Question

I have a WCF service deployed to IIS 7 and the client. I thought the service is configured to handle concurrency. When I tested with two client, it took double the amount of time. I have spent hours and not yet able to figure out where I missed it. Any help/suggestions would be appreciated. Service1.svc.cs looks like this:

[ServiceBehavior( ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.PerCall)]
[CallbackBehavior(UseSynchronizationContext=false)]
public class Service1 : IService1
{        
    public byte[] DownloadFile()
    {
        byte[] byt = File.ReadAllBytes(@"C:\Temp\TestFile.pdf");
        System.Threading.Thread.Sleep(1000);
        return byt;
     }
}

Configuration:

    <system.net>
    <connectionManagement>
      <add address="*" maxconnection="100"/>
    </connectionManagement>
  </system.net>
  <system.web>
    <compilation debug="true" targetFramework="4.0" />
    <processModel autoConfig="false" maxWorkerThreads="1400" maxIoThreads="1400" minWorkerThreads="2"/>
    <httpRuntime minFreeThreads="1000" minLocalRequestFreeThreads="1000"/>
  </system.web>
  <system.serviceModel>
    <bindings>
      <basicHttpBinding>
        <binding name="Service1Binding" maxBufferSize="2147483647" maxBufferPoolSize="2147483647"
          maxReceivedMessageSize="2147483647" transferMode="Streamed">
          <readerQuotas maxDepth="2147483647" maxArrayLength="2147483647" maxBytesPerRead="2147483647" />
        </binding>
      </basicHttpBinding>
    </bindings>
    <services>
      <service name="DocService.Service1">        
        <endpoint address="http://localhost/DocService/Service1.svc" binding="basicHttpBinding"
          bindingConfiguration="" name="Service1Binding" bindingName="Service1Binding"
          contract="DocService.IService1" />
        <endpoint address="http://localhost/DocService/mex" binding="mexHttpBinding"
          name="mexpoint" contract="IMetadataExchange" />
      </service>
    </services>    
    <behaviors>
      <serviceBehaviors>
        <behavior>          
          <serviceMetadata httpGetEnabled="true"/>          
          <serviceDebug includeExceptionDetailInFaults="false"/>
          <serviceThrottling maxConcurrentCalls="100" maxConcurrentInstances="100" maxConcurrentSessions="100"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>

Answer 1

The requests are taking much longer than 1s sleep time and the read time of, say, 10mb file. They should complete in maybe 1.1-2s There is something fishy here.

Comment out the read and return a new byte[0]. Does it take 1.0s now? Do you have concurrency now?

Edit: What client are you using?

Edit 2: Responding to your comment, the file transfer is not limiting concurrency in some way. WCF does not care what you do inside your service method. It knows nothing about files. The problem is that your disk is too slow and that serializing 36mb is probably slow too! You server is just too slow! You can find out, if the disk or the serializing is the problem by replacing the IO with new byte[1024*1024*36].