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Performance Counters and In-Process Side-By-Side Applications

Using the Performance Monitor (Perfmon.exe), it is possible to differentiate the performance counters on a per-runtime basis. This topic describes the registry change needed to enable this functionality.

By default, the Performance Monitor displays performance counters on a per-application basis. However, there are two scenarios in which this is problematic:

  • When you monitor two applications that have the same name. For example, if both applications are named myapp.exe, one will be displayed as myapp and the other as myapp#1 in the Instance column. In this case, it is difficult to match a performance counter to a particular application. It is not clear whether the data collected for myapp#1 refers to the first myapp.exe or the second myapp.exe.

  • When an application uses multiple instances of the common language runtime. The .NET Framework version 4 supports in-process side-by-side hosting scenarios; that is, a single process or application can load multiple instances of the common language runtime. If a single application named myapp.exe loads two runtime instances, by default, they will be designated in the Instance column as myapp and myapp#1. In this case, it is not clear whether myapp and myapp#1 refer to two applications with the same name, or to the same application with two runtimes. If multiple applications with the same name load multiple runtimes, the ambiguity is even greater.

You can set a registry key to eliminate this ambiguity. For applications developed using the .NET Framework 4, this registry change adds a process identifier followed by a runtime instance identifier to the application name in the Instance column. Instead of application or application#1, the application is now identified as application_pprocessID_rruntimeID in the Instance column. If an application was developed using a previous version of the common language runtime, that instance is represented as application_pprocessID provided that the .NET Framework 4 is installed.

To handle performance counters for multiple common language runtime versions that are hosted in a single application, you must change a single registry key setting, as shown in the following table.

Key name


Value name


Value type



1 (0x00000001)

A value of 0 for ProcessNameFormat indicates that the default behavior is enabled; that is, Perfmon.exe displays performance counters on a per-application basis. When you set this value to 1, Perfmon.exe disambiguates multiple versions of an application and provides performance counters on a per-runtime basis. Any other value for the ProcessNameFormat registry key setting is unsupported and reserved for future use.

After you update the ProcessNameFormat registry key setting, you must restart Perfmon.exe or any other consumers of performance counters so that the new instance naming feature works correctly.

The following example shows how to change the ProcessNameFormat value programmatically.

// Create or open registry key.
Microsoft.Win32.RegistryKey key; 
key = Microsoft.Win32.Registry.LocalMachine.CreateSubKey( 
// Create or overwrite value.
key.SetValue("ProcessNameFormat", 1, 

When you make this registry change, Perfmon.exe displays the names of applications that target the .NET Framework 4 as application_pprocessID_rruntimeID, where application is the name of the application, processID is the application's process identifier, and runtimeID is a common language runtime identifier. For example, if an application named myapp.exe loads two instances of the common language runtime, Perfmon.exe may identify one instance as myapp_p1416_r10 and the second as myapp_p3160_r10. The runtime identifier only disambiguates the runtimes within a process; it does not provide any other information about the runtime. (For example, the runtime ID has no relation to the version or the SKU of the runtime.)

If the .NET Framework 4 is installed, the registry change also affects applications that were developed using earlier versions of the .NET Framework. These appear in Perfmon.exe as application_pprocessID, where application is the application name and processID is the process identifier. For example, if the performance counters of two applications named myapp.exe are monitored, one might appear as myapp_p23900 and the other as myapp_p24908.


The process identifier eliminates the ambiguity of resolving two applications with the same name that use earlier versions of the runtime. A runtime identifier is not required for previous versions, because previous versions of the common language runtime do not support side-by-side scenarios.

If the .NET Framework 4 is not present or was uninstalled, setting the registry key has no effect. This means that two applications with the same name will continue to appear in Perfmon.exe as application and application#1 (for example, as myapp and myapp#1). 

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