How StateServer Session Mode Works?

We used StateServer Session Mode to avoid unnecessary session data loss during restart of web Server. StateServer is maintained by process aspnet_state.exe as a windows Services. This process maintains the all the session data. But need to serialize the data before storing it in StateServer Session Mode. 


As shown in above figure, that client request to the web server, then web server stores the session data on state server. StateServer may be the current system or may be the different system. But it is totally independent of IIS. Destination of StateServer will  depend on the web.config stateConnectionStringattribute settings. If we set it as, It will store data on that local system itself. For change the StateServer destination, we need to change the IP. and make sure, aspnet_state.exe is up and running on that system. other wise you will get the following exception while trying to store data on session.

When we are storing any object on session, that should be serialized. That data will be stored to StateServer system using State Provider. and at the time of retrieving the data, State provider will return the data. The complete flow is given in the below picture.

So based on the above discussion
Advantages : 
  • Its keeps the data separate from IIS so, any Issue with IIS does not hamper Session data.
  • It is useful in web farm and web garden scenarios.
Disadvantages :
  • Process is slow due to Serialization and De-Serialization
  • State Server always need to be up and running.
Now, I am stopping here on StateServer, You will find some more interesting points on Load balancer, Web Farm, Web Garden Section.
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