9.1 Caching Opportunities in ASP.NET

ASP.NET provides support for page, partial page, and data caching. Caching a page that is dynamically generated, called page output caching , improves performance by generating the page dynamically only the first time it is accessed. Any subsequent access to the same page will be returned from the cache, saving the time it would have taken to dynamically generate the page. The expiration of a cached page must be explicitly set, after which time the page will be regenerated and recached the next time it is accessed. ASP.NET also supports the ability to cache portions of a page if those portions are encapsulated into a user control.

The other opportunity for performance improvement is to reduce the number of round-trips made to a back-end data server (or even to a local database). Instead of always requesting live data from a data source, you can cache that data in memory and access it locally. Data caching can cause cache coherency problems, but when used correctly, it can dramatically improve application responsiveness. ASP.NET provides a full-featured data cache engine, complete with support for scavenging, expiration, and file and key dependencies. Figure 9-1 shows the two locations where caching can be used to improve performance in ASP.NET applications.

Figure 9-1. Caching Opportunities in ASP.NET