State Management in ASP.NET

By Santosh Kumar Jun 15, 2011
Understanding State Management and Session Object in ASP.NET

State Management in ASP.NET:

State management is the process by which you maintain state and page information over multiple requests for the same or different pages.

There are 2 types State Management:

 

  1. Client – Side State Management
    This stores information on the client's computer by embedding the information into a Web page, a uniform resource locator(url), or a cookie. The techniques available to store the state information at the client end are listed down below:

    a. View State – Asp.Net uses View State to track the values in the Controls. You can add custom values to the view state. It is used by the Asp.net page framework to automatically save the values of the page and of each control just prior to rendering to the page. When the page is posted, one of the first tasks performed by page processing is to restore view state.

    b. Control State – If you create a custom control that requires view state to work properly, you should use control state to ensure other developers don't break your control by disabling view state.

    c. Hidden fields – Like view state, hidden fields store data in an HTML form without displaying it in the user's browser. The data is available only when the form is processed.

    d. Cookies – Cookies store a value in the user's browser that the browser sends with every page request to the same server. Cookies are the best way to store state data that must be available for multiple Web pages on a web site.

    e. Query Strings - Query strings store values in the URL that are visible to the user. Use query strings when you want a user to be able to e-mail or instant message state data with a URL.

    2. Server – Side State Management
    a. Application State - Application State information is available to all pages, regardless of which user requests a page.

    b. Session State – Session State information is available to all pages opened by a user during a single visit.

    Both application state and session state information is lost when the application restarts. To persist user data between application restarts, you can store it using profile properties.

 

Client Side State Management:

ViewState:


The ViewState property provides a dictionary object for retaining values between multiple requests for the same page. When an ASP.NET page is processed, the current state of the page and controls is hashed into a string and saved in the page as a hidden field. If the data is too long for a single field, then ASP.NET performs view state chunking (new in ASP.NET) to split it across multiple hidden fields. The following code sample demonstrates how view state adds data as a hidden form within a Web page's HTML:

<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE” value="/wEPDwUKMTIxNDIyOTM0Mg9kFgICAw9kFgICAQ8PFgIeBFRleHQFEzQvNS8yMDA2IDE6Mzc6MTEgUE1kZGROWHn/rt75XF/pMGnqjqHlH66cdw==" />



Encrypting of the View State: You can enable view state encryption to make it more difficult for attackers and malicious users to directly read view state information. Though this adds processing overhead to the Web server, it supports in storing confidential information in view state. To configure view state encryption for an application does the following:

<Configuration>
         <system.web> 
                <pages viewStateEncryptionMode="Always"/> 
          </system.web> 
</configuration>



Alternatively, you can enable view state encryption for a specific page by setting the value in the page directive, as the following sample demonstrates:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" ViewStateEncryptionMode="Always"%> 


View State is enabled by default, but if you can disable it by setting the EnableViewState property for each web control to false. This reduces the server processing time and decreases page size.
Reading and Writing Custom View State Data:
If you have a value that you'd like to keep track of while the user is visiting a single ASP.NET Web page, adding a custom value to ViewState is the most efficient and secure way to do that. However, ViewState is lost if the user visits a different Web page, so it is useful only for temporarily storing values.
Example: Determine the time of last visit to the page

// Check if View State object exists, and display it if it does
If (ViewState ["lastVisit"]!= null) 
Label1.Text = (string)ViewState["lastVisit"]; else 
Label1.Text = "lastVisit ViewState not defined."; 
// Define the ViewState object for the next page view ViewState.Add("lastVisit", DateTime.Now.ToString()); 



Control State: If you create a custom control that requires ViewState, you can use the ControlState property to store state information for your control. ControlState allows you to persist property information that is specific to a control and cannot be turned off like the ViewState property. To use control state in a custom control, your control must override the OnInit method and call the Register-RequiresControlState method during initialization and then override the SaveControl-State and LoadControlState methods.

Hidden fields: ViewState stores information in the Web page using hidden fields. Hidden fields are sent back to the server when the user submits a form; however, the information is never displayed by the Web browser (unless the user chooses to view the page source). ASP.NET allows you to create your own custom hidden fields and store values that are submitted with other form data. A HiddenField control stores a single variable in its Value property and must be explicitly added to the page. You can use hidden fields only to store information for a single page, so it is not useful for storing session data. If you use hidden fields, you must submit your pages to the server using Hypertext Transfer Protocol (HTTP) POST (which happens if the user presses a button) rather than requesting the page using HTTP GET (which happens if the user clicks a link). Unlike view state data, hidden fields have no built-in compression, encryption, hashing, or chunking, so users can view or modify data stored in hidden fields.

