Node.js puรฒ gestire decine di migliaia di connessioni simultanee su un singolo server. Questa guida copre clustering, stream, profiling e strategie di caching.
Capire il ciclo degli eventi
Node.js รจ single-thread. Bloccare il ciclo degli eventi blocca tutte le richieste.
// NEVER do this โ blocks the event loop
app.get('/compute', (req, res) => {
// Synchronous CPU-heavy computation blocks ALL requests
let result = 0;
for (let i = 0; i < 1e9; i++) result += i; // 1 billion iterations!
res.json({ result });
});
// DO THIS instead โ offload to worker thread
const { Worker, isMainThread, parentPort, workerData } = require('worker_threads');
app.get('/compute', (req, res) => {
const worker = new Worker('./computeWorker.js', {
workerData: { input: req.query.n }
});
worker.on('message', result => res.json({ result }));
worker.on('error', err => res.status(500).json({ error: err.message }));
});Clustering per prestazioni multi-core
Node.js viene eseguito su un singolo core CPU per impostazione predefinita.
// Node.js Cluster Module โ Use All CPU Cores
const cluster = require('cluster');
const os = require('os');
const express = require('express');
const NUM_WORKERS = os.cpus().length;
if (cluster.isPrimary) {
console.log(`Primary ${process.pid} is running`);
console.log(`Starting ${NUM_WORKERS} workers...`);
// Fork workers
for (let i = 0; i < NUM_WORKERS; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`Worker ${worker.process.pid} died (${signal || code}). Restarting...`);
cluster.fork(); // Auto-restart crashed workers
});
cluster.on('online', (worker) => {
console.log(`Worker ${worker.process.pid} is online`);
});
} else {
// Worker process โ runs the actual server
const app = express();
app.get('/api/users', async (req, res) => {
const users = await db.getUsers();
res.json(users);
});
app.listen(3000, () => {
console.log(`Worker ${process.pid} listening on port 3000`);
});
}
// Alternative: PM2 cluster mode (recommended for production)
// pm2 start server.js -i max # auto-detect CPU count
// pm2 start server.js -i 4 # explicit countStream per efficienza della memoria
Gli stream permettono di elaborare i dati pezzo per pezzo senza caricare tutto in memoria.
// Node.js Streams โ Memory-Efficient Processing
const fs = require('fs');
const { Transform, pipeline } = require('stream');
const { promisify } = require('util');
const pipelineAsync = promisify(pipeline);
// 1. Stream a large file as HTTP response (no memory buffering)
app.get('/download/large-file', (req, res) => {
const filePath = './large-file.csv';
const stat = fs.statSync(filePath);
res.setHeader('Content-Type', 'text/csv');
res.setHeader('Content-Length', stat.size);
res.setHeader('Content-Disposition', 'attachment; filename=data.csv');
// Pipe file directly to response โ never fully in memory
fs.createReadStream(filePath).pipe(res);
});
// 2. Transform stream for CSV processing
class CsvParser extends Transform {
constructor() {
super({ objectMode: true });
this.buffer = '';
this.headers = null;
}
_transform(chunk, encoding, callback) {
this.buffer += chunk.toString();
const lines = this.buffer.split('\n');
this.buffer = lines.pop(); // Keep incomplete line in buffer
for (const line of lines) {
if (!this.headers) {
this.headers = line.split(',');
continue;
}
const values = line.split(',');
const record = {};
this.headers.forEach((h, i) => record[h.trim()] = values[i]?.trim());
this.push(record);
}
callback();
}
}
// 3. Pipeline for reliable error handling
async function processLargeCsvFile(inputPath, outputPath) {
await pipelineAsync(
fs.createReadStream(inputPath),
new CsvParser(),
new Transform({
objectMode: true,
transform(record, enc, cb) {
// Transform each record
record.processed = true;
cb(null, JSON.stringify(record) + '\n');
}
}),
fs.createWriteStream(outputPath)
);
console.log('Processing complete');
}Strategie di caching
Il caching รจ l'ottimizzazione delle prestazioni con il maggiore impatto.
// Caching Strategies for Node.js
// 1. In-Memory LRU Cache
const { LRUCache } = require('lru-cache');
const cache = new LRUCache({
max: 500, // Maximum 500 items
ttl: 5 * 60 * 1000, // 5 minutes TTL
allowStale: true, // Return stale value while refreshing
updateAgeOnGet: true,
});
async function getUser(id) {
const cacheKey = `user:${id}`;
const cached = cache.get(cacheKey);
if (cached) return cached;
const user = await db.findUser(id);
cache.set(cacheKey, user);
return user;
}
// 2. Redis Cache with Stale-While-Revalidate
const Redis = require('ioredis');
const redis = new Redis();
async function getCachedData(key, fetchFn, ttl = 300) {
const [cached, ttlRemaining] = await redis.pipeline()
.get(key)
.ttl(key)
.exec();
if (cached[1]) {
const data = JSON.parse(cached[1]);
// Background refresh when < 60 seconds remaining
if (ttlRemaining[1] < 60) {
fetchFn().then(fresh =>
redis.setex(key, ttl, JSON.stringify(fresh))
);
}
return data;
}
const data = await fetchFn();
await redis.setex(key, ttl, JSON.stringify(data));
return data;
}
// 3. HTTP Response Caching with ETags
app.get('/api/products', async (req, res) => {
const products = await getProducts();
const etag = require('crypto')
.createHash('md5')
.update(JSON.stringify(products))
.digest('hex');
if (req.headers['if-none-match'] === etag) {
return res.status(304).end();
}
res.setHeader('ETag', etag);
res.setHeader('Cache-Control', 'public, max-age=60, stale-while-revalidate=300');
res.json(products);
});Domande frequenti
Quanti worker del cluster creare?
Crea un worker per core CPU, os.cpus().length worker.
Quando usare gli stream vs caricare in memoria?
Usa gli stream per file superiori a 10 MB, piping di dati e elaborazione incrementale.
Cos'รจ il flag --inspect?
Il flag --inspect avvia Node.js con il protocollo V8 inspector abilitato.
Perchรฉ la mia app Node.js usa cosรฌ tanta memoria?
Cause comuni: perdite di memoria, cache senza eviction, grandi set di dati in memoria.