3 techniques for Instance management in WCF

By | September 10, 2013

Instance management basically defines the binding of service instance to a request received from a client. In case of WCF, following three techniques for service instantiation are available: 

  • PerCall
  • PerSession
  • Single
As we know that application requirements varies from one to another with respect to scalability, durability, performance, transactions etc, so in order to meet respective needs of the application, we chose between different WCF service instance modes and this is what we are going to discuss here in this WCF Tutorial.

“PerSession” is the default instance mode for WCF Service. In order to use any specific techniques mentioned above, we need to configure serviceBehavior attribute for a service as follows:
public interface IInstanceManagDemoService
string Method1();
public class InstanceManagDemoService : IInstanceManagDemoService
public string Method1()
//method details here…..
In case of PerCall Instance mode, a new instance is created against each request coming from client and later disposed off when response is sent back from service as shown in the following diagram.

Above diagram shows that all request coming from one or more clients are served by separate instance on server. 
Key points about this approach are follows:

  • We will prefer to use this approach when we don’t need to maintain state between requests.
  • Scalability is a major concern and service holds expensive resources like communication ports, files or database connections etc.

For PerSession Instance mode, a new instance is maintained on server for one session. For separate session, another instance is created that serves the request. Normally, we use this technique, when we need to maintain session between multiple requests.

Above diagram shows that for all requests from “WCF Client 1” are served by “Service Instance 1”. Same is the case for client 2 and client 3 respectively. In this technique, the service instance is disposed off when one a particular client completes its all method calls to perform a specific functionality.

Key points about this approach are follows:
  • Approach is preferable when we need to maintain state.
  • Scalability is a concern but not the biggest concern.

In case of Single/Singleton Instance mode, only one instance is created to serve all the requests coming from all clients.


In this technique, service instance is not disposed off and it stays on server to serve all incoming requests.

Key points about this approach are follows:
  • We want to share global data using service.
  • Scalability is not a concern at all.


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Imran Abdul Ghani is working as Software Developer(Senior) with extensive knowledge in Web development technologies especially C#, ASP.NET, MVC, WCF, Web API, ADO.NET Entity Framework, jQuery etc. He has several years of experience in designing/developing enterprise level applications. He is Microsoft Certified Solution Developer for .NET (MCSD.NET) since 2005. You can reach his blogging at www.webdevelopmenthelp.net, www.topwcftutorials.net, and www.sharepointfordummies.net.

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