Cookies: Web applications can store small pieces of data in the client's Web browser by using cookies. A cookie is a small amount of data that is stored either in a text file on the client file system (if the cookie is persistent) or in memory in the client browser session (if the cookie is temporary). The most common use of cookies is to identify a single user as he or she visits multiple Web pages.

Reading and Writing Cookies:
A Web application creates a cookie by sending it to the client as a header in an HTTP response. The Web browser then submits the same cookie to the server with every new request.
Create a cookie -> add a value to the Response.Cookies HttpCookieCollection.
Read a cookie -> read values in Request.Cookies.
Example:

// Check if cookie exists, and display it if it does 
if (Request.Cookies["lastVisit"] != null) // Encode the cookie in case the cookie contains client-side script Label1.Text = Server.HtmlEncode(Request.Cookies["lastVisit"].Value);
else Label1.Text = "No value defined";
// Define the cookie for the next visit Response.Cookies["lastVisit"].Value = DateTime.Now.ToString();Response.Cookies["lastVisit"].Expires = DateTime.Now.AddDays(1);



If you do not define the Expires property, the browser stores it in memory and the cookie is lost if the user closes his or her browser.

To delete a cookie, overwrite the cookie and set an expiration date in the past. You can't directly delete cookies because they are stored on the client's computer.
Controlling the Cookie Scope: By default, browsers won't send a cookie to a Web site with a different hostname. You can control a cookie's scope to either limit the scope to a specific folder on the Web server or expand the scope to any server in a domain. To limit the scope of a cookie to a folder, set the Path property, as the following example demonstrates:

Example:

Response.Cookies["lastVisit"].Path = "/Application1"; 



Through this the scope is limited to the “/Application1” folder that is the browser submits the cookie to any page with in this folder and not to pages in other folders even if the folder is in the same server. We can expand the scope to a particular domain using the following statement:
Example:
Response.Cookies[“lastVisit”].Domain = “Contoso”;

Storing Multiple Values in a Cookie:
Though it depends on the browser, you typically can't store more than 20 cookies per site, and each cookie can be a maximum of 4 KB in length. To work around the 20-cookie limit, you can store multiple values in a cookie, as the following code demonstrates:
Example:

Response.Cookies["info"]["visit"].Value = DateTime.Now.ToString();
Response.Cookies["info"]["firstName"].Value = "Tony";
Response.Cookies["info"]["border"].Value = "blue";
Response.Cookies["info"].Expires = DateTime.Now.AddDays(1);



Running the code in this example sends a cookie with the following value to the Web browser:
(visit=4/5/2006 2:35:18 PM) (firstName=Tony) (border=blue)

Query Strings: Query strings are commonly used to store variables that identify specific pages, such as search terms or page numbers. A query string is information that is appended to the end of a page URL. A typical query string might look like the following real-world example:
http://support.microsoft.com/Default.aspx?kbid=315233
In this example, the URL identifies the Default.aspx page. The query string (which starts with a question mark [?]) contains a single parameter named “kbid,” and a value for that parameter, “315233.” Query strings can also have multiple parameters, such as the following real-world URL, which specifies a language and query when searching the Microsoft.com Web site:
http://search.microsoft.com/results.aspx?mkt=en-US&setlang=en-US&q=hello+world

Value Name | ASP.NET Object | Value
mkt | Request.QueryString[“mkt”] | en-US
setlang | Request.QueryString[“setlang”] | en-US
q | Request.QueryString[“q”] | hello world

Limitations for Query Strings:
1. Some Browsers and client devices impose a 2083 – character limit on the length of the URL.
2. You must submit the page using an HTTP GET command in order for query string values to be available during page processing. Therefore, you shouldn't add query strings to button targets in forms.
3. You must manually add query string values to every hyperlink that the user might click.
Example:

Label1.Text = "User: " + Server.HtmlEncode(Request.QueryString["user"]) + 
", Prefs: " + Server.HtmlEncode(Request.QueryString["prefs"]) +
", Page: " + Server.HtmlEncode(Request.QueryString["page"]);



Server - Side State Management:

Application State: ASP.NET allows you to save values using application state, a global storage mechanism that is accessible from all pages in the Web application. Application state is stored in the Application key/value dictionary. Once you add your application-specific information to application state, the server manages it, and it is never exposed to the client. Application state is a great place to store information that is not user-specific. By storing it in the application state, all pages can access data from a single location in memory, rather than keeping separate copies of the data. Data stored in the Application object is not permanent and is lost any time the application is restarted.

ASP.NET provides three events that enable you to initialize Application variables (free resources when the application shuts down) and respond to Application errors:

a. Application_Start: Raised when the application starts. This is the perfect place to initialize Application variables.

b. Application_End: Raised when an application shuts down. Use this to free application resources and perform logging.

c. Application_Error: Raised when an unhandled error occurs. Use this to perform error logging.


