This small example should show the performance comparison between List and HashSet
Docs:
BenchmarkDotNet v0.13.9+228a464e8be6c580ad9408e98f18813f6407fb5a, Windows 10 (10.0.19045.3570/22H2/2022Update)
AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 8.0.100-rc.2.23502.2
[Host] : .NET 7.0.13 (7.0.1323.51816), X64 RyuJIT AVX2
.NET 7.0 : .NET 7.0.13 (7.0.1323.51816), X64 RyuJIT AVX2
.NET 8.0 : .NET 8.0.0 (8.0.23.47906), X64 RyuJIT AVX2
| Method | Runtime | Count | Mean | Error | StdDev | Gen0 | Gen1 | Allocated |
|------------- |--------- |------ |------------:|----------:|----------:|-------:|-------:|----------:|
| ListWrite | .NET 7.0 | 10 | 29.24 ns | 0.512 ns | 0.479 ns | 0.0057 | - | 96 B |
| ListWrite | .NET 8.0 | 10 | 17.70 ns | 0.372 ns | 0.348 ns | 0.0057 | - | 96 B |
| | | | | | | | | |
| HashSetWrite | .NET 7.0 | 10 | 77.12 ns | 1.555 ns | 2.804 ns | 0.0176 | - | 296 B |
| HashSetWrite | .NET 8.0 | 10 | 68.13 ns | 1.347 ns | 1.843 ns | 0.0176 | - | 296 B |
| | | | | | | | | |
| ListDistinct | .NET 7.0 | 10 | 199.39 ns | 3.804 ns | 3.736 ns | 0.0353 | - | 592 B |
| ListDistinct | .NET 8.0 | 10 | 179.22 ns | 3.521 ns | 3.458 ns | 0.0353 | - | 592 B |
| | | | | | | | | |
| ListWrite | .NET 7.0 | 100 | 205.82 ns | 3.058 ns | 2.711 ns | 0.0272 | - | 456 B |
| ListWrite | .NET 8.0 | 100 | 96.70 ns | 1.599 ns | 1.496 ns | 0.0272 | - | 456 B |
| | | | | | | | | |
| HashSetWrite | .NET 7.0 | 100 | 642.95 ns | 5.789 ns | 5.132 ns | 0.1087 | - | 1832 B |
| HashSetWrite | .NET 8.0 | 100 | 526.90 ns | 6.265 ns | 5.861 ns | 0.1087 | - | 1832 B |
| | | | | | | | | |
| ListDistinct | .NET 7.0 | 100 | 1,466.94 ns | 27.696 ns | 25.907 ns | 0.1698 | - | 2848 B |
| ListDistinct | .NET 8.0 | 100 | 1,026.49 ns | 11.527 ns | 10.782 ns | 0.1698 | - | 2848 B |
| | | | | | | | | |
| ListWrite | .NET 7.0 | 500 | 967.23 ns | 15.021 ns | 14.051 ns | 0.1221 | - | 2056 B |
| ListWrite | .NET 8.0 | 500 | 440.48 ns | 6.749 ns | 6.313 ns | 0.1225 | - | 2056 B |
| | | | | | | | | |
| HashSetWrite | .NET 7.0 | 500 | 2,831.40 ns | 23.379 ns | 19.522 ns | 0.5035 | - | 8456 B |
| HashSetWrite | .NET 8.0 | 500 | 2,434.14 ns | 37.114 ns | 41.252 ns | 0.5035 | - | 8456 B |
| | | | | | | | | |
| ListDistinct | .NET 7.0 | 500 | 6,531.18 ns | 64.563 ns | 57.233 ns | 0.7553 | 0.0153 | 12672 B |
| ListDistinct | .NET 8.0 | 500 | 4,712.75 ns | 62.142 ns | 51.891 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.
- 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- 2023/11 - Add .NET 8