Session State Modes

Storage location

InProc - session kept as live objects in web server (aspnet_wp.exe)

StateServer - session serialized and stored in memory in a separate process aspnet_state.exe). State Server can run on another machine

SQLServer - session serialized and stored in SQL server


Performance

InProc - Fastest, but the more session data, the more memory is consumed on the web server, and that can affect performance.

StateServer - When storing data of basic types (e.g. string, integer, etc), in one test environment it's 15% slower than InProc. However, the cost of serialization/deserialization can affect performance if you're storing lots of objects. You have to do performance testing for your own scenario.

SQLServer - When storing data of basic types (e.g. string, integer, etc), in one test environment it's 25% slower than InProc. Same warning about serialization as in StateServer.