Just the Facts

• Caching is the system's or the application's ability to save frequently used data to an intermediate storage medium. In ASP.NET, caching comes in two independent but not exclusive flavors: caching application data and caching the output of served pages.

• To cache application data, you use the Cache object, a global container of data with a dictionary-based API and the capabilities of automatically scavenging the memory and getting rid of unused items.

• Items added to the cache can be linked to an array of files and directories as well as to an array of existing cache items, database tables, or external custom events. Whenever files, folders, existing cache items, and database tables are modified, or whenever the external event fires, the item automatically becomes stale and is removed from memory

• Page output caching is the ability to save the raw HTML of a page to a location on the client, the server, or a downstream proxy server. Cached pages can be given a duration and vary in terms of query and form parameters, HTTP headers, and custom strings.

• When the IIS 6.0 process model is enabled, the output caching mechanism is integrated in the Web server. Incoming requests for an ASP.NET page are filtered by a kernel-level driver and examined to see whether they match cached pages.

• By creating user controls, you can cache only a portion of an ASP.NET page.

• In ASP.NET 2.0, new caching features are available, such as post-cache substitution. Post-cache substitution lets you cache the entire page except for a few regions.