Performance Improvement in ASP.NET Using Caching

The challenge in building high-performance, scalable Web applications is the ability to store items, whether data objects, pages, or parts of a page, in memory the initial time they are requested. You can store these items on the Web server or other software in the request stream, such as the proxy server or browser. This allows you to avoid recreating information that satisfied a previous request, particularly information that demands significant processor time or other resources.

ASP.NET provides caching at several levels for you to leverage and improve the responsiveness of your application by storing the page output or application data across HTTP requests and reuse it. This allows the web server to take advantage of processing the request without recreating the information and thus saving time and resources.

Caching Opportunities in ASP.NET web pages

ASP.Net supports both page (or portion of a page) caching and also caching data from a backend data source and storing these individual objects in memory.

To achieve this following features are provided in ASP.NET

• Page output caching
• Page fragment caching
• Data caching

Page Output Caching

Dynamically generated .aspx pages can be cached for efficiency instead of re-generating each .aspx page for identical requests, the pages are cached.

Page Output caching can be achieved in the following 3 ways.

1) This can be achieved by specifying the @OutputCache directive at the top of the ASP.Net page. It controls the caching duration (in seconds).

<%@ OutputCache Duration="3600" VaryByParam="none" %>
<html>
<script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e)
{
msg.Text = DateTime.Now.ToString();
}
</script>
<body>
<h3>Output Cache example</font></h3>
<p>Last generated on: <asp:label id="msg" runat="server"/>
</body>
</html>

2) Programmatically you can achieve this using the HttpCachePolicy sealed class which can be accessed from the HttpResponse.Cache property of the Page.Response property.

HttpCachePolicy class

public sealed class HttpCachePolicy
{
public HttpCacheVaryByHeaders VaryByHeaders {get;}
public HttpCacheVaryByParams VaryByParams {get;}
public void AppendCacheExtension(string extension);
public void SetCacheability(HttpCacheability cacheability);
public void SetExpires(DateTime date);
public void SetLastModified(DateTime date);
public void SetMaxAge(TimeSpan delta);
public void SetNoServerCaching();
public void SetSlidingExpiration(bool slide);
//...
}

Modifying a page's caching policy programmatically.

<html>
<script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e)
{
Response.Cache.SetExpires(DateTime.Now.AddSeconds(360));
Response.Cache.SetCacheability(HttpCacheability.Public);
Response.Cache.SetSlidingExpiration(true);
msg.Text = DateTime.Now.ToString();
}
</script>
<body>
<h3>Output Cache example</font></h3>
<p>Last generated on: <asp:label id="msg" runat="server"/>
</body>
</html>

3) Caching of GET requests with query strings or POST requests with bodies controlled by VaryByParam property. It determines how many versions of the page are cached. Specifying it to "none" means that only GET requests with NO query strings or POST requests with NO body will hit the cache. Specifying VaryByParam to "*" means that as many different querystring or POST body requests are received
will be cached.

The following table gives you a brief idea of the VaryByParam values.