what is difference between session, cache and profile in asp.net

Question

You use cache typically when you want to improve site performance: reduce database calls, accessing files on filesystem, calling external services, etc.

Scenario 1: Assume there is an application which has a page that lists all products stored in database. Users have need in product list filtering feature (like on ebay or amazon for example). Also it is known that list of products and product features are changing rarely comparing to frequency of product list page usage.

Solution 1: Here you can use cache to reduce database calls. You put product list and product features to cache to perform filtering in memory and avoid redundant database calls. Cache should be invalidated whenever product list or feature changes. This solution should be OK until memory consumption handling is cheaper than gain in performance.

As a good resource I suggest reading the ASP.NET Caching: Techniques and Best Practices MSDN article.

In profile you typically save data which is specific to concrete user and should be available at every time user logs into system.

Scenario 2: Consider you have the same application as in Scenario 1 but now you need to provide ability for users to save their filter preferences (kind of list of favourite filters).

Solution 2: You can create a kind of filter-state class and store it in user profile. As a result users will not be bothered in specifying filter parameters again and again and these preferences would be available every time user logs in.

Session is used to store user-specific information that could be accessible from all web pages and will not be needed on next time user logs in.

Scenario 3: Assume there is some e-commerce application and marketing people want to see what is happening on site in close real time manner, i.e. see what pages were visited by certain users while they were logged in. Consider this scenario as a selected users activity snapshot.

Solution 3: Here you can use session to log what URLs were visited by users and then generate report for marketing people.

As for state management you can also reffer to another MSDN article ASP.NET State Management Overview.

Another good answer which highlights the difference between objects that are managing asp.net application state.

Hope this helped you a bit.