Simple performance test, C#

Language: Layout:

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace Rextester
{

public class Program
{
	public static void Main(string[] param)
	{
		var rand = new Random();
        List<Entity> a = new List<Entity>();
        List<Entity> b = new List<Entity>();

for (int i = 0; i < 19999; i++)
        {
            a.Add(new Entity() { Id = rand.Next(0, 100) });
            b.Add(new Entity() { Id = rand.Next(0, 100) });
        }

Stopwatch s = new Stopwatch();
        
        s.Start();        
		
        var filteredList = b.Join(a,
                                people => people.Id,
                                person => person.Id,
                                (people, _) => people)
                            .ToList();
        
        s.Stop();
        Console.WriteLine("Method A " + s.ElapsedMilliseconds);
        
        s.Restart();

var hashes = new HashSet<int>(a.Select(e => e.Id));
        var filteredList2 = b.Where(e => hashes.Contains(e.Id)).ToList();
        
        s.Stop();
        Console.WriteLine("Method B " + s.ElapsedMilliseconds);
	}
}

class Entity
{
    public int Id { get; set; }
}
}

Show compiler warnings [ + ] Show input
Compilation time: 0,16 sec, absolute running time: 0,34 sec, cpu time: 0,34 sec, average memory usage: 49 Mb, average nr of threads: 5