What is Throttling Behavior in WCF?

WCF throttling provides some properties that you can use to limit how many instances or sessions are created at the application level. Performance of the WCF service can be improved by creating proper instance.

Attribute	Description
maxConcurrentCalls	Limits the total number of calls that can currently be in progress across all service instances. The default is 16.
maxConcurrentInstances	The number of InstanceContext objects that execute at one time across a ServiceHost. The default is Int32.MaxValue.
maxConcurrentSessions	A positive integer that limits the number of sessions a ServiceHost object can accept. The default is 10.

Service Throttling can be configured either Adminstractive or Programatically

Administrative (configuration file)

Using <serviceThrottling> tag of the Service Behavior, you can configure the maxConcurrentCalls, maxConcurrentInstances , maxConcurrentSessions property as shown below.

<system.serviceModel>

    <services >

      <service behaviorConfiguration="ServiceBehavior"  name="MyService">

        <endpoint address="" binding="wsHttpBinding" contract="IMyService">

          <identity>

            <dns value="localhost"/>

          </identity>

        </endpoint>

        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange"/>

      </service>

    </services>

    <behaviors>

      <serviceBehaviors>

        <behavior name="ServiceBehavior">

          <serviceMetadata httpGetEnabled="true"/>

          <serviceDebug includeExceptionDetailInFaults="true "/>

          <serviceThrottling maxConcurrentCalls="500"

 maxConcurrentInstances ="100" 

maxConcurrentSessions ="200"/>

        </behavior>

      </serviceBehaviors>

    </behaviors>

  </system.serviceModel>

Programming Model:

Use ServiceThrottlingBehavior object to set concurrent calls, session and instance property.

           ServiceHost host = new ServiceHost(typeof(MyService)); 

          ServiceThrottlingBehavior throttle = host.Description.Behaviors.Find();

            if (throttle == null)

            {

                throttle = new ServiceThrottlingBehavior();

                throttle.MaxConcurrentCalls = 500;

                throttle.MaxConcurrentSessions = 200;

                throttle.MaxConcurrentInstances = 100;

                host.Description.Behaviors.Add(throttle);

            }

            host.Open();