Optimizing WCF Services for Performance and Scalability

Increasing Concurrency for Better Performance

1. Choosing the Right WCF Binding

Choosing the appropriate WCF binding significantly impacts performance. For example, while WSHttpBinding includes support for security, reliable sessions, and transaction flow, it comes with additional overhead. Switching to BasicHttpBinding can greatly enhance performance when these features are not required.

2. Throttling

Throttling is crucial for WCF performance tuning, allowing control over service load through properties like maxConcurrentCalls, maxConcurrentInstances, and maxConcurrentSessions, which limit the number of instances or sessions at the application level.

Configuring the ServiceThrottlingBehavior appropriately can dramatically improve service throughput.

<configuration>
  <system.serviceModel>
    <services>
      <service
        <!-- Service configuration -->
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="ServiceBehavior">
          <serviceThrottling
            maxConcurrentCalls="16" maxConcurrentSessions="100" maxConcurrentInstances="10" />
          <serviceMetadata httpGetEnabled="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>

3. Choose the Right Instance Context Mode

The InstanceContextMode directly influences service scalability. WCF offers three options:

• PerCall: Creates a new instance of the service for each request.
• PerSession: Maintains a single service instance for the duration of a client session.
• Singleton: Uses a single service instance for all requests, which is suitable for stateful services but may lead to bottlenecks under high load.

For optimal concurrency, PerCall or PerSession is recommended, depending on the session requirements of your service.

Efficient Use of PerCall Mode

Avoid heavy initialization in the parameterless constructor:

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class MyService : IMyService
{
    private static readonly MyReferenceData ReferenceData = LoadReferenceData();

    public MyService()
    {
        // Minimal constructor logic
    }

    public MyReferenceData GetReferenceData() => ReferenceData;
}

Alternatively, use a wrapper to handle complex initialization or dependency injection:

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]
public class MyServiceWrapper : IMyServiceWrapper
{
    private static readonly IMyService ServiceInstance = _container.Resolve<IMyService>();

    public void DoSomething() => ServiceInstance.DoSomething();
}

public interface IMyServiceWrapper : IMyService {}

4. Increase Idle I/O Threads

Concurrency in WCF services often hinges on the availability of I/O threads. By default, the ThreadPool maintains one idle I/O thread per CPU. When additional threads are required, they are created with a delay, which can cause bottlenecks during sudden bursts of activity.

To address this, adjust the minimum number of idle threads using ThreadPool.SetMinThreads:

ThreadPool.SetMinThreads(workerThreads, ioThreads);

5. Use data contract serialization

Serialization converts objects into transferable formats, with XML serialization offering interoperability and binary serialization suited for .NET-to-.NET communication. Data contract serialization, which supports public, private, and protected members, is about 10% faster than XML serialization, making it ideal for handling large data volumes efficiently.

6. Caching

External dependencies are a significant challenge to WCF service performance. Caching can help overcome this issue by storing frequently accessed data in memory or another fast retrieval location.

Two common caching options are in-memory caching and external caching.

In-memory Caching:

By default, WCF services cannot access the ASP.NET cache.

However, enabling ASP.NET compatibility with the AspNetCompatibilityRequirements attribute allows WCF services to use the ASP.NET cache.

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
<system.serviceModel>
    <!-- Other service model configuration -->
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" />
    <!-- Other service model configuration -->
</system.serviceModel>

External Caching:

A challenge with in-memory caching is managing cache expiration when data is updated. This can be addressed using sticky sessions, where requests from the same source IP are directed to the same server. Additionally, Windows Server AppFabric can be utilized as an external caching solution to improve performance.

7. Close Proxy Connections

It's essential to always close the proxy connection when the client is done using it. Closing the proxy connection ensures that the service's session expires, and the connection between the server and client is properly terminated.

// Create the service proxy
MyServiceClient client = new MyServiceClient();

// Use the service
client.DoSomething();

// Close the connection when done
client.Close(); // Ensures the session is closed and resources are released

In this example, calling client.Close() terminates the session and closes the connection between the client and the server, ensuring that resources are freed and no lingering sessions remain.

8. Compress data

Only serialize the data that is necessary for the end user and required for transmission. In other words, avoid sending unnecessary data over the network.