How do I improve the performance of code using DateTime.ToString?

Question

In my binary to text decoding application (.NET 2.0) I found that the line:

logEntryTime.ToString("dd.MM.yy HH:mm:ss:fff") 

takes 33% of total processing time. Does anyone have any ideas on how to make it faster?

EDIT: This app is used to process some binary logs and it currently takes 15 hours to run. So 1/3 of this will be 5 hours.

EDIT: I am using NProf for profiling. App is processing around 17 GBytes of binary logs.

Answer 1

It's unfortunate that .NET doesn't have a sort of "formatter" type which can parse a pattern and remember it.

If you're always using the same format, you might want to hand-craft a formatter to do exactly that. Something along the lines of:

public static string FormatDateTime(DateTime dt) {     char[] chars = new char[21];     Write2Chars(chars, 0, dt.Day);     chars[2] = '.';     Write2Chars(chars, 3, dt.Month);     chars[5] = '.';     Write2Chars(chars, 6, dt.Year % 100);     chars[8] = ' ';     Write2Chars(chars, 9, dt.Hour);     chars[11] = ' ';     Write2Chars(chars, 12, dt.Minute);     chars[14] = ' ';     Write2Chars(chars, 15, dt.Second);     chars[17] = ' ';     Write2Chars(chars, 18, dt.Millisecond / 10);     chars[20] = Digit(dt.Millisecond % 10);      return new string(chars); }  private static void Write2Chars(char[] chars, int offset, int value) {     chars[offset] = Digit(value / 10);     chars[offset+1] = Digit(value % 10); }  private static char Digit(int value) {     return (char) (value + '0'); } 

This is pretty ugly, but it's probably a lot more efficient... benchmark it, of course!

Answer 2

Are you sure it takes 33% of the time? How have you measured that? It sounds more than a little suspicious to me...

This makes things a little bit quicker:

Basic: 2342ms Custom: 1319ms 

Or if we cut out the IO (Stream.Null):

Basic: 2275ms Custom: 839ms 

---

using System.Diagnostics; using System; using System.IO; static class Program {     static void Main()     {         DateTime when = DateTime.Now;         const int LOOP = 1000000;          Stopwatch basic = Stopwatch.StartNew();         using (TextWriter tw = new StreamWriter("basic.txt"))         {             for (int i = 0; i < LOOP; i++)             {                 tw.Write(when.ToString("dd.MM.yy HH:mm:ss:fff"));             }         }         basic.Stop();         Console.WriteLine("Basic: " + basic.ElapsedMilliseconds + "ms");          char[] buffer = new char[100];         Stopwatch custom = Stopwatch.StartNew();         using (TextWriter tw = new StreamWriter("custom.txt"))         {             for (int i = 0; i < LOOP; i++)             {                 WriteDateTime(tw, when, buffer);             }         }         custom.Stop();         Console.WriteLine("Custom: " + custom.ElapsedMilliseconds + "ms");     }     static void WriteDateTime(TextWriter output, DateTime when, char[] buffer)     {         buffer[2] = buffer[5] = '.';         buffer[8] = ' ';         buffer[11] = buffer[14] = buffer[17] = ':';         Write2(buffer, when.Day, 0);         Write2(buffer, when.Month, 3);         Write2(buffer, when.Year % 100, 6);         Write2(buffer, when.Hour, 9);         Write2(buffer, when.Minute, 12);         Write2(buffer, when.Second, 15);         Write3(buffer, when.Millisecond, 18);         output.Write(buffer, 0, 21);     }     static void Write2(char[] buffer, int value, int offset)     {         buffer[offset++] = (char)('0' + (value / 10));         buffer[offset] = (char)('0' + (value % 10));     }     static void Write3(char[] buffer, int value, int offset)     {         buffer[offset++] = (char)('0' + (value / 100));         buffer[offset++] = (char)('0' + ((value / 10) % 10));         buffer[offset] = (char)('0' + (value % 10));     } }