Why does file extension affect write speed? (C#, StreamWriter)

Question

I am currently testing the performance of different methods for logging text data into a file. It seems that when I open/write/close a large amount of times, the extension used affects the performance. (.txt and .log are ~7 times faster)

Code used:

private static void TestWriteSpeed(FileInfo file)
{
    Stopwatch watch = new Stopwatch();
    watch.Start();
    for (int i = 0; i < 5000; i++)
    {
        using (StreamWriter writer = file.AppendText())
        {
            writer.Write("This is a test");
        }
    }
    Console.WriteLine(file.Name + ": " + watch.Elapsed);
}

static void Main(string[] args)
{
    TestWriteSpeed(new FileInfo("abc.txt"));
    TestWriteSpeed(new FileInfo("abc.txt.01564611564"));
    TestWriteSpeed(new FileInfo("abc.01564611564.txt"));
    TestWriteSpeed(new FileInfo("abc.xml"));
    TestWriteSpeed(new FileInfo("abc.xml.01564611564"));
    TestWriteSpeed(new FileInfo("abc.config"));
    TestWriteSpeed(new FileInfo("abc.config.01564611564"));
    TestWriteSpeed(new FileInfo("abc.exe"));
    TestWriteSpeed(new FileInfo("abc.exe.01564611564"));
    TestWriteSpeed(new FileInfo("abc.log"));
    TestWriteSpeed(new FileInfo("abc.log.01564611564"));
    Console.ReadLine();
}

Results:

abc.txt                  00:00:08.3826847  <---
abc.txt.01564611564      00:00:59.7401633
abc.01564611564.txt      00:00:08.0069698  <---
abc.xml                  00:00:58.2031820
abc.xml.01564611564      00:00:59.3956204
abc.config               00:00:58.4861308
abc.config.01564611564   00:01:01.2474287
abc.exe:                 00:01:00.0924401
abc.exe.01564611564      00:01:00.7371805
abc.log                  00:00:08.0009934  <---
abc.log.01564611564      00:00:59.8029448

Why is this happening?

Answer 1

As Orsol suggested, your AV may be ignoring txt and log files.

Answer 2

Looks like another application or process is reading or monitoring the files being written and ignoring .txt or .log files for performance reason.

Why ? Because your bunch of code, when run on my laptop, give same results for all the files (22 seconds), without any variations.

Answer 3

I tested this on my work machine; a Core 2 machine with 32-bit Windows XP with Symantec Endpoint Protection AV installed. These are my results:

abc.txt:                00:00:07.1192029  
abc.txt.01564611564:    00:00:06.9956377  
abc.01564611564.txt:    00:00:06.9534773  
abc.xml:                00:00:06.9368894  
abc.xml.01564611564:    00:00:07.9326258  
abc.config:             00:00:07.9074675  
abc.config.01564611564: 00:00:08.0205423  
abc.exe:                00:00:21.2559372  
abc.exe.01564611564:    00:00:07.2417322  
abc.log:                00:00:07.0871043  
abc.log.01564611564:    00:00:07.1848522

In my case, it was only the .exe extension that took longer.

So yes, at a guess, the anti-virus is interfering with write speeds.

Edit: I should note, this user is a Limited User on an AD domain.