Output Caching in MVC

Introduction

The main purpose of using Output Caching is to dramatically improve the performance of an ASP.NET MVC Application. It enables us to cache the content returned by any controller method so that the same content does not need to be generated each time the same controller method is invoked. Output Caching has huge advantages, such as it reduces server round trips, reduces database server round trips, reduces network traffic etc.

Keep the following in mind:-

• Avoid caching contents that are unique per user.
• Avoid caching contents that are accessed rarely.
• Use caching for contents that are accessed frequently.
• Let's take an example. My MVC application displays a list of database records on the view page so by default each time the user invokes the controller method to see records, the application loops through the entire process and executes the database query. And this can actually decrease the application performance. So, we can advantage of the "Output Caching" that avoids executing database queries each time the user invokes the controller method. Here the view page is retrieved from the cache instead of invoking the controller method and doing redundant work.

Cached Content Locations

In the above paragraph I said, in Output Caching the view page is retrieved from the cache, so where is the content cached/stored?

Please note, there is no guarantee that content will be cached for the amount of time that we specify. When memory resources become low, the cache starts evicting content automatically.

OutputCache label has a "Location" attribute and it is fully controllable. Its default value is "Any", however there are the following locations available; as of now, we can use any one.

1. Any   2. Client   3. Downstream   4. Server   5. None   6. ServerAndClient

With "Any", the output cache is stored on the server where the request was processed. The recommended store cache is always on the server very carefully. You will learn about some security related tips in the following "Don't use Output Cache".

Output Cache Filter

The OutputCache filter allow you to cache the data that is output of an action method. By default, this attribute filter cache the data till 60 seconds. After 60 sec, Asp.Net MVC will execute the action method again and cache the output again.

Enabling Output Caching

You can enable the output caching for an action method or controller by adding an [OutputCache] attribute as shown below:

[OutputCache(Duration=20, VaryByParam="none")]

public ActionResult Index()

{

 ViewBag.Message = DateTime.Now.ToString();

 return View();

}

The output of the Index() action method will be cached for 20 seconds. If you will not defined the duration, it will cached it for by default cache duration 60 sec. You can see the cache effect by applying the break point on index method as shown below.

Output Caching Location

By default, content is cached in three locations: the web server, any proxy servers, and the user's browser. You can control the content's cached location by changing the location parameter of the OutputCache attribute to any of the following values: Any, Client,Downstream, Server, None, or ServerAndClient.

By default, the location parameter has the value Any which is appropriate for most the scenarios. But some times there are scenarios when you required more control over the cached data.

Suppose you want to cache the logged in use information then you should cached the data on client browser since this data is specific to a user. If you will cached this data on the server, all the user will see the same information that is wrong.

You should cache the data on the server which is common to all the users and is sensitive.

Configure Cache Location

For configuring the cache location, you need to add the System.Web.UI namespace on your controller. You can cached the user's personal information in his browser like as below.

[OutputCache(Duration = 7200, Location = OutputCacheLocation.Client, VaryByParam = "none", NoStore = true)]

public ActionResult Index()

{

 ViewBag.Message = "Welcome : " + User.Identity.Name;

 return View();

}