As Support Engineer, I have the possibility to work with many customers around the world with different configurations. A couple of mounts ago, I was surprised to work with one of them who sustained that after the migration to IIS7 from IIS6, the IIS7’s performance was worse than IIS6. The servers’ goal was the same: both of them access on the same remote share in order to provide images to final users. It means no custom code was in execution: final users have the possibility to get their images simply opening urls like this one http://serverName/myImage.jpg on their brewers.
How was it possible? Was really IIS7 performing worse than IIS6? Of course no! The remote server (where the images were stored on) was the same for both web servers: IIS6 and II7. The network was working properly, let’s say with the same bandwidth, so where the issue was!?!
After collecting a memory dump, everything was clear (as in most of cases ). Well the threads were like this one:
0:087> k # ChildEBP RetAddr 00 0671ed44 75c63bc8 ntdll!ZwDelayExecution+0x15 01 0671edac 75c64498 KERNELBASE!SleepEx+0x65 02 0671edbc 73c48765 KERNELBASE!Sleep+0xf 03 0671edf0 73c443c4 iisutil!CReaderWriterLock3::_LockSpin+0xfb 04 0671ee10 73beeb73 iisutil!CReaderWriterLock3::ReadLock+0x3c 05 0671ee18 73bf1b1b nativerd!CONFIG_CACHE::ReadLock+0x11 06 0671ee28 73bdaad0 nativerd!CONFIG_CACHE::GetConfigFileList(class PATH * pConfigPath = 0x0671ef14, unsigned long dwParseMode = 0x2a, class CONFIG_FILE_LIST * pConfigFileList = 0x0671ee4c, class PARSE_ERROR_INFO * pParseErrorInfo = 0x0671f0b8)+0xe 07 0671f26c 73bb896d nativerd!CONFIG_SYSTEM::GetUniqueConfigPath(wchar_t * bstrConfigPath = 0x0671f598 "MACHINE/WEBROOT/APPHOST/SFTBS.SL.PT/auto/media/000561/Viaturas/000714130/166x125/Renault-Laguna-2357165.jpg", wchar_t ** pbstrUniquePath = 0x0671f290)+0xba 08 0671f294 730a3ca5 nativerd!CONFIG_SYSTEM::GetUniqueConfigPath(wchar_t * pszConfigPath = 0x0671f598 "MACHINE/WEBROOT/APPHOST/SFTBS.SL.PT/auto/media/000561/Viaturas/000714130/166x125/2357165.jpg", wchar_t * pszUniqueConfigPath = 0x0671f798 "", unsigned long * pcchUniqueConfigPath = 0x0671f2c0, class INativeSectionException ** ppException = 0x0671f9c4)+0x2809 0671f99c 730a547d iiscore!W3_CONTEXT::SetupMetadata+0x22b 0a 0671f9d0 730a5ab3 iiscore!W3_CONTEXT::SetupStateMachinePhase2+0x7e 0b 0671fa44 730a61c3 iiscore!W3_CONTEXT::SetupStateMachine+0x241 0c 0671fa58 730a6642 iiscore!W3_MAIN_CONTEXT::StartNotificationLoop+0x3f 0d 0671fa70 72ea1568 iiscore!W3_MAIN_CONTEXT::OnNewRequest+0x47 0e 0671fa7c 72ea14e6 w3dt!UL_NATIVE_REQUEST::DoStateProcess+0x26 0f 0671fa88 72ea154c w3dt!UL_NATIVE_REQUEST::DoWork+0x60 10 0671fa9c 7324265a w3dt!OverlappedCompletionRoutine+0x1a 11 0671fad4 7324289a w3tp!THREAD_POOL_DATA::ThreadPoolThread+0x89 12 0671fae8 73241e95 w3tp!THREAD_POOL_DATA::ThreadPoolThread+0x24 13 0671fb00 75b533aa w3tp!THREAD_MANAGER::ThreadManagerThread+0x39 14 0671fb0c 778a9ef2 kernel32!BaseThreadInitThunk+0xe 15 0671fb4c 778a9ec5 ntdll!__RtlUserThreadStart+0x70 16 0671fb64 00000000 ntdll!_RtlUserThreadStart+0x1b
What were they doing? They were trying to get a configuration file. The fact is this one:
- Starting form IIS 7, the web server’s pipeline changed including new features and new integration with .NET.
Even if customer was not using any feature of ASP.Net (consider that his app is sharing images over the web) IIS was looking for web.config files at every content level on the file server.
- The problem was there, customer file server was hosting hundreds and hundreds of folders, so the constant work to research web.config files caused the bottleneck.
What was the resolution? We have two possible resolutions here:
- We could configure IIS in order to research webConfig file every 10 minutes for example. To do that we have to set the following registry key as mentioned below:
HKLM\System\CurrentControlSet\Services\W3SVC\Parameters\ConfigPollMilliSeconds = 600000
Further details here: http://support.microsoft.com/kb/954864
Of course this setting is not related to a single web application, it has an impact on web server.
This solution could not work for all web applications installed on your IIS, furthermore a new change on your webConfig will be not reflected
- This is my preferred solution, read here: http://www.iis.net/configreference/system.applicationhost/sites/site/application/virtualdirectory
“Optional Boolean attribute.
Specifies whether IIS looks for Web.config files in content directories lower than the current level (true) or does not look for Web.config files in content directories lower than the current level (false).
The default value is true.”
If you change the value of allowSubDirConfig to false in every application’s root, our goal is achieved: IIS will stop to research for web config file stored on application’s subfolder.
What happened at the end… J IIS7 worked 5 times faster than IIS6 on customer’s environment.