Windows – Can an IIS worker process’s Virtual Memory use exceed the Private Memory limit

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For example, if I configure the following limits for an Application Pool in the "Recycling" settings:

Virtual Memory: 512Mb
Private Memory: 128Mb – or "used memory" in IIS 6 parlance

Can the process use, say, 90Mb of physical memory but have requested the use of 256Mb of Virtual memory and thus not trigger a recycle?

Best Answer

Yes It would be common for an IIS worker process to use more virtual memory than physical memory. To see for yourself download a copy of ProcessExplorer and look at the process memory of one of the IIS worker processes.

As an example from the below screen capture, from ProcessExplorer on an IIS 6 Server, you can see that this IIS worker process is using ~195MB of Virtual Memory and ~37MB of Physical Memory (Working Set).

For an explanation of the relationship between the different memory types see this StackOVerflow question What is private bytes, virtual bytes, working set?

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So based on the limits you have configured using a IIS Worker Process that is using 90MB of Physical and 256MB of Virtual wouldn't trigger a recycle of the Application Pool.

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