What is the difference between in-proc and out-of-proc session state in IIS?

When it comes to managing session state in Internet Information Services (IIS), there are two primary modes: in-proc and out-of-proc.

In-Proc Session State

In-proc session state means that the session data is stored within the memory of the IIS process itself. This allows for fast access to session data since it's all contained within the same process. However, this also means that if the IIS process restarts or crashes, all session data is lost.

Out-of-Proc Session State

Out-of-proc session state involves storing session data outside of the IIS process, such as in a separate process, a database, or a shared server. While this provides resilience in case of IIS process failures, accessing session data may be slower compared to in-proc session state due to the overhead of communication between processes.

Key Differences:

• In-proc session state stores data within the IIS process, while out-of-proc stores data externally.
• In-proc session state offers faster access but is prone to data loss on IIS restarts or crashes.
• Out-of-proc session state provides resilience but may have slower access times due to inter-process communication.

Choosing between in-proc and out-of-proc session state depends on the specific requirements of the application in terms of performance, scalability, and data persistence.