Introduction

When it comes to processing strings in C#, splitting a string into parts is a common task. Whether you’re parsing CSV files, extracting tokens from a sentence, or simply working with substrings, knowing how to efficiently split strings is crucial for performance-sensitive applications. In this article, we will explore the performance differences between two common string-splitting techniques in C#: String.Split() and ReadOnlySpan.Split(). Through benchmarking, we will demonstrate that using ReadOnlySpan.Split() offers significant performance advantages, especially in scenarios that require splitting large strings or processing strings repeatedly.

The Problem with String.Split()

The String.Split() method in C# is straightforward and easy to use, but it comes with some performance overhead. Every time you split a string, it internally allocates a new array to hold the resulting substrings. This allocation leads to increased memory usage, and if the method is called frequently or in a memory-sensitive application, it can contribute to unnecessary garbage collection (GC) overhead. Specifically, String.Split() uses heap allocations, which can result in more frequent garbage collection cycles in the Gen 0 and Gen 1 generations.

The Advantage of ReadOnlySpan.Split()

On the other hand, the ReadOnlySpan.Split() method, which works with ReadOnlySpan<T> (a type introduced in .NET Core), offers a different approach. Instead of allocating new strings, it works directly on the data in the original string without copying it. This reduces memory usage and avoids unnecessary allocations, leading to fewer garbage collections. The ReadOnlySpan type provides a lightweight, stack-only representation of data that enables high-performance operations on string data. It’s particularly useful in high-throughput applications where performance is critical.

Benchmarking String.Split() vs ReadOnlySpan.Split()

To evaluate the performance difference between the two methods, we can use a benchmarking library like BenchmarkDotNet. This tool allows us to precisely measure the execution time and memory usage of different methods, so we can make an informed decision on which method to use in our code.

Here is how we can set up the benchmark:

In the example above, we define a benchmark for both String.Split() and ReadOnlySpan.Split(). The SplitWithReadOnlySpan() method calls AsSpan() on the string, which creates a ReadOnlySpan<char>, and then calls the Split() method on that span.

To execute the benchmark, you can use the following command:

This will compile the project in release mode and run the benchmark. The output will show the performance results for each method.

Performance Results

As demonstrated in the benchmark results (Figure 2), ReadOnlySpan.Split() performs significantly better than String.Split(). The key differences include:

• Fewer Allocations: ReadOnlySpan.Split() eliminates the need for allocating new arrays for each substring, reducing memory usage.
• Lower GC Pressure: Since ReadOnlySpan operates on stack-allocated memory, it reduces the frequency of garbage collection, especially in Gen 0 and Gen 1.
• Improved Throughput: With fewer allocations and less GC overhead, ReadOnlySpan.Split() executes faster, especially for larger strings or more complex splitting tasks.

When to Use ReadOnlySpan.Split()

While String.Split() is suitable for many common use cases, the ReadOnlySpan.Split() method should be preferred when:

1. Memory Efficiency: You are working with large strings or processing many strings in quick succession and want to reduce memory allocation.
2. Performance Sensitivity: You need to minimize the impact of garbage collection and maximize throughput.
3. No Need for String Mutability: Since ReadOnlySpan works directly on the original string without creating copies, it is ideal when you do not need to mutate the resulting substrings.

Conclusion

In conclusion, when working with string splitting operations in C#, it’s important to consider the performance implications of your choice of method. Although String.Split() is easy to use and sufficient for many scenarios, it introduces unnecessary memory allocations and garbage collection overheads. On the other hand, ReadOnlySpan.Split() offers a more efficient, allocation-free alternative that improves performance in high-throughput applications. If your application requires high-performance string processing, leveraging ReadOnlySpan.Split() is a great choice.