Session State: ASP.NET allows you to save values using session state, a storage mechanism that is accessible from all pages requested by a single Web browser session. Therefore, you can use session state to store user-specific information. Session state is similar to application state, except that it is scoped to the current browser session. If different users are using your application, each user session has a different session state. In addition, if a user leaves your application and then returns later after the session timeout period, session state information is lost and a new session is created for the user. Session state is stored in the Session key/value dictionary.

You can use session state to accomplish the following tasks:
i. Uniquely identify browser or client-device requests and map them to individual session instances on the server. This allows you to track which pages a user saw on your site during a specific visit.

ii. Store session-specific data on the server for use across multiple browser or client-device requests during the same session. This is perfect for storing shopping cart information.

iii. Raise appropriate session management events. In addition, you can write application code leveraging these events.

ASP.NET session state supports several different storage options for session data:

a. InProc Stores session state in memory on the Web server. This is the default, and it offers much better performance than using the ASP.NET state service or storing state information in a database server. InProc is fine for simple applications, but robust applications that use multiple Web servers or must persist session data between application restarts should use State Server or SQLServer.

b. StateServer Stores session state in a service called the ASP.NET State Service. This ensures that session state is preserved if the Web application is restarted and also makes session state available to multiple Web servers in a Web farm. ASP.NET State Service is included with any computer set up to run ASP.NET Web applications; however, the service is set up to start manually by default. Therefore, when configuring the ASP.NET State Service, you must set the startup type to Automatic.

c. SQLServer Stores session state in a SQL Server database. This ensures that session state is preserved if the Web application is restarted and also makes session state available to multiple Web servers in a Web farm. On the same hardware, the ASP.NET State Service outperforms SQLServer. However, a SQL Server database offers more robust data integrity and reporting capabilities.

d. Custom Enables you to specify a custom storage provider. You also need to implement the custom storage provider.

e. Off Disables session state. You should disable session state if you are not using it to improve performance.

 

Advantages:


Advantages of Client – Side State Management:

1. Better Scalability: With server-side state management, each client that connects to the Web server consumes memory on the Web server. If a Web site has hundreds or thousands of simultaneous users, the memory consumed by storing state management information can become a limiting factor. Pushing this burden to the clients removes that potential bottleneck.

2. Supports multiple Web servers: With client-side state management, you can distribute incoming requests across multiple Web servers with no changes to your application because the client provides all the information the Web server needs to process the request. With server-side state management, if a client switches servers in the middle of the session, the new server does not necessarily have access to the client's state information. You can use multiple servers with server-side state management, but you need either intelligent load-balancing (to always forward requests from a client to the same server) or centralized state management (where state is stored in a central database that all Web servers access).

Advantages of Server – Side State Management:

1. Better security: Client-side state management information can be captured (either in transit or while it is stored on the client) or maliciously modified. Therefore, you should never use client-side state management to store confidential information, such as a password, authorization level, or authentication status.

2. Reduced bandwidth: If you store large amounts of state management information, sending that information back and forth to the client can increase bandwidth utilization and page load times, potentially increasing your costs and reducing scalability. The increased bandwidth usage affects mobile clients most of all, because they often have very slow connections. Instead, you should store large amounts of state management data (say, more than 1 KB) on the server.

 

 

Understanding Session Object in ASP.NET

 

In classic ASP, the Session object was held in process (as was everything) to the IIS process and therefore any crash to the IIS or apps pool being reset will cause the whole Session object being resettled. Hence this will make the Session objects not reliable at all and cannot be used to stored important data especially if your website is dealing with client login information or e-commerce type of website. In ASP.NET, new features have been introduced to make the Session objects more reliable and robust.

Main Contents


There are three types of storage providers for ASP.NET as opposed to 1 provider in classic ASP Session object.
1. In Process Session State store (Stores sessions in ASP.NET memory cache--> Used in Classic ASP)
2. State Server Session State Store (Stores sessions in the ASP.NET State Server service).
3. Sql Session State Store (Stores sessions in Microsoft SQL Server Database and is configured with aspnet_regsql.exe).

To change the different provider of session state, you need to edit your web.config file.
<configuration>
<system.web>
<sessionState mode="Off|Inproc|StateServer|SQLServer|Custom"/>
</system.web>
</configuration>

InProcess Session State


InProc Session Model is the fastest,common and the default Session provider in ASP.NET. In proc Session State is what you normally use in Classic ASP. The Session key and data is stored inside the memory and therefore it is the fastest among all the session objects provider.  It has significant limitations on the reliability. If the worker process or application domain recycles, all the session state data is lost.
ASP.NET application may restart for number of reasons.

