PowerShell leaking memory when using IIS cmdlets

We are having issues with the IIS cmdlets being used in WinRS, requiring an increased value of the MaxMemoryPerShellMB setting.

We get a bunch of random errors each time we hit the limit and we identified the problem by monitoring the memory of the wsmprovhost processes. 

Since we are creating many things in one wsmprovhost process (sites, applications and application pools) I do not know what all the calls are that are leaving allocated memory behind. The following example of getting an application pool is just one of them.

Using:

Get-WebConfigurationProperty -filter "//site[@name='Default Web Site']/application" -Name applicationPool | select value -Unique

...will not cause the shell's allocated memory to increase so much. It also seems it decreases after a while and even when you force a GC.Collect.

However, with a small addition to the command above, this will leave allocated memory behind:

Get-WebConfigurationProperty -filter "//site[@name='Default Web Site']/application" -Name applicationPool | select value -Unique | %{ get-item (join-path "IIS:\AppPools" $_.value) }

To verify this behavior:

1. Set up two PSSessions to the target host with IIS installed

2. Monitor the wsmprovhost processes in one of the sessions by issuing the folllowing command:

 while(1) { Get-Process wsmprovhost; sleep 5 }

3. In the other session, call the memory leaking command in a loop:

1..1000 | %{ Get-WebConfigurationProperty -filter "//site[@name='Default Web Site']/application" -Name applicationPool | select value -Unique | %{ get-item (join-path "IIS:\AppPools" $_.value) } }

4. You will now see the memory load increasing of one of the shells - something like this:

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
    303      26    59900      66636   583     0,42   4644 wsmprovhost
    301      25    59900      66656   583     0,42   4644 wsmprovhost
    342      27    62164      73400   584     0,69   4644 wsmprovhost
    342      27    62164      73400   584     0,69   4644 wsmprovhost
    342      27    62164      73400   584     0,69   4644 wsmprovhost
    342      27    62164      73400   584     0,69   4644 wsmprovhost
    342      27    62164      73400   584     0,69   4644 wsmprovhost
    339      27    62080      73384   584     0,69   4644 wsmprovhost
    339      27    62080      73384   584     0,69   4644 wsmprovhost
    339      27    62080      73384   584     0,69   4644 wsmprovhost
    339      27    62080      73384   584     0,69   4644 wsmprovhost
    339      27    62080      73384   584     0,69   4644 wsmprovhost
    339      27    62080      73384   584     0,69   4644 wsmprovhost
    384      32    66620      82612   603     1,20   4644 wsmprovhost
    459      33   117036     131920   616     4,56   4644 wsmprovhost
    405      33   130692     145848   616     8,19   4644 wsmprovhost
    395      33   184864     200212   616    11,79   4644 wsmprovhost
    386      33   260608     271436   751    15,40   4644 wsmprovhost
    389      32   336288     348812   757    19,34   4644 wsmprovhost
    382      32   421332     433764   898    23,26   4644 wsmprovhost
    382      32   526912     529696  1040    27,14   4644 wsmprovhost
    379      32   623264     626392  1040    31,34   4644 wsmprovhost
    395      34   669152     672440  1170    33,31   4644 wsmprovhost
    405      34   669160     672488  1170    33,32   4644 wsmprovhost
    405      34   669160     672488  1170    33,32   4644 wsmprovhost
    407      34   669160     672504  1170    33,32   4644 wsmprovhost

I was able to get a local (not using WinRS) powershell instance eat 1600 MB of RAM using the loop above.

We have used our script since Server 2003 and PowerShell v1 and never had any issues with this. When we upgraded to Server 2008 R2 we needed to increase the MaxMemoryPerShellMB setting from 150 to 512. 

Yesterday we pushed out a release which included one more application and application pool and we hit the limit again. We was able to work around this problem by increasing the setting up to 1024 MB.

As you can see it was quite easy for me to push it over a 512 MB limit just by using Get-Item on an application pool.

Why is the Get-Item command causing this? Should I avoid it and use, where possible, Get-WebConfigurationXX cmdlets instead?

Thanks in advance for your assistance!

Best regards, 

Johan Andersson

https://github.com/anderssonjohan