Insight Caching

Note: All this data has been copied from various sources for the purpose of knowledge sharing. Data content  can be either as it is or with little modification.
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Introduction: Caching enables you to store data in memory for rapid access. When the data is accessed again, applications can get the data from the cache instead of retrieving it from the original source. This can improve performance and scalability. In addition, caching makes data available when the data source is temporarily unavailable.Larger number of client means larger number of requests to your web server and heavy load on the network causing performance issue. For solving this problem, I worked on using caching on our web application.

What is Caching? 
 web site can have a heavy load on the site which can increase exponentially, which can slow down the server as well as the access of the site. Slow access is the most common problem for web sites when accessed by a large number of clients simultaneously. For resolving this problem, we can use a high level of hardware configuration, load balancer, high bandwidth, but load is not the only reason that makes a website slow, so we need to provide a kind of mechanism which will also provide fast data access and provide performance improvements. Caching provides the solution.Caching is a technique where we can store frequently used data, and web pages are stored temporarily on the local hard disk for later retrieval. This technique improves the access time when multiple users access a web site simultaneously, or a single user accesses a web site multiple times. Caching for web applications can occur on the client (browser caching), on a server between the client and the web server, (proxy caching / reverse proxy caching), and on the web server itself (page caching or data caching).

Thus in total we have three type of caching 
1)Browser caching --  Caching for web applications can occur on the client.
2) Proxy caching/ reverse proxy caching -- on a server between the client and the web server.
3) Page caching/ data caching -- on the web server itself.

1. Client Caching: In Client Caching, the client browser performs caching by storing cached data on the local disk as a temporary file or in the browser internal memory. This provides quick access of some information which reduces the network load and the server load also. This information can't be shared by other clients so it is client specific.

2. Proxy Caching: The main disadvantage of client caching is data that is stored on the client browser is client specific. Proxy caching uses a dedicated server that stores caching information in between the client and the web server in a shared location so that all clients can use the same shared data. The proxy server (e.g., Microsoft Proxy Server) fulfills all the requests for the web page without sending out the request to the actual web server over the internet, resulting in faster access.

Proxy caches are often located near network gateways to reduce bandwidth usage. Some times multiple proxy cache servers are used for larger number of clients. This is called a cache array.

4. Web Server Caching: In web server caching, cached data is stored inside the web server. Data caching and pagecaching uses the web sever caching mechanism.

Advantages of Caching

1) reduced network traffic

2) Reduces bandwidth consumption.

3) Reduces server overload.

4) Reduces time take to download information. 

5) Can also used to reduced round trips to database server. 

Caching in .NET

ASP.NET provides support for page, partial page (fragment), and data caching.

ASP.NET supports three types of caching:

1. Page output caching [Output caching]
2. Fragment caching [Output caching]
3. Data caching

Now whatever we are getting, if there is some page which changes frequently, JIT needs to compile it every time. We can use page output caching for those pages whose content is relatively static. So rather than generate a page on each user request, we can cache the page using page output caching so that it can be accessed from the cache itself. Pages can be generated once and then cached for subsequent fetches. Page output caching allows the entire content of a given page to be stored in the cache.

In the picture, when the first request is generated, the page is cached and for the same page request in future, the page is retrieved from the cache rather that regenerating the page.

For output caching, an OutputCache directive can be added to any ASP.NET page, specifying the duration (in seconds) that the page should be cached.

Output caching location

As I have already mentioned, we can store cached data in different locations like client, server, or in between the client and the server. Now I am going to discuss how to set the location of cached data. If we store cached data, it saves the page rendering time by fetching data from the cache. There is another way that we can save cached data on the client browser, which reduces network traffic. The OutputCache directive on a page enables all three types of caching—server, client, and proxy—by default.

2. Page Fragment Caching

<!— UserControl.ascx —>

<%@ OutputCache Duration='60'

                VaryByParam='none' %>

<%@ Control Language="'C#'" %>

<script runat="server">

  protected void Page_Load(Object src, EventArgs e)

  {

     _date.Text = "User control generated at " +

                   DateTime.Now.ToString();

  }

</script>

<asp:Label id='_date' runat="'server'" />

Here I have user caching on a user control, so whenever we use it in a page, part of the page will be cached.

3. Data Caching: Caching data can dramatically improve the performance of an application by reducing database contention and round-trips. Simply, data caching stores the required data in cache so that the web server will not send requests to the DB server every time for each and every request, which increases web site performance. For datacaching, we need to cache data which is accessible to all or which is very common. The data cache is a full-featured cache engine that enables you to store and retrieve data between multiple HTTP requests and multiple sessions within the same application.

Now let us see how we can implement data caching in our web application. There are three different ways to add data or objects into cache. But based on the situation, we have to access it differently. These methods are Cache[],Cache.add(), cache.insert(). The following table will show you the clear difference of the there methods.