The efficient way to measure time in .NET

One of my new year resolution for 2025 is to share my coding and engineering challenges, learnings and musings.

Today, i'll like to share a technique that i recently discovered whilst trying to measure how long it takes to execute a method or function in .NET. I faced this challenge when working with the vector search component of Weaviate. Weaviate is open-source vector database state-of-the-art machine learning (ML) models to turn your data - text, images, and more - into a searchable vector database. It stores both objects and vectors, allowing for the combination of vector search with structured filtering. Thus, the performance of search is integral especially for a database.

Now, there are many ways to measure time in .NET. The common way these days is using Stopwatch class like this:

Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
// Your code: Doing something e.g Thread.Sleep(3000);
stopwatch.Stop();
TimeSpan elapsedTime = stopwatch.Elapsed;

However, i found the Stopwatch object creation and memory allocation time consuming in our app. I tried to factor the memory/time used by Stopwatch but it became an issue when you have more than one stopwatch. And in the vector search algorithm, every seconds counts. So my search for alternatives led me to this
this performant and modern way introduced in .NET 7.

This is how it's done

long startTime = Stopwatch.GetTimestamp();
// Your code: Doing something e.g Thread.Sleep(3000);
TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);


With this new approach:

• you are dont need to create a new Stopwatch instance hence no memory allocations on the heap, making it ideal for performance-critical paths.

• The underlying timestamp for the Stopwatch methods is monotonic i.e. they are not affected by time changing due to Network Time Protocol (NTP) time sync changes or other sources of system time change.

• The code is also simple and clear about its intent. I often see people forget to stop the StopWatch in the previous style. This new style is clean.
  Nick Chapsas gave a nice video talk about this as well

As i mentioned earlier, there are other ways to measure how long it takes to execute a method or function in .NET

1. Through Professional tools like
   Visual studio Performance tool
   BenchmarkDotNet
   DotTrace Profiler by Rider, Dynatrace
   Datadog

2. DateTime and TimeSpan
   Using DateTime, you can register the time before and after the execution of the code that you want to measure and

DateTime start = DateTime.UtcNow;
// Your code: Doing something e.g Thread.Sleep(3000);
DateTime end = DateTime.UtcNow;
TimeSpan timeDiff = end - start;
Console.WriteLine(Convert.ToInt32(timeDiff.TotalMilliseconds));

I wont recommend using the DateTime approach because it is not monotonic and relies on a lot of other variables as described in Nick Chapsas video

Thanks for reading. Hope you find this useful