Output caching is the caching
of pages or portions of pages that are
output to the client. This does not happen automatically. The
developer must enable output caching using either the
OutputCache page directive or the HttpCachePolicy
class. Both methods will be described.
Output caching can be applied to an entire page or a portion of the page. To cache only a portion of a page, the caching is applied to a user control contained within the page. This too will be described later in this section.
directive, like all page
directives, goes at the top of the page file. (For a complete
description of page directives, see Chapter 6.) A
typical example of an
OutputCache page directive
looks something like the following:
<%@ OutputCache Duration="60" VaryByParam="*" %>
The full syntax is:
<%@ OutputCache Duration="number of seconds" VaryByParam="parameter list" Location="location" VaryByControl="control list" VaryByCustom="custom output" VaryByHeader= "header list" %>
Only the first two parameters,
VaryByParam, are required.
VaryBy... parameters allow different versions
of the cached page to be stored, with each version satisfying the
combination of conditions being varied.
The various parameters are described in the following sections.
specifies the number of seconds that the page or user control is cached. Items placed in the output cache are only valid for this specified time ...