In the world of Node.js, async/await has become a staple for handling asynchronous operations. It’s clean, easy to read, and feels synchronous. But as wonderful as it sounds, misusing async/await can introduce performance bottlenecks that slow down your application.

If your app feels sluggish despite using async/await, this post is for you.

Why Async/Await Feels Slow

Under the hood, async/await doesn’t do magic — it wraps your asynchronous operations in promises. When used improperly, async/await can introduce unnecessary blocking and sequential execution, which undermines the non-blocking, asynchronous nature of Node.js.

Here are common scenarios where async/await could slow your app:

1. Sequential Execution Instead of Parallel Execution

Async/await runs functions one at a time unless you explicitly handle them in parallel. Take this example:

async function fetchUserData() {
  const user = await getUser(); // First request
  const orders = await getOrders(user.id); // Second request
  const profile = await getUserProfile(user.id); // Third request

  return { user, orders, profile };
}

Here, the getUser, getOrders, and getUserProfile calls are executed sequentially. Each one waits for the previous one to complete, increasing overall execution time.

Fix: Run Async Functions in Parallel Using Promise.all

To avoid sequential execution, we can run these promises in parallel:

async function fetchUserData() {
  const [user, orders, profile] = await Promise.all([
    getUser(),
    getOrders(userId),
    getUserProfile(userId),
  ]);

  return { user, orders, profile };
}

With Promise.all, all three operations are executed concurrently, drastically reducing execution time.

2. N+1 Query Problem

This is common when fetching data in loops:

async function fetchOrderDetails(orders) {
  const details = [];
  
  for (const order of orders) {
    const detail = await getOrderDetail(order.id); // Awaits one at a time
    details.push(detail);
  }

  return details;
}

Here, each getOrderDetail call waits for the previous one to finish. If you’re looping through hundreds of orders, this approach can be painfully slow.

Fix: Use Promise.all in Loops

Instead of waiting sequentially, fire all promises simultaneously:

async function fetchOrderDetails(orders) {
  const details = await Promise.all(
    orders.map(order => getOrderDetail(order.id))
  );

  return details;
}

This runs the promises concurrently, massively improving performance.

3. Blocking Long-Tail Operations

If you mix long-running async operations with critical code, the blocking nature of async/await can delay important tasks:

async function processRequest(req) {
  const user = await getUser(req.userId); // Necessary
  const analytics = await updateAnalytics(req); // Non-critical but blocks user fetch

  return { user, status: 'Processed' };
}

The second operation (updateAnalytics) slows down the overall response, even though it’s non-critical.

Fix: Handle Non-Critical Tasks Separately

Move non-critical operations out of the main flow:

async function processRequest(req) {
  const user = await getUser(req.userId);

  // Update analytics separately (fire-and-forget)
  updateAnalytics(req).catch(err => console.error('Analytics Error:', err));

  return { user, status: 'Processed' };
}

Now, updateAnalytics runs in the background without impacting response time.

Best Practices to Avoid Async/Await Pitfalls

• Batch Your Promises
• Use Promise.all to group promises that can run concurrently.
• Limit Concurrency
• If dealing with a large number of parallel requests, use libraries like p-limit to control concurrency.

const pLimit = require('p-limit');
const limit = pLimit(5); // Limit to 5 concurrent requests

const results = await Promise.all(
  tasks.map(task => limit(() => asyncTask(task)))
);

• Avoid Mixing Sync and Async Code
• Keep your async workflows separate and well-optimized. Avoid wrapping already synchronous code in async/await.
• Lazy Load Expensive Calls
• Don’t call expensive APIs unnecessarily. Use conditional logic to call them only when needed.

const profile = condition ? await fetchProfile(user.id) : null;

• Use Tools for Debugging
• Tools like Clinic.js and built-in Node.js profilers can help identify async bottlenecks.

Final Thoughts

Async/await is a fantastic tool for readability and maintainability, but it’s easy to misuse.

Remember, Node.js thrives on non-blocking concurrency. Use async/await wisely, and don’t forget to leverage parallelism (Promise.all) when appropriate.