限制 ASP.NET 应用程序与 Web 服务同时连接的 # 是什么？

我有一个 ASP.NET 4.0应用程序运行在 IIS 7.5之上，在一台64位 Windows Server 2008 R2的企业级机器上，这台机器有大量的内存、 CPU、磁盘等。

对于每个 Web 请求，ASP.NET 应用程序都会连接到一个后端 Web 服务(通过原始套接字) ，该服务在同一台机器上运行。

问题: 似乎有什么东西限制了 # 到后端 Web 服务的同时连接。令人怀疑的是，并发连接的数量已经超过了16个。

我从微软找到了这篇关键文章，解释了如何调整 IIS 的设置，以适应发出大量 Web 服务请求的 ASP.NET 应用程序: http://support.microsoft.com/?id=821268#tocHeadRef

我按照那篇文章的建议做了，但还是没有收获。特别有趣的设置是 maxconnection设置，我甚至把它调到了999。

你知道 别的是怎么控制连接的吗？

注意: 当我把 IIS 从混合中删除，让客户端直接连接到后端 Web 服务时，它会很高兴地打开我需要的任意多个连接，所以我肯定后端不是瓶颈。它一定是 IIS/ASP.NET 中的某种东西。

下面是 machine.config的相关部分，我确信应用程序正在阅读它(用 appcmd.exe验证) :

<system.web>
<processModel autoConfig="false" maxWorkerThreads="100" maxIoThreads="100" minWorkerThreads="50" />
<httpRuntime minFreeThreads="176" minLocalRequestFreeThreads="152"/>


<httpHandlers />


<membership>
<providers>
<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="" />
</providers>
</membership>


<profile>
<providers>
<add name="AspNetSqlProfileProvider" connectionStringName="LocalSqlServer" applicationName="/"
type="System.Web.Profile.SqlProfileProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
</providers>
</profile>


<roleManager>
<providers>
<add name="AspNetSqlRoleProvider" connectionStringName="LocalSqlServer" applicationName="/"
type="System.Web.Security.SqlRoleProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
<add name="AspNetWindowsTokenRoleProvider" applicationName="/"
type="System.Web.Security.WindowsTokenRoleProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
</providers>
</roleManager>
</system.web>
<system.net>
<connectionManagement>
<add address="*" maxconnection="999"/>
</connectionManagement>
</system.net>
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小开

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?

小开

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

小开

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 <serviceThrottling> element

<serviceThrottling
maxConcurrentCalls="999"
maxConcurrentSessions="999"
maxConcurrentInstances="999" />

(Note that I'd recommend the settings above.) See MSDN for more information how to configure an appropriate <behavior> element.

小开

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.

小开

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:

<configuration>
<system.net>
<connectionManagement>
<add address="*" maxconnection="65535"/>
</connectionManagement>
</system.net>
</configuration>

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
小开

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

小开

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: <remove> Element for connectionManagement (Network Settings)

Hope it helps someone.


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