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FIX: You experience performance issues when you run a .NET Framework 3.5-based WCF service that uses TCP transport and enables channel caching under heavy load conditions

Consider the following scenario. You use a Microsoft .NET Framework 3.5-based Windows Communication Foundation (WCF) service that uses TCP transport for communication. Then, you enable channel caching, for example, by using the OneWayBindingElement class to pool the TCP channels. In this scenario, when the service runs under heavy load conditions, you notice two performance issues:
  • The thread pool on the server becomes exhausted and the service may stop responding.
  • When the WCF clients send messages to an endpoint, a time-out issue occurs.
These problems occur because the asynchronous calls that WCF uses are blocked. When I/O requests occurs under heavy load conditions, the blocked threads cause the Common Language Runtime (CLR) thread to input additional threads into the thread pool. However, the rate of thread input causes the I/O requests to time-out.
Note If you are using the .NET Framework 3.5 Service Pack 1 on Windows 7 or on Windows Server 2008 R2, install the hotfix that is described in the following Microsoft Knowledge Based article:
977420 A hotfix rollup is available to fix problems in Windows Communication Foundation in the .NET Framework 3.5 SP1 for Windows 7 and for Windows Server 2008 R2

Hotfix information

A supported hotfix is now available from Microsoft. However, it is intended to correct only the problem that this article describes. Apply it only to systems that are experiencing this specific problem.

To resolve this problem, contact Microsoft Customer Support Services to obtain the hotfix. For a complete list of Microsoft Customer Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.


You must have Microsoft .NET Framework 3.5 Service Pack 1 (SP1) installed on Windows Vista Service Pack 2 (SP2) or Windows Server 2008 SP2 to apply this hotfix.

Restart requirement

You do not have to restart the computer after you install the hotfix if no relative .NET Framework instance is in use.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
x86-based version for Windows Vista SP2 and Windows Server 2008 SP2
File nameFile versionFile sizeDateTimePlatform

x64-based version of Windows Vista SP2 and Windows Server 2008 SP2
File nameFile versionFile sizeDateTimePlatform

Itanium-based version of Windows Server 2008 SP2
File nameFile versionFile sizeDateTimePlatform
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

Article ID: 971841 - Last Review: 03/01/2011 06:29:00 - Revision: 2.0

  • Microsoft .NET Framework 3.5
  • Microsoft .NET Framework 3.5 Service Pack 1
  • kbexpertiseadvanced kbsurveynew kbqfe KB971841
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