Performance Showdown

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var cursors = new List<Cursor>();
            cursors.Add(new Cursor
            {
                EscapedKey = "MyHub",
                Id = 0
            });

            cursors.Add(new Cursor
            {
                EscapedKey = "MyHub2",
                Id = 1
            });

            cursors.Add(new Cursor
            {
                EscapedKey = "MyHub.Group",
                Id = 0
            });

            int iterations = 1000000;

            var sw = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                MakeCursorJoin(cursors);
            }
            sw.Stop();

            Console.WriteLine("Concat {0}", sw.Elapsed);

            sw = Stopwatch.StartNew();
            for (int i = 0; i < iterations; i++)
            {
                MakeCursorStringBuilder(cursors);
            }
            sw.Stop();
            Console.WriteLine("StringBuilder {0}", sw.Elapsed);

        }

        private static string MakeCursorJoin(IList<Cursor> cursors)
        {
            var serialized = new string[cursors.Count];
            for (int i = 0; i < cursors.Count; i++)
            {
                serialized[i] = cursors[i].EscapedKey + ',' + cursors[i].Id;
            }

            return String.Join("|", serialized);
        }

        private static string MakeCursorStringBuilder(IList<Cursor> cursors)
        {
            var sb = new StringBuilder();
            for (int i = 0; i < cursors.Count; i++)
            {
                if (i > 0)
                {
                    sb.Append('|');
                }

                sb.Append(cursors[i].EscapedKey)
                  .Append(',')
                  .Append(cursors[i].Id);
            }

            return sb.ToString();
        }
    }

    public class Cursor
    {
        public string EscapedKey { get; set; }
        public ulong Id { get; set; }
    }
}

Results

Concat: 00:00:00.8572315
StringBuilder: 00:00:00.7025375

Memory (I ran these by commenting out each and running the CLR profiler) for each method:
Concat:

StringBuilder:

A quick test to share what I'm seeing (differently). Code was executed using LINQPad 4.42.05 beta (anyCPU) and LINQPad 4.42.01 (x86), respectively, and optimizations were turned on.

Results (x64)

Concat 00:00:00.5541643
StringBuilder 00:00:00.4194049

Results (x86)

Concat 00:00:00.4938912
StringBuilder 00:00:00.4087391

Test Configuration

• OS Name: Microsoft Windows 7 Enterprise
• Version: 6.1.7601 Service Pack 1 Build 7601
• System Type: x64-based PC
• Processor: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz, 3401 Mhz, 4 Core(s), 8 Logical Processor(s)
• Installed Physical Memory (RAM): 8.00 GB