State Management Techniques in asp.net

Generally web application depends on stateless Http protocol for user requests.

But http protocol can’t retain the information about user requests. In typical client and server communication using HTTP protocol, page is created each time the page is requested.

We have state management techniques to maintain state for the Http protocol; we have two types of state managements like client side and server side.

Client Side State management

ASP.NET provides various client side state management options like Cookies, Query Strings (URL), Hidden fields, View State and Control state.

Cookie:

A cookie is a small piece of text stored on user's computer. Usually, information is stored as name-value pairs. Cookies are used by websites to keep track of visitors. Every time a user visits a website, cookies are retrieved from user machine and help identify the user. 

Hidden Fields 

Hidden fields are used to store data at the page level. As its name says, these fields are not rendered by the browser. It's just like a standard control for which you can set its properties. Whenever a page is submitted to server, hidden fields values are also posted to server along with other controls on the page

View State:
View State can be used to store state information for a single user. View State is a built in feature in web controls to persist data between page post backs. You can set View State on/off for each control using EnableViewState property. By default, EnableViewState property will be set to true. View state mechanism poses performance overhead. View state information of all the controls on the page will be submitted to server on each post back. To reduce performance penalty, disable View State for all the controls for which you don't need state. (Data grid usually doesn't need to maintain state). You can also disable View State for the entire page by adding EnableViewState=false to @page directive. 


Query strings:
 
Query strings are usually used to send information from one page to another page. They are passed along with URL in clear text

Control State:


Control state can be used to store critical, private information across post backs. Control state is another type of state container reserved for controls to maintain their core behavioral functionality whereas View State only contains state to maintain control's contents (UI).

Server Side State management:
 
State information will be maintained on the server. Application, Session, Cache and Database are different mechanisms for storing state on the server. 



Application object:



Application object is used to store data which is visible across entire application and shared across multiple user sessions. Data which needs to be persisted for entire life of application should be stored in application object.
In classic ASP, application object is used to store connection strings. It's a great place to store data which changes infrequently. We should write to application variable only in application_Onstart event (global.asax) or application.lock event to avoid data conflicts. Below code sample gives idea 

Session object:
 
Session object is used to store state specific information per client basis. It is specific to particular user. Session data persists for the duration of user session you can store session's data on web server in different ways. Session state can be configured using the <session State> section in the application's web.config file.  

Configuration information:
<sessionState mode = <"inproc" | "sqlserver" | "stateserver">
 cookieless = <"true" | "false">
 timeout = <positive integer indicating the session timeout in minutes>
 sqlconnectionstring = <SQL connection string that is only used in the SQLServer mode>
 server = <The server name that is only required when the mode is State Server>
 port = <The port number that is only required when the mode is State Server>      
You can disable session for a page using EnableSessionState attribute. You can set off session for entire application by setting mode=off in web.config file to reduce overhead for the entire application.
Session state in ASP.NET can be configured in different ways based on various parameters including scalability, maintainability and availability

• In process mode (in-memory)- State information is stored in memory of web server
• Out-of-process mode- session state is held in a process called aspnet_state.exe that runs as a windows service.
• Database mode session state is maintained on a SQL Server database.

Finally selecting between client side and server side state management is based on application Requirement and resources. Both have their own advantages and disadvantages.

For more information 

http://msdn.microsoft.com/en-us/library/75x4ha6s.aspx

Beginning ASP.NET 4: in C# and VB (Wrox Programmer to Programmer)