1. Changing and Editing web.config or Global.asax file.
2. Modified files in the \bin or App_Code directory.
3. The process model of the web.config or machine.config file indicating when the application should be 
    restart.
4. Application pool in IIS being recycled(either manually or scheduled).
5. Cannot be used on WebFarm

The conclusion, In Process Session State works great for smaller applications that require only single Web server (consists of single processor) and your website doesn't store or rely heavily on session data.

Note:
If your web server consists of multiple processor and you have assigned your current worker process to be on multiple processor (You can set this option under your application pool Web garden settings), then you must not use In process Session State cause you will be losing Session state everytime the request is redirected to another processor.

Code Samples for Storing Data in Session objects

1. Storing String in Session Objects
    Session["MyData"] = TextBox1.Text;

2. Storing Objects in Session Objects
    Client oClient = new Client();
    Session["MyData"] = oClient;

Code Samples for Retrieving Data in Session Objects
1. Retrieving String in Session Objects.
    TextBox1.Text = Session["MyData"].ToString();
 

2. Retrieving Objects in Session Objects
    Client oClient = (Client)Session["MyData"];

State Server Session State


Out of Process Session State is held in a process called aspnet_state.exe that runs as Windows Service. You need to start the service manually from the ServiceManager. This is because the state service is not started by default. To start the service manually, open the Service Manager and find Server called ASP.NET state Service.
or to run it manually from command line
    net start aspnet_state

By default the State Service listens on port 42424 but this port can be changed at the registry key.
The Key is in
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\aspnet_State\Parameters\Port

Edit your web.config files and changes the InProc to State Server as the code shown below
<configuration>
<system.web>
<sessionState mode="StateServer" stateConnectionString="tcpip=127.0.0.1:42424"/>
</system.web>
</configuration>

Note :
You could run the StateServer on your own local web server or on another machine separately. If you run the StateService on another machine, make sure that the port is open. You can check if the port is opened easily by running telnet command. 
E.g telnet 192.168.6.1 42424 
If you got the reply from telnet, it means the port is open.

Because your application's code runs in the ASP.NET Worker Process and the StateService runs on separate Worker Process, object stored in the Session can't be stored as references. Your objects must be marked by [Serializable] attribute. Only classes that marked with the [Serializable] attribute can be serialized.

Sample Code


[Serializable]
public class Person {
public string firstName;public string lastName;public override string ToString() 
{
return firstName + " " + lastName;
}
}

After you have marked the class as serializable, then you can stored the objects in the Session variables
e.g
Person oPerson = new Person();
Session["MyData"] = oPerson;

For world class,highly available and scalable Website, consider using Session model other than in Proc. Even you can guarantee via your load balancing appliance that your session will be sticky , you still have applicatio recycling issues to contend with. The Out of Proc State Service data is persisted across application pool recycles but not computer reboots. However if your state service is stored on a different machine entirely, it will survive Web Server recycles and reboots.

SQL Session State


This is the last part of the Session State store that I am going to discuss. As you seen from above article, Session can be stored in memory and State Server. The last part would be storing the Session State in SQL Server.  InProc State Server offers speed, State Server offers resilience and speed balance while storing Sessions in SQL Server will offer reliability that can serve your sessions to a very  large web farm that can survive from IIS restarts or State Server restarts.

Before you can start using SQL to store your session state, you need to do few steps below to set up your database.

ASP.NET provide a very handy and useful tools to help you configure the database. You need to use
aspnet_regsql.exe in your command prompt. The utility is located on C:\Windows\Microsoft.Net\Framework\<version>.
If you type aspnet_regsql in the command prompt, it will launch the GUI version of the aspnet tools, You cannot use it for configuring the database to store the Session.

Type the command line below to configure the database for Session support.
aspnet_regsql.exe -S localhost -U sa - P worldofasp -ssadd -sstype c -d dbName

Three options exists for -sstype (t,p or c)
The most significant differences is that the
-ssytpe t option does not persist session state data across SQL Server restarts whereas the-sstype p option does.
In the example above,we use option -sstype c , so that you can specify custom database name to store your Session. If you use -sstype t or p then your Session database will be stored on default databasename called ASPState

Next step would be changing the connection string in
web.config
<sessionState mode="SQLServer" sqlConnectionString="data source=127.0.0.1;
userid=sa;password=worldofasp;database=dbName"
/>


Storing Objects in SQL Store would be the same as storing objects in State Server. All the objects need to be marked as Serializable. You can check the Session values in your database after all the database has been created.
Before you decide which Session Store you are going to use in your websites, You need to analyze the requirements and how important session data to your website. If your site is running on very large web farm and you need extremely robust and reliable Session objects, then SQL Session Store will be the perfect one cause it can survive from IIS restarts, Server restarts or SQL server restarts.  But the bottleneck would be on the performance of your SQL Server machine. You need to have a very fast and reliable SQL Server cause every session data will be retrieved from your Database.

 

 

 

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