Introduction
Through this article am just focusing on the basics of caching and how did caching come into picture. This article is targeted to the beginners.
Caching is...
a technique used to temporarily store the frequently used data and Web pages on the main memory, to be reused later on.
Since it minimizes the usage of server resources, the performance of the application using this technique increases.
Why caching?
Retrieving data from a database is one of the slowest Web site operations.
Every time the page requests for data, it has to go through "client->server->database->server->client" cycle, which is very time consuming. Time taken might increase as per the data density and in turn affect the performance.
It will be more pathetic when multiple users access a Web site simultaneously. Now this is where "caching" comes into picture.
So if the database data is cached in memory and database-access with every page request is avoided, the performance of your application increases.
Different types of caching:
ASP.Net provides three basic types of caching:
- Page level output caching
- Fragment caching
- Data Caching
Page level output caching:
Page caching is mainly used for static pages, where the contents does not change. Output caching has the advantage of being incredibly simple to implement, and are sufficient in many cases.
This technique caches the output of a page so that content of pages are not generated every time it is loaded. Output caching simply keeps a copy of the HTML that was sent in response to a request in memory. In this case the subsequent requests are severed with the cached out until cache expires. This gives a great performance increase of web application.
Just add the OutputCache directive to the page you wish to cache.
for eg. <%@ OutputCache Duration="30" VaryByParam="none" %>
Code snippet:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Sample.aspx.cs" Inherits="Sample" %>
<%@ OutputCache Duration="10" VaryByParam="none"%>
Date time:
<% DateTime t = DateTime.Now;
Response.Write(t.ToString()); %>
This page is cached for 10 seconds. When this page was last cached the date/time was 1/1/2009 11:27:27 AM. When you refresh repeatedly this time remains constant until the cache is expired, then it is updated to the current time. So after 10 seconds, you can get the current time. This is because, ASP.Net caches the HTML using Output Caching.
Page Fragment Caching:
This type of technique is used when we need to cache only a part(or rather Fragment) of page instead of the whole page. Suppose, if we need to cache only header of a page, then instead of caching the whole page, its better to cache only header.
When you login to a website, you might find your name on the header. This happens with all the users. So header has to be stored in cache till he logs out. So the header has to be an user control. Fragment caching is applied to this user control.
Just add the OutputCache directive to the user control page you wish to cache.
for eg. <%@ OutputCache Duration="30" VaryByControl="Header1" %>
This will cache Header1 for 30 seconds
Data Caching:
Data caching is also called Application caching. It is much more powerful than the other two caching options. It caches data as objects and its scope is as that of the application. Here, an item is cached under a name , then extract it with the same name when required. Data caching is done using "cache" class.
Data caching is done in this way:
Cache["ID"] = EmployeeID;
Here EmployeeID is cached under "ID" key.
Now while extracting,
EmployeeID = Cache["ID"];
Where does cached data gets stored?
The location for cached data can be specified in OutputCache directive.
- Any - This stores the output cache in the client's browser, on the proxy server (or any other server) that participates in the request, or on the server where the request is processed. By default, Any is selected.
- Client Caching - This stores output cache in the client's browser.
- Downstream - This stores the output cache in any cache-capable devices that participate in the request. To store the output cache on any HTTP 1.1 cache-capable devices including the proxy servers and the client that made request.
- Web Server Caching - This stores the output cache on the Web server.
- None - Output caching is deactivated.