SQL Server Session Management

SQL Server Session Management
Configure SQL Server for ASP.NET SQL Server Session State in Custom Database.
To install the session state database on SQL Server, run Aspnet_regsql.exe tool supply the following information with the command:

aspnet_regsql -ssadd -sstype c -d < Database> -S <Server> -U <Username> -P <Password>

·         The name of the Database, using –d option.
·         The name of the SQL Server instance, using the -S option.
·         The logon credentials for an account that has permission to create a database on a computer running SQL Server. Use the -E option to use the currently logged-on user, or use the -U option to specify a user ID along with the -P option to specify a password.
·         The -ssadd command-line option to add the session state database.
·         The -sstype command-line option to specify the type of session state to use. c for Custom i.e. both session state data and stored procedures are stored in a custom database. The other two types are t- Temporary (i.e. session data is stored in the SQL Server’s tempdb database and stored procedures are installed in the SQL server ASPState database) and p- for Persisted (i.e. both session state data and SPs are stored in the SQL Server ASPState database.)
To run the wizard, run Aspnet_regsql.exe without any command-line arguments, as shown below
aspnet_regsql

Modify the Web.config File of Your Application
To implement ASP.NET SQL Server mode session state management, you must modify the <sessionState> element of your application's Web.config file as follows:
1.       Set the mode attribute of the <sessionState> element to SQLServer to indicate that session state is stored in SQL Server.
2.       Set the sqlConnectionString attribute to specify the connection string for SQL Server. For example:
3.  sqlConnectionString="data source=<Server>; Initial Catalog=<Database>; user id=<Username>; password=<Password>"

The modified <sessionState> element should appear as follows:

<system.web>
   <sessionState     
                    cookieName="s_id"
                    mode="SQLServer"
                    sqlConnectionString="data source=<Server>;Initial Catalog=<Database>;user id=<Username>;password=<Password>"
                    cookieless="false"
                    timeout="20"
    />
<system.web>

Note:
·         “timeout” specifies the number of minutes a session can be idle before it is abandoned. 
·         The user, <Username>, in the ConnectionString, must have permissions to perform this operation on the database.

Important notes:
Some findings related to SQL Server Session Management are as follows:

  •  Make sure SQL Server Agent is started and DeleteExpiredSessions Job exists and is properly scheduled.
  • SessionId is autogenerated (and its value is like “wbdmjp2p0ojzoynnfs40lm4s465b250a”) and its max length is 80 characters.
  • The session id has 24 characters using [a-z] chars and [0-5] digits (total of 32 possible chars which is 2^5) which gives a total of 2^(5*24) = 2^120 possible values. And 8 characters of AppId is also concatenate with 24 characters session id to make a 32 characters application specific sessionid.
  • However, sessionid could be customized by overriding CreateSessionID and Validate methods of SessionIDManager class.
  • If user accesses Expired session, then ASP.Net session management creates new session with the same session id in cookie-ful environment i.e. when cookieless="false".
  • To overcome the above issue, we should use the following code on user logout event
Session.Abandon();
Response.Cookies.Add(new HttpCookie(((System.Web.Configuration.SessionStateSection)ConfigurationManager.GetSection("system.web/sessionState")).CookieName, ""));
·          
Useful Scripts:
--- ASPStateTempApplications table contains Application ID and other info
Select * from ASPStateTempApplications

--- ASPStateTempSessions table contains Session ID and other info
Select * from  ASPStateTempSessions

 --- This select show us the size of each session
SELECT
    a.SessionId,
    SUBSTRING(a.SessionId, 25, 8) AS AppIDHex,
    b.AppId AS AppIDDec,
    b.AppName,
    DATALENGTH(a.SessionItemLong) AS SessionSize_In_Bytes,
    DATALENGTH(a.SessionItemLong)/1000.0 AS SessionSize_In_KBs,
      DATALENGTH(a.SessionItemLong)/1000000.0 AS SessionSize_In_MBs
FROM
    dbo.ASPStateTempSessions AS a
    LEFT OUTER JOIN
    dbo.ASPStateTempApplications AS b
    ON
    SUBSTRING(a.SessionId, 25, 8) =
    SUBSTRING(sys.fn_varbintohexstr(CONVERT(VarBinary,b.AppId)), 3, 8)
WHERE
    --(DATALENGTH(a.SessionItemLong) > 0) And
      b.AppName like '%MyWebApp%'
ORDER BY SessionSize_In_Bytes DESC

 --- This select show us the Total and Avg size of overall MyWebApp sessions
SELECT
  a.AppName,
  SessionCount = COUNT(s.SessionId),
  TotalSessionSize = SUM(DATALENGTH(s.SessionItemLong)),
  AvgSessionSize = AVG(DATALENGTH(s.SessionItemLong))
FROM
  dbo.ASPStateTempSessions AS s
LEFT OUTER JOIN
  dbo.ASPStateTempApplications AS a
  ON SUBSTRING(s.SessionId, 25, 8) = SUBSTRING(sys.fn_varbintohexstr(CONVERT(VARBINARY(8), a.AppId)), 3, 8)
WHERE
      a.AppName like '%MyWebApp%'
GROUP BY a.AppName
ORDER BY TotalSessionSize DESC;

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