Bun Performance Optimization

Bun is already very fast, but you can further improve performance with the right optimization strategies. This chapter introduces performance tuning tips for Bun.

Why Bun is Fast

Architecture Advantages

┌─────────────────────────────────────────┐
│              Bun Architecture            │
├─────────────────────────────────────────┤
│  Core written in Zig language           │
│  JavaScriptCore engine                  │
│  Optimized system calls                 │
│  Built-in features reduce dependencies  │
└─────────────────────────────────────────┘

Performance Comparison

Operation	Node.js	Bun	Improvement
Startup time	40ms	4ms	10x
Package install	30s	1s	30x
HTTP requests/sec	50k	150k	3x
File read	baseline	3x faster	3x

HTTP Server Optimization

Basic Optimization

const server = Bun.serve({
  port: 3000,
  
  // Use concise responses
  fetch(request) {
    // ✅ Return Response directly
    return new Response("Hello!");
    
    // ❌ Avoid unnecessary async
    // return Promise.resolve(new Response("Hello!"));
  },
});

Static Response Caching

// Pre-create common responses
const notFoundResponse = new Response("Not Found", { status: 404 });
const okResponse = new Response("OK");
const jsonHeaders = { "Content-Type": "application/json" };

const server = Bun.serve({
  port: 3000,
  
  fetch(request) {
    const url = new URL(request.url);
    
    if (url.pathname === "/health") {
      return okResponse; // Reuse response object
    }
    
    if (url.pathname === "/api/data") {
      // Pre-computed JSON
      return new Response(cachedJsonString, { headers: jsonHeaders });
    }
    
    return notFoundResponse;
  },
});

Streaming Responses

// Use streaming responses for large data
const server = Bun.serve({
  port: 3000,
  
  fetch(request) {
    const stream = new ReadableStream({
      async start(controller) {
        for (let i = 0; i < 1000; i++) {
          controller.enqueue(`data: ${i}\n`);
          // Don't block other requests
          if (i % 100 === 0) {
            await Bun.sleep(0);
          }
        }
        controller.close();
      },
    });
    
    return new Response(stream, {
      headers: { "Content-Type": "text/event-stream" },
    });
  },
});

File I/O Optimization

Using Bun.file()

// ✅ Use Bun.file (fastest)
const content = await Bun.file("./data.txt").text();

// ❌ Avoid Node.js fs (slower)
// import { readFile } from "fs/promises";
// const content = await readFile("./data.txt", "utf-8");

Batch File Operations

// ✅ Read multiple files in parallel
const files = ["a.txt", "b.txt", "c.txt"];
const contents = await Promise.all(
  files.map(f => Bun.file(f).text())
);

// ❌ Avoid serial reads
// for (const f of files) {
//   contents.push(await Bun.file(f).text());
// }

Streaming Writes for Large Files

// Use writer for large files
const writer = Bun.file("./large-output.txt").writer();

for (let i = 0; i < 1000000; i++) {
  writer.write(`Line ${i}\n`);
  
  // Periodically flush buffer
  if (i % 10000 === 0) {
    await writer.flush();
  }
}

await writer.end();

Database Optimization

SQLite Optimization

import { Database } from "bun:sqlite";

const db = new Database("app.db");

// Enable WAL mode
db.run("PRAGMA journal_mode = WAL");
db.run("PRAGMA synchronous = NORMAL");
db.run("PRAGMA cache_size = -64000"); // 64MB cache
db.run("PRAGMA temp_store = MEMORY");

// Use prepared statements
const insert = db.prepare("INSERT INTO items (name) VALUES (?)");
const select = db.prepare("SELECT * FROM items WHERE id = ?");

// Batch inserts using transactions
const insertMany = db.transaction((items: string[]) => {
  for (const item of items) {
    insert.run(item);
  }
});

Connection Pool Pattern

// Create multiple connections for high concurrency scenarios
class DatabasePool {
  private connections: Database[] = [];
  private index = 0;
  
  constructor(path: string, size: number = 4) {
    for (let i = 0; i < size; i++) {
      const db = new Database(path);
      db.run("PRAGMA journal_mode = WAL");
      this.connections.push(db);
    }
  }
  
  get(): Database {
    this.index = (this.index + 1) % this.connections.length;
    return this.connections[this.index];
  }
  
  close() {
    for (const conn of this.connections) {
      conn.close();
    }
  }
}

Memory Optimization

Reducing Memory Allocation

// ✅ Reuse Buffer
const buffer = new Uint8Array(1024);

function processData(data: Uint8Array) {
  // Use pre-allocated buffer
  buffer.set(data.slice(0, 1024));
  return processBuffer(buffer);
}

