotFile);
// Open in Chrome DevTools Memory tab

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Database Optimization

Query Optimization

-- ❌ Slow: SELECT * and no index
SELECT * FROM orders WHERE user_id = 123;

-- ✅ Better: Select only needed columns, with index
CREATE INDEX idx_orders_user_id ON orders(user_id);
SELECT id, total, status FROM orders WHERE user_id = 123;

-- ❌ N+1 query problem
-- For each user, query their orders (100 users = 101 queries)
SELECT * FROM users;
SELECT * FROM orders WHERE user_id = 1;
SELECT * FROM orders WHERE user_id = 2;
...

-- ✅ Single query with JOIN
SELECT u.*, o.* FROM users u
LEFT JOIN orders o ON u.id = o.user_id;

-- Or batch loading
SELECT * FROM orders WHERE user_id IN (1, 2, 3, ...);