This small example should show the performance comparison between List and HashSet
Docs:
BenchmarkDotNet v0.14.0, Windows 10 (10.0.19045.5131/22H2/2022Update)
AMD Ryzen 9 9950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 9.0.100
[Host] : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
.NET 7.0 : .NET 7.0.20 (7.0.2024.26716), X64 RyuJIT AVX2
.NET 8.0 : .NET 8.0.11 (8.0.1124.51707), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
.NET 9.0 : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
| Method | Runtime | Count | Mean | Gen0 | Gen1 | Allocated |
|------------- |--------- |------ |------------:|-------:|-------:|----------:|
| ListWrite | .NET 7.0 | 10 | 17.62 ns | 0.0057 | - | 96 B |
| ListWrite | .NET 8.0 | 10 | 10.36 ns | 0.0057 | - | 96 B |
| ListWrite | .NET 9.0 | 10 | 10.14 ns | 0.0057 | - | 96 B |
| | | | | | | |
| HashSetWrite | .NET 7.0 | 10 | 46.45 ns | 0.0176 | - | 296 B |
| HashSetWrite | .NET 8.0 | 10 | 38.23 ns | 0.0176 | - | 296 B |
| HashSetWrite | .NET 9.0 | 10 | 36.40 ns | 0.0176 | - | 296 B |
| | | | | | | |
| ListDistinct | .NET 7.0 | 10 | 117.86 ns | 0.0353 | - | 592 B |
| ListDistinct | .NET 8.0 | 10 | 92.83 ns | 0.0353 | - | 592 B |
| ListDistinct | .NET 9.0 | 10 | 72.39 ns | 0.0353 | - | 592 B |
| | | | | | | |
| ListWrite | .NET 7.0 | 100 | 161.84 ns | 0.0272 | - | 456 B |
| ListWrite | .NET 8.0 | 100 | 66.02 ns | 0.0272 | - | 456 B |
| ListWrite | .NET 9.0 | 100 | 70.78 ns | 0.0272 | - | 456 B |
| | | | | | | |
| HashSetWrite | .NET 7.0 | 100 | 392.54 ns | 0.1092 | - | 1832 B |
| HashSetWrite | .NET 8.0 | 100 | 310.50 ns | 0.1092 | - | 1832 B |
| HashSetWrite | .NET 9.0 | 100 | 302.29 ns | 0.1092 | - | 1832 B |
| | | | | | | |
| ListDistinct | .NET 7.0 | 100 | 958.11 ns | 0.1698 | 0.0010 | 2848 B |
| ListDistinct | .NET 8.0 | 100 | 654.36 ns | 0.1698 | 0.0010 | 2848 B |
| ListDistinct | .NET 9.0 | 100 | 485.05 ns | 0.1698 | 0.0010 | 2848 B |
| | | | | | | |
| ListWrite | .NET 7.0 | 500 | 796.96 ns | 0.1221 | - | 2056 B |
| ListWrite | .NET 8.0 | 500 | 316.34 ns | 0.1225 | - | 2056 B |
| ListWrite | .NET 9.0 | 500 | 233.99 ns | 0.1228 | - | 2056 B |
| | | | | | | |
| HashSetWrite | .NET 7.0 | 500 | 1,861.07 ns | 0.5054 | - | 8456 B |
| HashSetWrite | .NET 8.0 | 500 | 1,441.61 ns | 0.5054 | - | 8456 B |
| HashSetWrite | .NET 9.0 | 500 | 1,464.85 ns | 0.5054 | - | 8456 B |
| | | | | | | |
| ListDistinct | .NET 7.0 | 500 | 4,421.42 ns | 0.7553 | 0.0153 | 12672 B |
| ListDistinct | .NET 8.0 | 500 | 2,955.31 ns | 0.7553 | 0.0153 | 12672 B |
| ListDistinct | .NET 9.0 | 500 | 2,269.79 ns | 0.7553 | 0.0153 | 12672 B |- 🚀 HashSet is a collection that ensures that each element exists only once and thus no manual distinct has to be made. However, this is bought by a performance loss and allocations when inserting the elements!
- The performance benefits of .NET 8 are almost twice as high as in .NET 7.
- Performance has been improved even further with .NET 9.
- The more elements to write, the higher the performance loss
- It must be considered how relevant a distinct is and which quantity should be compared
- Use the HashSet only if you really need to ensure that each element exists only once
dotnet run -c Release --framework net9.0- 2023/11 - Add .NET 8
- 2024/11 - Add .NET 9