WCF MaxConcurrentSessions exceeded

Question

I am hitting into a problem with my company application.

I am going to summarize the system key elements:

My company's system is running since few years on Windows XP and 7 (Home, Pro, Basic) machines.
It has been written in .NET 4.0 and based upon WCF.
It uses the default throttling values (MaxConcurrentSessions = 100 * CPU (4) : enough for our workload).
The main service is hosted by a stand alone deamon process (not IIS).
The main service is configured as Multithraded/PerSession instances.
The protocol is Reliable NET.TCP.
No more than 10 clients access concurrently the service.

The problem is that only on Windows 7, intermittently, I get (I discovered that by the WCF full trace log) a "Server too busy exception" due to an exhausted MaxConcurrentSessions limit (impossible!!!).

Do you have any idea about this strange behaviour?

Thank you and have a Happy New Year!

Antonio

The "Answer 2" provided by the link http://go4answers.webhost4life.com/Example/connect-busy-wcf-service-host-while-725.aspx maybe interesting... — Antonio Petricca, Dec 30 '13 at 16:10
You might want to try this. http://stackoverflow.com/q/2960056/1181408 — cgotberg, Dec 30 '13 at 16:32
Thank you very much cgotberg, but the ServicePoint concept is applicable only to HTTP connections, instead I'm using a NET.TCP one. — Antonio Petricca, Dec 30 '13 at 16:44
If you increase the `MaxConcurrentSessions` to a much highter value the problem persists? Maybe you have more concurrent sessions than you think in a given moment. — Vitor Canova, Dec 30 '13 at 19:03
Yes it persists, as I wrote the issue there is only on Windows 7! — Antonio Petricca, Dec 31 '13 at 08:40

score 1 · Answer 1 · answered Jan 20 '14 at 14:20

1

Do all your Clients properly close/dispose connection to service after use ? It's worth to check, "ghost" connections could maybe explain this.

answered Jan 20 '14 at 14:20

AFract

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1

The answer is a little short maybe (how to correctly close/abort...) but I would guess this is the underlying problem. – StampedeXV Jan 20 '14 at 16:56

score 1 · Answer 2 · answered Jan 20 '14 at 16:35

We experienced a similar issue with a self-hosted WCF interface which provided a synchronous request/response web service for an asynchronous (2 one way service calls) backend request. Early in our testing, we noticed that after a somewhat variable amount of time, our service became unresponsive to new requests. After some research, we discovered that whenever the backend service (out of our control) did not send a response, we continued to wait indefinitely and as such we kept our client connection open.

We fixed the issue by providing a “time-to-wait” configuration value so we were sure to respond to the client and close the connection. We used something like the following …

Task processTask = Task.Factory.StartNew(() => Process(message));

bool isProcessSuccess = processTask.Wait(shared.ConfigReader.SyncWebServiceWaitTime);

if (!isProcessSuccess)
{ 
 //handle error … 
}

The following link, which provides information regarding WCF Service performance counters, may help further determine if the calls are being closed as expected. http://blogs.microsoft.co.il/blogs/idof/archive/2011/08/11/wcf-scaling-check-your-counters.aspx

Hope this helps.
Regards,

WCF MaxConcurrentSessions exceeded

2 Answers2

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