Caching in .NET

Caching is a technique of application performance improvement by storing frequently used data/information in memory, so that, when the same data/information is needed next time, it could be retrieved from the memory instead of being generated by the application.

This information get stored in web server, any proxy servers, or web browser, depending on type of caching and configuration.

ASP.NET provides following different types of caching:

1. Output Caching: Output cache stores a copy of the finally rendered HTML pages or part of pages sent to the client. When the next client requests for this page, instead of regenerating the page, a cached copy of the page is sent, thus saving time. 

By default, when you use the [OutputCache] attribute, content is cached in three locations: the web server, any proxy servers, and the web browser. You can control exactly where content is cached by modifying the Location property. By default, the Location property has the value Any, It can be changes to Client, Downstream, Server, none, ServerAndClient.

[OutputCache] attribute includes a Location property set to the value OutputCacheLocation. Also includes a NoStore property. The NoStore property is used to inform proxy servers and browser that they should not store a permanent copy of the cached content.

Asp.NET Example:-

<%@ OutputCache Duration="15" Location="Client"  VaryByParam="None" NoStore=" true" %>

MVC Example:-

[OutputCache(Duration=3600, VaryByParam="none", Location=OutputCacheLocation.Client, NoStore=true)]

VaryByParam: - This property enables you to create different cached versions of the very same content when a form parameter or query string parameter varies. When different values of the Id parameter are passed to the controller action, different cached versions of the Details view are generated.

The OutputCache directive has the following attributes, which helps in controlling the behaviour of the output cache:

Attribute	Values	Description
DiskCacheable	true/false	Specifies that output could be written to a disk based cache.
NoStore	true/false	Specifies that should or not store a permanent copy of the cached content.
CacheProfile	String	Name of a cache profile as to be stored in web.config.
VaryByParam	None,*,Param	Semicolon delimited list of string specifies query string values in a GET request or variable in a POST request.
VaryByHeader	*,Header	Semicolon delimited list of strings specifies headers that might be submitted by a client.
VaryByCustom	Browser,Custom string	Tells ASP.NET to vary the output cache by browser name and version or by a custom string.
Location	Any, Client, Downstream, Server, None	Define cache storing location.
Duration	Number	Number of seconds the page or control is cached.

2. Data Caching: It caching data from a data source. As long as the cache is not expired, a request for the data will be fulfilled from the cache. When the cache is expired, data is obtained by the data source and the cache is refilled.

To implement set the EnableCaching attribute of the data source control to be 'true' and set the Cacheduration attribute. It will implement caching and the cache will expire defined seconds. The timestamp changes with every refresh, but if you change the data in the table within defined seconds, it is not shown before the cache expires.

3. Object Caching: Object caching is caching the objects on a page, such as data-bound controls. The cached data is stored in server memory. This will offer more flexibility while caching.

Example:-

Cache["key"] = item;

OR

Cache.Insert("item", obj, null, DateTime.MaxValue, TimeSpan.FromMinutes(10));

Inserts an item into the cache with the key name, value, expiration policy, expiration policy and other details 

4. Class Caching: Web pages or web services are compiled into a page class in the assembly, when run for the first time. Then the assembly is cached in the server. Next time when a request is made for the page or service, the cached assembly is referred to. When the source code is changed, the CLR recompiles the assembly.

5. Configuration Caching: Application wide configuration information is stored in a configuration file. Configuration caching stores the configuration information in the server memory.