Caching in ASP.net

Caching

Introduction: It is a way to store the frequently used data into the server memory which can be retrieved very quickly. And so provides both scalability and performance. For example if user is required to fetch the same data from database frequently then the resultant data can be stored into the server memory and later retrieved in very less time (better performance). And the same time the application can serve more page request in the same time (scalability).

Drawback: Suppose the server memory is filled with the data then the remaining part of the data is stored into the disk which slower the complete system performance. That's why self limiting caching techniques are best; where once the server memory gets filled the data has been selectively removed from the server memory to ensure that the application performance is not degraded.

Caching Types: Basically, caching is of two types:

1. Output caching - The rendered html page is stored into the cache before sending it to the client. Now, if the same page is requested by some other client the already rendered htm page is retrieved from the server memory and sent to the client, which saves the time requires rendering and processing the complete page.
2. Data Caching - The important pieces of information, that are time consuming and frequently requested, are stored into the cache. For example a data set retrieved from the database. It is very similar to application state but it is more server friendly as the data gets removed once the cache is filled.

There are two more models which are built on the above two types: 

1. Fragment caching - Instead of caching the complete page, some portion of the rendered html page is cached. E.g.: User Control used into the page is cached and so it doesn't get loaded every time the page is rendered. 
2. Data Source Caching - It is caching built into the data source controls (eg. XmlDataSource, sqlDataSource etc). It is very similar to data caching but here the caching is not handled explicitly but the data source control manages it as per the settings made on the data controls. 

this is from http://wiki.asp.net/page.aspx/655/caching-in-aspnet/