ASP.NET - Directives - Output Cache

In ASP.NET, the Output Cache directive is used to improve the performance of a web application by caching the output generated by a page or a user control. When an ASP.NET page or control is requested, the server first checks whether the output is already cached. If it is, the server returns the cached output instead of regenerating the output from scratch. This can significantly reduce the page load time and improve the scalability of the application.

The syntax of the Output Cache directive is as follows:

<%@ OutputCache Duration="time" VaryByParam="parameter(s)" %>

Here are some examples of how to use the Output Cache directive:

Caching a page for a specific duration:

<%@ OutputCache Duration="60" %>

This will cache the output of the page for 60 seconds. If the page is requested again within 60 seconds, the cached output will be returned.

Caching a page based on query string parameters:

<%@ OutputCache Duration="60" VaryByParam="id" %>

This will cache the output of the page based on the value of the "id" query string parameter. If the same "id" value is requested again within 60 seconds, the cached output will be returned.

Caching a page based on multiple query string parameters:

<%@ OutputCache Duration="60" VaryByParam="id;name" %>

This will cache the output of the page based on the values of the "id" and "name" query string parameters. If the same "id" and "name" values are requested again within 60 seconds, the cached output will be returned.

Caching a user control:

<%@ OutputCache Duration="60" VaryByControl="MyUserControl" %>

This will cache the output of the "MyUserControl" user control for 60 seconds. If the user control is requested again within 60 seconds, the cached output will be returned.

Caching a page based on the user's identity:

<%@ OutputCache Duration="60" VaryByCustom="user" %>

This will cache the output of the page based on the user's identity. If a user with the same identity requests the page again within 60 seconds, the cached output will be returned.