We are thinking of using HttpRuntime.Cache for storing data accessed frequently by all users, but wanted to know what are the performance implications of using HttpRuntime.Cache? Are the contents of the cache transported in every http request and response? How much information can be reasonably stored in there?
What are the performance implications of using HttpRuntime.Cache?
Normally, Cache is stored in server's memory, unless server are configured as Web Farm or Web Garden. As the result, accessing to Cache is really fast compare is Database.
Are the contents of the cache transported in every http request and response?
No.
How much information can be reasonably stored in there?
Virtually, there is no limit. However, you only want to cache the information - you often needed and do not change very often. In addition, you do not want to cache images and files - Cache is not meant for that.