Losing Session State

I have an ASP.net application where Users aren't able to successfully complete certain actions, for reasons, I'm assuming, can only be related to losing their session (which is where I maintain their current user information, and how determine whether they are logged in)

I'm at a loss as to why they would lose their session, so my first question is:

What (in general) would cause a user to lose their session in ASP.net?

and since I don't know when a user loses their session and can't reproduce it myself:

How can I track when I user loses their session

Below is my sessionState config for reference

<sessionState
           mode="InProc"
           cookieless="false"
           cookieName="My.Site.Com"
           timeout="480"/>

A number of things can cause session state to mysteriously disappear.

1. Your sessionState timeout has expired
2. You update your web.config or other file type that causes your AppDomain to recycle
3. Your AppPool in IIS recycles
4. You update your site with a lot of files, and ASP.NET proactively destroys your AppDomain to recompile and preserve memory.

If you are using IIS 7 or 7.5, here are a few things to look for:

1. By default, IIS sets AppPools to turn themselves off after a period of inactivity.
2. By default, IIS sets AppPools to recycle every 1740 minutes (obviously depending on your root configuration, but that's the default)
3. In IIS, check out the "Advanced Settings" of your AppPool. In there is a property called "Idle Time-out". Set that to zero or to a higher number than the default (20).
4. In IIS, check the "Recycling" settings of your AppPool. Here you can enable or disable your AppPool from recycling. The 2nd page of the wizard is a way to log to the Event Log each type of AppPool shut down.

If you are using IIS 6, the same settings apply (for the most part but with different ways of getting to them), however getting them to log the recycles is more of a pain. Here is a link to a way to get IIS 6 to log AppPool recycle events:

http://web.archive.org/web/20100803114054/http://surrealization.com/sample-code/getnotifiedwhenapppoolrecycles/

If you are updating files on your web app, you should expect all session to be lost. That's just the nature of the beast. However, you might not expect it to happen multiple times. If you update 15 or more files (aspx, dll, etc), there is a likelyhood that you will have multiple restarts over a period of time as these pages are recompiled by users accessing the site. See these two links:

http://support.microsoft.com/kb/319947

http://msdn.microsoft.com/en-us/library/system.web.configuration.compilationsection.numrecompilesbeforeapprestart.aspx

Setting the numCompilesBeforeAppRestart to a higher number (or manually bouncing your AppPool) will eliminate this issue.

You can always handle Application_SessionStart and Application_SessionEnd to be notified when a session is created or ended. The HttpSessionState class also has an IsNewSession property you can check on any page request to determine if a new session is created for the active user.

Finally, if it's possible in your circumstance, I have used the SQL Server session mode with good success. It's not recommended if you are storing a large amount of data in it (every request loads and saves the full amount of data from SQL Server) and it can be a pain if you are putting custom objects in it (as they have to be serializable), but it has helped me in a shared hosting scenario where I couldn't configure my AppPool to not recycle couple hours. In my case, I stored limited information and it had no adverse performance effect. Add to this the fact that an existing user will reuse their SessionID by default and my users never noticed the fact that their in-memory Session was dropped by an AppPool recycle because all their state was stored in SQL Server.

I was having a situation in ASP.NET 4.0 where my session would be reset on every page request (and my SESSION_START code would run on each page request). This didn't happen to every user for every session, but it usually happened, and when it did, it would happen on each page request.

My web.config sessionState tag had the same setting as the one mentioned above.

cookieless="false"

When I changed it to the following...

cookieless="UseCookies"

... the problem seemed to go away. Apparently true|false were old choices from ASP.NET 1. Starting in ASP.Net 2.0, the enumerated choices started being available. I guess these options were deprecated. The "false" value has never presented a problem in the past - I've only noticed in on ASP.NET 4.0. I don't know if something has changed in 4.0 that no longer supports it correctly.

Also, I just found this out not long ago. Since the problem was intermittent before, I suppose I could still encounter it, but so far it's working with this new setting.

Your session is lost becoz....

I have found a scenario where session is lost - In a asp.net page, for a amount text box field has invalid characters, and followed by a session variable retrieval for other purpose.After posting the invalid number parsing through Convert.ToInt32 or double raises a first chance exception, but error does not show at that line, Instead of that, Session being null because of unhandled exception, shows error at session retrieval, thus deceiving the debugging...

HINT: Test your system to fail it- DESTRUCTIVE.. enter enough junk in unrelated scenarios for ex: after search results shown enter junk in search criteria and goto details of search result... , you would be able to reproduce this machine on your local code base too...:)

Hope it Helps, hydtechie

In my case setting AppPool->AdvancedSettings->Maximum Worker Proccesses to 1 helped.

You could add some logging to the Global.asax in Session_Start and Application_Start to track what's going on with the user's Session and the Application as a whole.

Also, watch out of you're running in Web Farm mode (multiple IIS threads defined in the application pool) or load balancing because the user can end up hitting a different server that does not have the same memory. If this is the case, you can switch the Session mode to SQL Server.

I was only losing the session which was not a string or integer but a datarow. Putting the data in a serializable object and saving that into the session worked for me.

Had a problem on IIS 8 when retrieving Content via Ajax. The issue was that MaximumWorkerProcesses was set to 2 and Javascript opened 17 concurrent requests. That was more than the AppPool could handle and a new pool (without auth-data) was opened.

Solution was to Change MaximumWorkerProcesses to 0 in IIS -> Server -> Application Pools -> [myPool] -> Advanced Settings -> Process Model -> MaximumWorkerProcesses.

Dont know is it related to your problem or not BUT Windows 2008 Server R2 or SP2 has changed its IIS settings, which leads to issue in session persistence. By default, it manages separate session variable for HTTP and HTTPS. When variables are set in HTTPS, these will be available only on HTTPS pages whenever switched.

To solve the issue, there is IIS setting. In IIS Manager, open up the ASP properties, expand Session Properties, and change New ID On Secure Connection to False.

I had same problem by losing sessions. every time , every page reload, my sessions clear and by new reload any page, my sessions returned by valid value...

i fixed it by change MaximumWorkerProcesses from 0 to 1 in iis

I was struggling with this issue for 14 days.

Here's what helped me:

1. Check your recycling options in App Pool > Advanced settings. Turn off all of the options so it won't recycle on its own.
2. Check your web.config file for the executionTimeout property under httpRuntime and increase its value.
3. Check your web.config file for the timeout property under sessionState and increase its value (I set it to 300 minutes).
4. Go to the server's event log and check the Application log for unhandled exceptions that may cause the worker process to crash. Fix them in your code or use try and catch to eliminate this crash.
5. Try changing the value of your maximum worker process from 0 to 1 or the other way around, this may also solve this issue.

In my case, session state was loosing due to Load Balancer. Session was storing in one server and Load balancer was redirecting next call to another server where session state was missing.