c# - Hashset vs List performance

In one of my recent tasks I had to work with text files and extract rows based on certain values contained in a specific column.

I had a 4 GB file and I had to parse that file to extract rows that matched certain keywords.The total keyword matches varied from 10000 to less than a million.

For a smaller set of keywords I have used List but noticed that as the list items grew in size the lookup  operation became slower.Below is a test I did to compare the lookup performance between a List<string> and HashSet<string>

HashSet<string> lookup is faster and should be used for lookup instead of a list.

using System;

using System.Collections.Generic;

using System.Diagnostics;

namespace HashSetListCompare

{

    class Program

    {

        static void Main(string[] args)

        {

            try

            {

                string s = "512367";

                List<string> sNumbersList = new List<string>();

                HashSet<string> sNumbersHashSet = new HashSet<string>();

                //List load performance

                Stopwatch oListLoad = new Stopwatch();

                oListLoad.Start();

                for (int i = 0; i < 1000000; i++)

                    sNumbersList.Add(i.ToString());

                oListLoad.Stop();

                Console.WriteLine("List load time:" + oListLoad.Elapsed);

                //Hash Set load performance

                Stopwatch oHashSetLoad = new Stopwatch();

                oHashSetLoad.Start();

                for (int i = 0; i < 1000000; i++)

                    sNumbersHashSet.Add(i.ToString());

                oHashSetLoad.Stop();

                Console.WriteLine("Hash load time:" + oHashSetLoad.Elapsed);

                //List lookup performance

                Stopwatch oListWatch = new Stopwatch();

                oListWatch.Start();

                if(sNumbersList.Contains(s))

                    Console.Write("List lookup time: ");

                oListWatch.Stop();

                Console.WriteLine(oListWatch.Elapsed);

                //Hash set lookup performance

                Stopwatch oHashSetWatch = new Stopwatch();

                oHashSetWatch.Start();

                if(sNumbersHashSet.Contains(s))

                    Console.Write("Hash lookup time: ");

                oHashSetWatch.Stop();

                Console.WriteLine(oHashSetWatch.Elapsed);

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex.Message);

                Console.WriteLine(ex.StackTrace);

            }

            Console.WriteLine("Done");

            Console.Read();

        }

    }

}