Why Async and Await Improve Performance in .NET Core

Async and Await Improve Performance (Photo Credit — ChatGPT)

When building high-performance applications with .NET Core, two keywords appear everywhere:

async and await

But a common interview question is:

How exactly do async and await improve performance?

The short answer is that async and await do not necessarily make a single operation faster. Instead, they improve the scalability, responsiveness, and throughput of an application by avoiding blocked threads during I/O-bound operations.

Let’s understand this with a simple example.

The Problem With Synchronous Code

Imagine that we have an API endpoint that retrieves user information from a database.

public IActionResult GetUser(int id)
{
    var user = _dbContext.Users
                 .FirstOrDefault(x => x.Id == id);
    return Ok(user);
}

When this API receives a request, a thread starts executing the code.

When the application sends the query to the database, the thread waits until the database returns the result.

The flow looks like this:

Request arrives
      ↓
Thread starts processing
      ↓
Database query starts
      ↓
Thread waits...
Thread waits…