In ASP.NET there are three types of methods for session maintenance :
Session State Service
Microsoft SQL Server
In the in-process storage mode the session state is stored in the memory space of the Asp.net_wp.exe process. No doubt, it is the fastest method but the performance will be affected due to the consumption of the bulk memory on the web server.
Session state service is an another method and can be used as an alternative to in-process storage method. In this method the serialized session information is stored in a separate process (Asp.net_state.exe). Also, the cost of serialization can affect the performance bulk of objects are stored at a time.
Lastly, the third method which is known as Microsoft SQL Server is used to store state information.In this mode the serialized session information is stored in the MS SQL Server database. And similar to session state service in this also the performance will be affected due to storing of bulk objects