Migrating from ASP to ASP.NET - Caching
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Caching is the process of temporarily storing frequently accessed data to enhance the scalability and performance of a Web application. For example, assume that several news stories located in a database need to be displayed on the homepage of a Web site. Without caching, the database must be queried each time a user hits the page. This causes the database to work harder than it really needs to given that all users share the same data. ASP does contain a basic type of caching exposed through a special kind of state referred to as Application state. Data added into ASP Application state is available to all users visiting the Web application. Although Application state is very useful in a variety of circumstances, it provides no type of automatic expiration for the content being stored. And although ASP.NET still supports Application state, a completely new caching mechanism with automatic content expiration and decay is now available to developers. This allows data caches to automatically expire and be refreshed without forcing the developer to write any code. Data caches can even be linked to files so that a given cache is invalidated and then refreshed when the linked file changes in some manner.
Aside from caching data (such as news headlines), ASP.NET cache objects can also be used to cache entire Web pages or even portions of Web pages, which can greatly enhance a Web site’s scalability and allow database servers to focus on more intensive tasks. This type of functionality can be injected into a page by adding a special page “directive” called OutputCache to the top of the page. A simple OutputCache directive designed to cache an entire ASP.NET page for 60 seconds is shown below:
<%@ OutputCache Duration=”60”
VaryByParam=”none” %>
In cases where only portions of a page need to be cached, this directive can be added into user controls.
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