Handling Duplicate Instance Names

Although providers are strongly encouraged to use unique instance names, not all providers do. The convention for displaying duplicate instance names is to append a # character and a serial number to the instance name, except for the first occurrence of the name. For example, if there are three instances of svchost in a sample, the three names are displayed as svchost, svchost#1, and svchost#2.

Unfortunately, this convention does not completely resolve the issue. Serial numbers are assigned based on the order in which a particular instance name appears in a sample, and this order may be inconsistent from sample to sample. For example, sample A might see svchost (PID 100), svchost#1 (PID 200), and svchost#2 (PID 300). Then if the svchost with PID 100 shuts down, the next sample would see svchost (PID 200) and svchost#1 (PID 300). Basic matching logic would try to match sample A's svchost#1 statistics (from PID 200) against sample B's svchost#1 statistics (from PID 300), resulting in invalid results for sample B. Errors occur when a new non-unique instance shows up in a sample or when a non-unique instance stops showing up in a sample (unless the added/removed instance was the last one).

Process counterset

This issue is especially problematic for the Process counterset because it uses only the process's EXE name as the instance name even though the EXE name is not unique. The default behavior of the Process counterset on Windows cannot be changed due to compatibility issues.


Windows 11 and later include the new Process V2 counterset. The Process V2 counterset includes the process ID (PID) in the instance name which avoids the name duplication issue of the Process counterset.

You can alter the behavior of the Process and Thread countersets to use unique instance names by setting the ProcessNameFormat or ThreadNameFormat registry values under the HKLM\System\CurrentControlSet\Services\Perfproc\Performance registry key.


Enabling unique instance names for the Process counterset may cause some programs to behave incorrectly, since many programs expect the non-unique naming pattern. For example, a program that is looking for an instance with a specific well-known EXE name will no longer be able to find that instance after enabling unique instance names.

The registry type for these values is REG_DWORD. Setting the value to 2 appends the process identifier (PID) to the process instance name and the thread identifier (TID) to the thread instance name. To disable this feature, set the value to 1 or delete the value.