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Publisher3.4 Caching Page Output
Another
new feature of ASP.NET that should not
be overlooked is its support for cachingin particular, output
caching. Output caching provides the ability to have the rendered
output of a page cached for a specified duration simply and easily.
By caching the rendered output in memory, subsequent requests for the
page can be delivered substantially faster and with considerably less
processor utilization than if the page needs to be re-rendered for
each request, which can lead to substantial performance increases.
The ASP.NET team has reported page delivery two to three times faster
when using output caching. Output caching is available for both
ASP.NET pages and ASP.NET user controls.Not every page can be cached in its entirety. Some pages contain too
much dynamic information to be cached as a whole, but even these
pages may have portions that seldom change. By moving these static
portions into user controls (which also provides the possibility of
reuse) and then output caching the user controls, at least some
performance benefit can be realizedeven for very dynamic
pages.The best part about output caching is its simplicity. In its most
basic state, caching the output of a page requires a directive like
the following (which you should add directly below the
@ Page or @
Control directive):
<%@ OutputCache Duration="20" VaryByParam="None" %>
This directive tells ASP.NET to cache the output of the page for 20
seconds and to return the same cached version of the page for all
requests. Example 3-7 demonstrates how to cache the
output of a page for 60 seconds and to cache a different version of
the page for each different value of the name
parameter, when sent as part of the query string of a GET request
(for example,
http://localhost/aspnetian/OutCache.aspx?name=John ).
The cache can be varied by form fields in a POST request as well, if
desired, by setting the value of the
VaryByParam attribute to the name of the form
field to vary by.
Example 3-7. Output caching in ASP.NET
<%@ Page Language="vb" %>
<%@ OutputCache Duration="60" VaryByParam="name" %>
<html>
<head>
<title>Output Cache Demonstration</title>
<script runat="server" >
Sub Page_Load(Sender As Object, e As EventArgs)
lblMessage.Text = "Current time is: " & _
DateTime.Now( )
End Sub
</script>
</head>
<body>
<h1>Demonstration of Output Caching</h1>
<form id="frmPostBack" runat="server">
<asp:label id="lblMessage" runat="server"/>
</form>
</body>
</html>
As explained in Section 3.1.1 earlier in this chapter, you can also have ASP.NET cache
multiple versions of a page on the basis of specific HTTP headers by
using the VaryByHeader attribute, or you can cache
multiple versions of a user control on the basis of some of its
properties by using the VaryByControl attribute.
Caching the output of a user control is essentially the same process
as that shown in Example 3-7, except that you may
not use the VaryByHeader attribute in a user
control.
