What is limiting the of simultaneous connections my ASP NET application can make to a web service

Question

I have an ASP NET 4 0 application running atop IIS 7 5 on a 64-bit Windows Server 2008 R2 Enterprise machine with gobs of RAM  CPU  disk  etc   With every web request  the ASP NET application makes a connection to a backend web service  via raw sockets   which is running on the same machine   Problem  There appears to be something limiting the   of simultaneous connections to the backend web service   Suspiciously  the number of concurrent connections is topping out at 16   I found this key article from Microsoft explaining how to tweak IIS  settings to accomodate ASP NET apps that make lots of web service requests  http   support microsoft com  id 821268 tocHeadRef  I followed the article s recommendatinos  but still no luck   The setting that is particularly interesting is the maxconnection setting  which I even bumped to 999   Any ideas what else could be throttling connections   Note  When I cut IIS out of the mix and have the clients connect directly to the backend web service  it will happily open as many connections as I need  so I m positive the backend is not the bottleneck   It must be something in IIS ASP NET-land   Here s the relevant section of the machine config which I m sure is being read by the application  verified with appcmd exe     lt system web gt       lt processModel autoConfig  false  maxWorkerThreads  100  maxIoThreads  100  minWorkerThreads  50    gt       lt httpRuntime minFreeThreads  176  minLocalRequestFreeThreads  152   gt        lt httpHandlers   gt        lt membership gt           lt providers gt               lt add name  AspNetSqlMembershipProvider                  type  System Web Security SqlMembershipProvider  System Web  Version 4 0 0 0  Culture neutral  PublicKeyToken b03f5f7f11d50a3a                  connectionStringName  LocalSqlServer                  enablePasswordRetrieval  false                  enablePasswordReset  true                  requiresQuestionAndAnswer  true                  applicationName                     requiresUniqueEmail  false                  passwordFormat  Hashed                  maxInvalidPasswordAttempts  5                  minRequiredPasswordLength  7                  minRequiredNonalphanumericCharacters  1                  passwordAttemptWindow  10                  passwordStrengthRegularExpression      gt           lt  providers gt       lt  membership gt        lt profile gt           lt providers gt               lt add name  AspNetSqlProfileProvider  connectionStringName  LocalSqlServer  applicationName                     type  System Web Profile SqlProfileProvider  System Web  Version 4 0 0 0  Culture neutral  PublicKeyToken b03f5f7f11d50a3a    gt           lt  providers gt       lt  profile gt        lt roleManager gt           lt providers gt               lt add name  AspNetSqlRoleProvider  connectionStringName  LocalSqlServer  applicationName                     type  System Web Security SqlRoleProvider  System Web  Version 4 0 0 0  Culture neutral  PublicKeyToken b03f5f7f11d50a3a    gt               lt add name  AspNetWindowsTokenRoleProvider  applicationName                     type  System Web Security WindowsTokenRoleProvider  System Web  Version 4 0 0 0  Culture neutral  PublicKeyToken b03f5f7f11d50a3a    gt           lt  providers gt       lt  roleManager gt   lt  system web gt   lt system net gt       lt connectionManagement gt           lt add address     maxconnection  999   gt       lt  connectionManagement gt   lt  system net gt

User · Answer

See the  Threading  section of this page  http   msdn microsoft com en-us library ff647786 aspx  in conjunction with the  Connections  section   Have you tried upping the maxconnection attribute of your processModel setting

User · Answer

Most of the answers provided here address the number of incoming requests to your backend webservice  not the number of outgoing requests you can make from your ASP net application to your backend service   It s not your backend webservice that is throttling your request rate here  it is the number of open connections your calling application is willing to establish to the same endpoint  same URL    You can remove this limitation by adding the following configuration section to your machine config file    lt configuration gt     lt system net gt       lt connectionManagement gt         lt add address     maxconnection  65535   gt       lt  connectionManagement gt     lt  system net gt   lt  configuration gt    You could of course pick a more reasonable number if you d like such as 50 or 100 concurrent connections  But the above will open it right up to max  You can also specify a specific address for the open limit rule above rather than the     which indicates all addresses   MSDN Documentation for System Net connectionManagement  Another Great Resource for understanding ConnectManagement in  NET  Hope this solves your problem   EDIT  Oops  I do see you have the connection management mentioned in your code above  I will leave my above info as it is relevant for future enquirers with the same problem  However  please note there are currently 4 different machine config files on most up to date servers   There is  NET Framework v2 running under both 32-bit and 64-bit as well as  NET Framework v4 also running under both 32-bit and 64-bit  Depending on your chosen settings for your application pool you could be using any one of these 4 different machine config files  Please check all 4 machine config files typically located here    C  Windows Microsoft NET Framework v2 0 50727 CONFIG C  Windows Microsoft NET Framework64 v2 0 50727 CONFIG C  Windows Microsoft NET Framework v4 0 30319 Config C  Windows Microsoft NET Framework64 v4 0 30319 Config

User · Answer

while doing performance  testing  the measure i go by is RPS  that is how many requests per second can the server serve within acceptable latency   theoretically one server can only run as many requests concurrently as number of cores on it    It doesn t look like the problem is ASP net s threading model  since it can potentially serve thousands of rps  It seems like the problem might be your application  Are you using any synchronization primitives     also whats the latency on your web services  are they very quick to respond  within microseconds   if not then you might want to consider asynchronous calls  so you dont end up blocking   If this doesnt yeild something  then you might want to profile your code using visual studio or redgate profiler

User · Answer

Might it be possible that you re using a WCF-based web service reference  By default  the ServiceThrottlingBehavior MaxConcurrentCalls is 16   You could try updating your service reference behavior s  lt serviceThrottling gt  element   lt serviceThrottling     maxConcurrentCalls  999       maxConcurrentSessions  999       maxConcurrentInstances  999    gt     Note that I d recommend the settings above   See MSDN for more information how to configure an appropriate  lt behavior gt  element

User · Answer

I realize the question might be rather old  but you say the backend is running on the same server  That means on a different port  probably other than the default port 80   I ve read that when you use the  connectionManagement  configuration element  you need to specify the port number if it differs from the default 80   LINK  maxConnection setting may not work even autoConfig   false in ASP NET  Secondly  if you choose to use the default configuration  address      extended with your own backend specific value  you might consider putting the specific value first  Otherwise  if a request is made  the   matches first and the default of 2 connections is taken  Just like when you use the  section in web config   LINK   lt remove gt  Element for connectionManagement  Network Settings   Hope it helps someone

User · Answer

Have you tried to set the value of the static DefaultConnectionLimit  property programmatically   Here is a good source of information about that true headache    ASP NET Thread Usage on IIS 7 5  IIS 7 0  and IIS 6 0  with updates for framework 4 0

User · Answer

If it is not defined in the web service or application or server  apache or IIS  that is hosting the web service consumable then you could create infinite connections until failure

[asp.net] What is limiting the # of simultaneous connections my ASP.NET application can make to a web service?

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