// ❌ Avoid creating new objects frequently
// function processData(data) {
//   const buffer = new Uint8Array(1024); // Allocated each time
//   ...
// }

Using --smol Mode

# Reduce memory usage (suitable for constrained environments)
bun --smol app.ts

Monitoring Memory Usage

// Periodically check memory
setInterval(() => {
  const usage = process.memoryUsage();
  console.log({
    heapUsed: `${(usage.heapUsed / 1024 / 1024).toFixed(2)} MB`,
    heapTotal: `${(usage.heapTotal / 1024 / 1024).toFixed(2)} MB`,
    external: `${(usage.external / 1024 / 1024).toFixed(2)} MB`,
  });
}, 10000);

Concurrency Optimization

Using Workers

// main.ts
const worker = new Worker("./worker.ts");

worker.postMessage({ type: "process", data: [1, 2, 3, 4, 5] });

worker.onmessage = (event) => {
  console.log("Result:", event.data);
};

// worker.ts
self.onmessage = (event) => {
  const { type, data } = event.data;
  
  if (type === "process") {
    const result = data.map((n: number) => n * 2);
    self.postMessage(result);
  }
};

Parallel Processing

// Use Promise.all for parallel processing
async function processItems(items: string[]) {
  const batchSize = 100;
  const batches = [];
  
  for (let i = 0; i < items.length; i += batchSize) {
    batches.push(items.slice(i, i + batchSize));
  }
  
  const results = await Promise.all(
    batches.map(batch => processBatch(batch))
  );
  
  return results.flat();
}

Build Optimization

Production Build

await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  
  // Production optimization
  minify: true,
  
  // Tree Shaking
  treeshaking: true,
  
  // Define environment
  define: {
    "process.env.NODE_ENV": JSON.stringify("production"),
  },
});

Code Splitting

await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  splitting: true, // Automatic code splitting
});

Network Optimization

Connection Reuse

// Reuse HTTP connections
const agent = {
  keepAlive: true,
  keepAliveMsecs: 30000,
};

// Bun reuses connections by default, but can be configured

Compressing Responses

const server = Bun.serve({
  port: 3000,
  
  async fetch(request) {
    const data = JSON.stringify(largeData);
    
    // Check if client supports compression
    const acceptEncoding = request.headers.get("accept-encoding") || "";
    
    if (acceptEncoding.includes("gzip")) {
      const compressed = Bun.gzipSync(data);
      return new Response(compressed, {
        headers: {
          "Content-Type": "application/json",
          "Content-Encoding": "gzip",
        },
      });
    }
    
    return Response.json(largeData);
  },
});

Performance Analysis

Built-in Profiling

# View detailed startup time
bun --timing app.ts

Custom Timing

// Use console.time
console.time("operation");
await heavyOperation();
console.timeEnd("operation");

// Or use performance
const start = performance.now();
await heavyOperation();
const duration = performance.now() - start;
console.log(`Duration: ${duration.toFixed(2)}ms`);

Benchmark Testing

// bench.ts
import { bench, run } from "bun:test";

bench("string concatenation", () => {
  let s = "";
  for (let i = 0; i < 1000; i++) {
    s += "x";
  }
});

bench("array join", () => {
  const arr = [];
  for (let i = 0; i < 1000; i++) {
    arr.push("x");
  }
  arr.join("");
});

await run();

Run:

bun run bench.ts

Best Practices Checklist

✅ Recommended Practices

1. Use Bun Native APIs

   • Bun.file() instead of fs
   • Bun.serve() instead of http
   • bun:sqlite instead of third-party libraries

2. Reduce Allocations

   • Reuse objects and buffers
   • Use object pools
   • Avoid unnecessary copies

3. Batch Processing

   • Use transactions for database operations
   • Batch file operations
   • Reduce I/O counts

4. Parallel Processing

   • Promise.all for parallel requests
   • Workers for CPU-intensive tasks
   • Streaming for large data

5. Proper Configuration

   • Enable compression
   • Use WAL mode
   • Configure cache

❌ Practices to Avoid

1. Frequently creating new objects
2. Synchronous blocking operations
3. Ignoring connection reuse
4. Unoptimized database queries
5. Unnecessary data copying

Summary

This chapter introduced:

• ✅ Bun's performance advantages
• ✅ HTTP server optimization
• ✅ File and database optimization
• ✅ Memory and concurrency optimization
• ✅ Build and network optimization
• ✅ Performance analysis tools
• ✅ Best practices checklist

Next Steps

Continue reading Node.js Compatibility to learn how to migrate from Node.js to Bun.