optimizing-performance

# Optimizing Performance ### When to Load - **Trigger**: Diagnosing slowness, profiling, caching strategies, reducing load times, bundle size optimization - **Skip**: Correctness-focused work where performance is not a concern ## Performance Optimization Workflow Copy this checklist and track progress: ``` Performance Optimization Progress: - [ ] Step 1: Measure baseline performance - [ ] Step 2: Identify bottlenecks - [ ] Step 3: Apply targeted optimizations - [ ] Step 4: Measure again and compare - [ ] Step 5: Repeat if targets not met ``` **Critical Rule**: Never optimize without data. Always profile before and after changes. ## Step 1: Measure Baseline ### Profiling Commands ```bash # Node.js profiling node --prof app.js node --prof-process isolate*.log > profile.txt # Python profiling python -m cProfile -o profile.stats app.py python -m pstats profile.stats # Web performance lighthouse https://example.com --output=json ``` ## Step 2: Identify Bottlenecks ### Common Bottleneck Categories | Category | Symptoms | Tools | | -------- | -------------------------------- | ------------------------------- | | CPU | High CPU usage, slow computation | Profiler, flame graphs | | Memory | High RAM, GC pauses, OOM | Heap snapshots, memory profiler | | I/O | Slow disk/network, waiting | strace, network inspector | | Database | Slow queries, lock contention | Query analyzer, EXPLAIN | ## Step 3: Apply Optimizations ### Frontend Optimizations **Bundle Size:** ```javascript // ❌ Import entire library import _ from "lodash"; // ✅ Import only needed functions import debounce from "lodash/debounce"; // ✅ Use dynamic imports for code splitting const HeavyComponent = lazy(() => import("./HeavyComponent")); ``` **Rendering:** ```javascript // ❌ Render on every parent update function Child({ data }) { return <ExpensiveComponent data={data} />; } // ✅ Memoize when props don't change const Child = memo(function Child({ data }) { return <ExpensiveComponent data={data} />; }); // ✅ Use useMemo for expensive computations const processed = useMemo(() => expensiveCalc(data), [data]); ``` **Images:** ```html <!-- ❌ Unoptimized --> <img src="large-image.jpg" /> <!-- ✅ Optimized --> <img src="image.webp" srcset="image-300.webp 300w, image-600.webp 600w" sizes="(max-width: 600px) 300px, 600px" loading="lazy" decoding="async" /> ``` ### Backend Optimizations **Database Queries:** ```sql -- ❌ N+1 Query Problem SELECT * FROM users; -- Then for each user: SELECT * FROM orders WHERE user_id = ?; -- ✅ Single query with JOIN SELECT u.*, o.* FROM users u LEFT JOIN orders o ON u.id = o.user_id; -- ✅ Or use pagination SELECT * FROM users LIMIT 100 OFFSET 0; ``` **Caching Strategy:** ```javascript // Multi-layer caching const getUser = async (id) => { // L1: In-memory cache (fastest) let user = memoryCache.get(`user:${id}`); if (user) return user; // L2: Redis cache (fast) user = await redis.get(`user:${id}`); if (user) { memoryCache.set(`user:${id}`, user, 60); return JSON.parse(user); } // L3: Database (slow) user = await db.users.findById(id); await redis.setex(`user:${id}`, 3600, JSON.stringify(user)); memoryCache.set(`user:${id}`, user, 60); return user; }; ``` **Async Processing:** ```javascript // ❌ Blocking operation app.post("/upload", async (req, res) => { await processVideo(req.file); // Takes 5 minutes res.send("Done"); }); // ✅ Queue for background processing app.post("/upload", async (req, res) => { const jobId = await queue.add("processVideo", { file: req.file }); res.send({ jobId, status: "processing" }); }); ``` ### Algorithm Optimizations ```javascript // ❌ O(n²) - nested loops 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; } // ✅ O(n) - hash map 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 [...duplicates]; } ``` ## Step 4: Measure Again After applying optimizations, re-run profiling and compare: ``` Comparison Checklist: - [ ] Run same profiling tools as baseline - [ ] Compare metrics before vs after - [ ] Verify no regressions in other areas - [ ] Document improvement percentages ``` ## Performance Targets ### Web Vitals | Metric | Good | Needs Work | Poor | | ------ | ------- | ---------- | ------- | | LCP | < 2.5s | 2.5-4s | > 4s | | INP | < 200ms | 200-500ms | > 500ms | | CLS | < 0.1 | 0.1-0.25 | > 0.25 | | TTFB | < 800ms | 800ms-1.8s | > 1.8s | ### API Performance | Metric | Target | | ----------- | ------- | | P50 Latency | < 100ms | | P95 Latency | < 500ms | | P99 Latency | < 1s | | Error Rate | < 0.1% | ## Validation After optimization, validate results: ``` Performance Validation: - [ ] Metrics improved from baseline - [ ] No functionality regressions - [ ] No new errors introduced - [ ] Changes are sustainable (not one-time fixes) - [ ] Performance gains documented ``` If targets not met, return to Step 2 and identify remaining bottlenecks.