Why is the first WCF client call slow?

问题

I am trying to figure out why the first WCF call after client application start takes much more time comparing to second one.

What I did to test that:

1. Implemented simple self hosted WCF Server and console client.
2. Server IS warmed up - I run it and call method several times before running test.
3. Binding is basicHttpBinding to reduce network and security overhead.
4. Testing scenario - start console client app, making two identical WCF service calls in a row.

In my tests I see ~700 milliseconds for first call and ~3 milliseconds for second call.

Almost a second seems to be too much time for JIT compiler. I would accept if that time is used to initialize some complicated infrastructure like ObjectContext in Entity Framework but my code is very simple and proxy classes are already compiled.

I also tried netNamedPipeBinding binding. Result proves pattern - first call takes ~800 ms, second call takes ~8 ms.

Will appreciate if anybody can explain why the first service call takes so much time.

Tested in Win 7 64 bit.

My implementation is below.

Contract:

[ServiceContract]
public interface ICounter
{
        [OperationContract]
        int Add(int num);
}

Service Implementation:

public class CounterService: ICounter
{
        private int _value = 0;

        public int Add(int num)
        {
            _value += num;
            Console.WriteLine(\"Method Add called with argument {0}. Method  returned {1}\", num, _value);
            return _value;
        }
}

Server Implementation:

class Program
{
    static void Main(string[] args)
    {
        Uri baseAddress = new Uri(\"http://localhost:8080/Service\");

        // Create the ServiceHost.
        using (ServiceHost host = new ServiceHost(typeof(CounterService), baseAddress))
        {
            host.Open();

            Console.WriteLine(\"The service is ready at {0}\", baseAddress);
            Console.WriteLine(\"Press <Enter> to stop the service.\");
            Console.ReadLine();

            // Close the ServiceHost.
            host.Close();
        }
    }
}

Server Configuration:

<?xml version=\"1.0\" encoding=\"utf-8\" ?>
<configuration>
  <system.serviceModel>
    <services>
      <service name=\"Server.CounterService\">
        <endpoint address=\"base\" binding=\"basicHttpBinding\" name=\"baseDefault\"
          contract=\"Contract.ICounter\" />
        <endpoint address=\"net.pipe://localhost/Service/netNamedPipe\"
          binding=\"netNamedPipeBinding\" name=\"netNamedPipeDefault\" contract=\"Contract.ICounter\" />
        <endpoint address=\"mex\" binding=\"mexHttpBinding\" contract=\"IMetadataExchange\" />
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name=\"\">
          <serviceMetadata httpGetEnabled=\"true\" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>

Client Implementation (CounterProxy is generated from service reference):

Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();

using (var proxy = new CounterProxy.CounterClient(_endpointConfigurationName))
{
    output = proxy.Add(1);
}

stopWatch.Stop();
// Get the elapsed time as a TimeSpan value.
TimeSpan ts = stopWatch.Elapsed;

Function that contains that code called two times in a row.

Client Configuration:

<?xml version=\"1.0\" encoding=\"utf-8\" ?>
<configuration>
  <system.serviceModel>
    <client>
      <endpoint address=\"http://localhost:8080/Service/base\" binding=\"basicHttpBinding\"
          contract=\"CounterProxy.ICounter\"
          name=\"baseDefault\" />
    </client>
  </system.serviceModel>
</configuration>

回答1:

Usually the first call takes more time because in that call the Channel Factory is instantiated and prepared ready for the communication and that costs time. The created Channel Factory will be cached and reused in subsequent calls and so the time will be less.

http://social.msdn.microsoft.com/Forums/en/wcf/thread/43f89088-546b-46b0-adf8-214deb1741bd

回答2:

I have similar problem. So what we actually did, we wrote service that invoke WCF service per some interval. I know that it's not an elegant solution but it's working.

回答3:

If you are making calls to your WCF service less frequently than 15 seconds (we observed needing to wait about 20 seconds in our application), this Microsoft blog appears to explain your problem: http://blogs.msdn.com/b/wenlong/archive/2010/02/11/why-does-wcf-become-slow-after-being-idle-for-15-seconds.aspx

The article also links to this entry which mentions a fix for SetMinThreads() which also appears to be a contributing problem: http://blogs.msdn.com/b/wenlong/archive/2010/02/11/why-are-wcf-responses-slow-and-setminthreads-does-not-work.aspx

回答4:

I was seeing delays in the range of 30 seconds when I was first creating my service proxy instance which I knew must be related to some sort of network timeout.

In the end for me it was actually checks for the Certificate Revocation List that were being blocked or frustrated by the corporate proxy (yay Websense) as highlighted here: WCF service startup too slow? Have you thought to CRL check?.

For future reference and in case the link goes dead it came down to adding the following to the client config:

<configuration>
  <runtime>
    <generatePublisherEvidence enabled=“false”/>
  </runtime>
</configuration>

来源：https://stackoverflow.com/questions/10859832/why-is-the-first-wcf-client-call-slow