# Jeremylongshore Claude Code Plugins Plus Skills Replit Performance Tuning > Replit Performance Tuning - Skill: `tomevault-io/jeremylongshore-claude-code-plugins-plus-skills-replit-perfo` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/jeremylongshore-claude-code-plugins-plus-skills-replit-perfo` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/jeremylongshore-claude-code-plugins-plus-skills-replit-perfo/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/jeremylongshore-claude-code-plugins-plus-skills-replit-perfo --- # Replit Performance Tuning ## Overview Optimize Replit app performance across the entire lifecycle: cold start reduction, Nix environment caching, build speed, runtime memory management, and deployment configuration. Replit containers have resource limits — efficient usage is critical. ## Prerequisites - Replit app deployed or running in Workspace - Understanding of `.replit` and `replit.nix` - Access to deployment monitoring ## Instructions ### Step 1: Reduce Cold Start Time Autoscale deployments scale to zero when idle. First request triggers a cold start (10-30s). Minimize it: ```typescript // 1. Lazy-load heavy modules — only import when needed // BAD: imports everything at startup import { heavyAnalytics } from './analytics'; // 500ms import { imageProcessor } from './images'; // 300ms // GOOD: import on demand app.get('/api/analyze', async (req, res) => { const { heavyAnalytics } = await import('./analytics'); res.json(await heavyAnalytics.process(req.query)); }); // 2. Defer non-critical initialization let dbPool: Pool | null = null; function getDB(): Pool { if (!dbPool) { dbPool = new Pool({ connectionString: process.env.DATABASE_URL, ssl: { rejectUnauthorized: false }, max: 5, // Keep pool small for faster init }); } return dbPool; } // 3. Start server immediately, initialize after const app = express(); const PORT = parseInt(process.env.PORT || '3000'); app.listen(PORT, '0.0.0.0', () => { console.log(`Server ready in ${process.uptime().toFixed(1)}s`); // Warm up in background after server is accepting requests warmup().catch(console.error); }); async function warmup() { await getDB().query('SELECT 1'); // Pre-connect } ``` ### Step 2: Optimize Nix Environment ```nix # replit.nix — only include what you actually need # BAD: kitchen-sink approach { pkgs }: { deps = [ pkgs.nodejs-20_x pkgs.python311 pkgs.go pkgs.rustc pkgs.cargo pkgs.postgresql pkgs.redis pkgs.imagemagick ]; } # GOOD: minimal deps for a Node.js app { pkgs }: { deps = [ pkgs.nodejs-20_x pkgs.nodePackages.typescript-language-server ]; # Only add postgresql if you need psql CLI: # pkgs.postgresql } ``` ```toml # .replit — pin Nix channel for cache hits [nix] channel = "stable-24_05" # Changing channel invalidates all Nix caches # Only upgrade when needed ``` ### Step 3: Optimize Build Step ```toml # .replit — fast production builds [deployment] build = ["sh", "-c", "npm ci --production && npm run build"] run = ["sh", "-c", "node dist/index.js"] ``` ```json // package.json — optimize build scripts { "scripts": { "build": "tsc --incremental", "start": "node dist/index.js", "dev": "tsx watch src/index.ts" } } ``` ```json // tsconfig.json — incremental builds { "compilerOptions": { "incremental": true, "tsBuildInfoFile": ".tsbuildinfo", "skipLibCheck": true } } ``` Tips for faster builds: - Use `npm ci` (not `npm install`) — deterministic, faster - Add `--production` to skip devDependencies - Use TypeScript `--incremental` for rebuild caching - Avoid `postinstall` scripts that compile native addons ### Step 4: Memory Management Replit containers have memory limits (512 MB to 16 GiB depending on plan/tier): ```typescript // Monitor memory usage function logMemory() { const usage = process.memoryUsage(); const mb = (bytes: number) => Math.round(bytes / 1024 / 1024); console.log({ heapUsed: `${mb(usage.heapUsed)} MB`, heapTotal: `${mb(usage.heapTotal)} MB`, rss: `${mb(usage.rss)} MB`, external: `${mb(usage.external)} MB`, }); } // Check every 60 seconds setInterval(logMemory, 60000); // Expose via health endpoint app.get('/health', (req, res) => { const mem = process.memoryUsage(); res.json({ status: 'ok', uptime: process.uptime(), memoryMB: Math.round(mem.heapUsed / 1024 / 1024), memoryPercent: ((mem.heapUsed / mem.heapTotal) * 100).toFixed(1), }); }); ``` **Memory optimization patterns:** ```typescript // Stream large files instead of loading into memory import { createReadStream } from 'fs'; app.get('/download/:file', (req, res) => { const stream = createReadStream(`/tmp/${req.params.file}`); stream.pipe(res); }); // Paginate database queries app.get('/api/items', async (req, res) => { const page = parseInt(req.query.page as string) || 1; const limit = 50; const offset = (page - 1) * limit; const { rows } = await pool.query( 'SELECT * FROM items ORDER BY id LIMIT $1 OFFSET $2', [limit, offset] ); res.json({ items: rows, page, hasMore: rows.length === limit }); }); // Clear caches when memory is high const cache = new Map(); setInterval(() => { if (process.memoryUsage().heapUsed > 400 * 1024 * 1024) { cache.clear(); console.log('Cache cleared due to high memory'); } }, 30000); ``` ### Step 5: Database Connection Efficiency ```typescript // PostgreSQL pool tuning for Replit const pool = new Pool({ connectionString: process.env.DATABASE_URL, ssl: { rejectUnauthorized: false }, max: 5, // Small pool — containers are limited idleTimeoutMillis: 30000, // Close idle connections after 30s connectionTimeoutMillis: 5000, }); // Use connection pooling, never create per-request connections // BAD: new Pool() per request // GOOD: single pool, shared across requests ``` ### Step 6: Deployment Type Selection | Scenario | Best Type | Why | |----------|-----------|-----| | < 100 daily requests | Autoscale | Free when idle | | Consistent traffic | Reserved VM | No cold starts | | Static frontend | Static | Fastest, cheapest | | Latency-sensitive API | Reserved VM | Always warm | | Cron jobs / webhooks | Reserved VM | Must be always-on | ## Error Handling | Issue | Cause | Solution | |-------|-------|----------| | Cold start > 15s | Heavy imports | Lazy-load, defer init | | OOM killed | Exceeding memory limit | Stream data, reduce pool size | | Build timeout | Slow npm install | Use `npm ci --production` | | Slow first query | DB cold connection | Pre-connect in warmup() | ## Resources - [Replit App Configuration](https://docs.replit.com/replit-app/configuration) - [Nix on Replit](https://docs.replit.com/programming-ide/nix-on-replit) - [Nix Performance](https://blog.replit.com/nix-perf-improvements) - [Reserved VM Deployments](https://docs.replit.com/cloud-services/deployments/reserved-vm-deployments) ## Next Steps For cost optimization, see `replit-cost-tuning`. --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/jeremylongshore) — claim your Tome and manage your conversions.