IIS 7.x : Different ways in which Kernel Mode Cache would be flushed

by jask2002 20. January 2012 07:37

 

Based on my own experience following are the different ways which would trigger flushing of Kernel mode cache

 

1) Time to live: Set by Expire Header in response or Time set through cache time policy

 

2) Application Domain restart: Even if PID is same for w3wp.exe, App Domain shutdown can occur due to various reasons and that would flush Kernel mode cache

 

3) URIScavenger : 120 seconds[Default value] of inactivity . Editable in registery

 

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters
Name: UriScavengerPeriod
Type: REG_DWORD
Data: 120 (seconds)

 

4) File Change Notification triggers flushing kernel mode cached URI. For example COPY/PASTE in root folder. FCn is aggresive in .Net 2.0.  Suggested Read

 

5) Explicitly deleting: Netsh http delete cache

 

C:\Windows\system32>netsh http show cachestate

 

Snapshot of HTTP response cache:
--------------------------------

 

URL: http://localhost:8081/welcome.png
Status code: 200
HTTP verb: GET
Cache policy type: User invalidates
Creation time: 2010.9.24:15.12.22:0
Request queue name: Mine
Content type: image/png
Content encoding: (null)
Headers length: 211
Content length: 217523
Hit count: 2
Force disconnect after serving: FALSE

 

C:\Windows\system32>netsh http delete cache http://localhost:8081/welcome.png
Ok.

 


6) On-Demand - ISAPI Extension can use the HSE_REQ_GET_CACHE_INVALIDATION_CALLBACK ServerSupportFunction to retrieve a pointer to the on-demand URL revocation function, and you call this function pointer with the FULL URL (obtained via the UNICODE_CACHE_URL ServerVariable when you cached that URL's response to begin with) to evict that URL's cached response.

 

7) IISRESET/Server reboot would flush http.sys kernel mode cache

 

8) When the AppPool is explicitly stopped in IIS. This would also flush kernel mode cache

 

9) When system is low on physical RAM. HTTP.Sys can flush the kernel mode cache. /3 GB switch would have direct impact on it

 

 Hope this helps.. Laughing


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Tags: , ,

IIS 7 | http.sys | Cache

Comments (2) -

Arvind
Arvind India
7/27/2012 2:36:39 AM #

Brilliant post! Thank you Jaskirat!

Reply

Arnulfo Pazo
Arnulfo Pazo United States
8/31/2013 4:41:08 AM #

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About me

Hi there,

My name is  Jas and I'm currently working with Microsoft IIS/ASP.Net Escalation services.  Services

 

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The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.