What happens when application pool re-cycles in ASP.NET MVC?

Question

I was using Session heavily for storing data of posted requests from client side on server. On research, various answers over stackoverflow pointing me , Not to use Session in ASP.NET MVC. Main reason is : Application Pool recycles frequently during life time of production server and this causes Session to recycle as well.

Thatswhy I am thinking to replace session objects with de-serialize able string "....". My whole concern is : This singleton object containing this string (de-serialize able into Objects ) must not corrupt/recycle or re-initialize on app pool re-cycle.

So my final question would be : What happens on app pool-recycle? Only Session re-cycles ? Or the whole memory re-cycles and re-initializes?

My target web server : Microsoft ASP.NET with MVC

Answer 1

When the application recycles, the windows process the site is running in w3wp.exe ends and a new one is created. It's also possible a site has multiple worker processes for one application pool. In that case they all end and 1 spins up, and new worker processes will be created as they are needed.

When this happens, anything the website code was storing in memory is lost. This includes In Process Session information.

However .Net Session State can work in two modes, in process, or database. You can run the aspnet_regsql tool to create a database in sql server for storing session information. Then you can change the web.config to have session run in the database. You can use the same session apis, they work the same in both modes. But putting it in database mode causes it to persist everything to the database instead of in process memory. Then when AppPool recycles, you lose nothing.

RegSql Doc: https://msdn.microsoft.com/library/ms229862(v=vs.100).aspx

A well designed ASP.Net Site (be it MVC, Web Forms, WebApi(1/2)) etc. should be designed to be able to fully recover from any recycles. A site recycle should not break your web site.

Answer 2

Recycling the Application Pool will blow away your AppDomain and everything in it, including all static values.

This is why it loses session state in the first place.

You probably want a database.

Answer 3

SLaks pretty much answered your question. Here is the solution -

In ASP.Net MVC, we do not use Session State like Web Form.

However, you can still use Session State, but you want to use external Session State provider instead of default InProc mode - values and variables are stored in memory on the local Web server.

You have few options -

• StateServer
• SQLServer
• Custom mode using Redis Cache like Azure .