Improving performance of multithreaded HttpWebRequests in .NET

Question

I am trying to measure the throughput of a webservice.

In order to do that, I have written a small tool that continuously sends requests and reads responses from a number of threads.

The contents of the inner loop of each thread looks like this:

public void PerformRequest()
{
  WebRequest webRequest = WebRequest.Create(_uri);

  webRequest.ContentType = "application/ocsp-request";
  webRequest.Method = "POST";
  webRequest.Credentials = _credentials;
  webRequest.ContentLength = _request.Length;
  ((HttpWebRequest)webRequest).KeepAlive = false;

  using (Stream st = webRequest.GetRequestStream())
    st.Write(_request, 0, _request.Length);

  using (HttpWebResponse httpWebResponse = (HttpWebResponse)webRequest.GetResponse())
  using (Stream responseStream = httpWebResponse.GetResponseStream())
  using (BufferedStream bufferedStream = new BufferedStream(responseStream))
  using (BinaryReader reader = new BinaryReader(bufferedStream))
  {
    if (httpWebResponse.StatusCode != HttpStatusCode.OK)
      throw new WebException("Got response status code: " + httpWebResponse.StatusCode);

    byte[] response = reader.ReadBytes((int)httpWebResponse.ContentLength);
    httpWebResponse.Close();
  }      
}

It seems to work okay, except that something seems to be limiting the tool. If I run two instances of the tool with each 40 threads, I get significantly more throughput than one instance with 80 threads.

I found the ServicePointManager.DefaultConnectionLimit property, which I set to 10000 (and it makes no difference if I set it through app.config as suggested by Jader Dias).

Are there any other settings in .NET or on my machine that can influence the performance? (I am running Vista, but I see the same problem on Windows Server 2003).

Perhaps some restrictions on how many connections a single process can make?

Answer 1

You must set the maxconnection parameter at the app.config or web.config file:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.net>
    <connectionManagement>
      <add address="*" maxconnection="80"/>
    </connectionManagement>
  </system.net>
</configuration>

Values up to 100 work very well with Windows XP.

Update: I just found out that the method above is an alternative way to set the System.Net.ServicePointManager.DefaultConnectionLimit