使用SQL Server存储ASP.NET Session变量
创建和配置ASP.NET Session状态数据库
在基于NLB（网络负载平衡）环境下的ASP.NET Web应用程序开发，我们需要将Session存储在数据库中供多个Web应用程序调用，以下为配置方法及注意事项。
1.创建用于存储ASP.NET Session的数据库（远程、本地皆可，使用数据库用户身份认证） 在Windows\Microsoft.NET\Framework/V2.0.50727目录下使用如下命令： aspnet_regsql.exe -S <SQL Server IP> -U <User Name> -P <Password> -E -ssadd -sstype c -d <Database Name> 命令执行后就会成功建立起用于存储ASP.NET Session变量的数据库了。
2.Web.Config文件配置项 我们需要在ASP.NET Web应用程序中的Web.Config文件修改sessionState配置项以使Session状态数据库生效。 配置节点如下： <sessionState mode="SQLServer" sqlConnectionString="server=<Server IP>;database=<Database Name>;uid=<User Name>;pwd=<Password>;" allowCustomSqlDatabase="True" cookieless="false" timeout="20" />
3.注意在进行系统测试（主要是负载测试）的时候，因为数据库访问负载的增加，需要调整SQL Server相应超时的配置项以适应负载。（默认值为10，请适度进行调整。）
ASP.NET Session状态数据库数据模型 1.ASPStateTempSessions表定义
| 列名 | 类型 | 描述 |
|---|---|---|
| SessionId | nvarchar(88) | Session ID + application ID |
| Created | datetime | Date and time session was created (UTC) |
| Expires | datetime | Date and time session expires (UTC) |
| LockDate | datetime | UTC date and time session was locked |
| LockDateLocal | datetime | Local date and time session was locked |
| LockCookie | int | Lock ID |
| Timeout | int | Session timeout in minutes |
| Locked | bit | 1=Session locked, 0=Session not locked |
| SessionItemShort | varbinary(7000) | Serialized session state (if <= 7,000 bytes) |
| SessionItemLong | image | Serialized session state (if > 7,000 bytes) |
| Flags | int | Session state flags (1=Uninitialized session) |
| 列名 | 类型 | 描述 |
|---|---|---|
| AppId | int | Application ID |
| AppName | char(280) | Application name |
3.使用的存储过程
| Stored Procedure | Description |
|---|---|
| CreateTempTables | Creates the ASPStateTempSessions and ASPStateTempApplications tables; called during setup, but not called by SqlSessionStateStore. |
| DeleteExpiredSessions | Used by SQL Server Agent to remove expired sessions. |
| GetHashCode | Hashes an application name and returns the hash; called by TempGetAppID. |
| GetMajorVersion | Returns SQL Server's major version number. |
| TempGetAppID | Converts an application name into an application ID; queries the ASPStateTempApplications table and inserts a new record if necessary. |
| TempGetStateItem | Retrieves read-only session state from the database (ASP.NET 1.0; ASP.NET 1.1/SQL Server 7). |
| TempGetStateItem2 | Retrieves read-only session state from the database (ASP.NET 1.1). |
| TempGetStateItem3 | Retrieves read-only session state from the database (ASP.NET 2.0). |
| TempGetStateItemExclusive | Retrieves read/write session state from the database (ASP.NET 1.0; ASP.NET 1.1/SQL Server 7). |
| TempGetStateItemExclusive2 | Retrieves read/write session state from the database (ASP.NET 1.1). |
| TempGetStateItemExclusive3 | Retrieves read/write session state from the database (ASP.NET 2.0). |
| TempGetVersion | Marker whose presence indicates to ASP.NET 2.0 that the session state database is ASP.NET 2.0-compatible. |
| TempInsertStateItemLong | Adds a new session, whose size is > 7,000 bytes, to the database. |
| TempInsertStateItemShort | Adds a new session, whose size is <= 7,000 bytes, to the database. |
| TempInsertUninitializedItem | Adds a new uninitialized session to the database in support of cookieless sessions. |
| TempReleaseStateItemExclusive | Releases a lock on a session; called when ASP.NET determines that a request has timed out and calls the provider's ReleaseItemExclusive method. |
| TempRemoveStateItem | Removes a session from the database when the session is abandoned. |
| TempResetTimeout | Resets a session's timeout by writing the current date and time to the corresponding record's Expires field. |
| TempUpdateStateItemLong | Updates a session whose size is > 7,000 bytes. |
| TempUpdateStateItemLongNullShort | Updates a session whose old size is <= 7,000 bytes, but whose new size is > 7,000 bytes. |
| TempUpdateStateItemShort | Updates a session whose size is <= 7,000 bytes. |
| TempUpdateStateItemShortNullLong | Updates a session whose old size is > 7,000 bytes, but whose new size is <= 7,000 bytes. |
ASP.NET 状态数据库FAQ
1.如果把SESSION值存放到数据库中去，用户关闭了程序那怎么样清空数据库里的SESSION值呢？ 实际ASP.NET在创建状态数据库的时候会在SQL Server代理（SQL Server Agent）的作业中添加一个作业，名称为<状态数据库名>_Job_DeleteExpiredSessions。如果打开SQL Server代理服务数据库可以通过添加的状态记录的超时时间字段（Exprires）定期对超时的状态数据进行删除。
2.ASPStateTempSessions表中的SessionId字段如何使用？ 数据库中此表的SessionID字段的值，由SessionID和AppID共同组成，最后8位为AppID所以，后8位之前一定是SessionID。例如，存储在数据库中的值为"ekr30c3mwvnc3145yrswew3a037e5e5a"，后8位的"037e5e5a"为AppID，而前面的"ekr30c3mwvnc3145yrswew3a"为应用程序中你可以使用Session.SessionID获得的字符串。
3.如何判断Session何时被更新的？ Session记录被更新时会同时更新Expires和LockDateLocal，Expires字段为UTC时间，如果想通过本地之间进行比较判断还是需要使用LockDateLocal。
4.获得Web.config配置文件节点信息的程序？
''获得Web.config文件配置实例Dim configuration As System.Configuration.Configuration = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("~/web.config")''获得状态配置节点实例Dim mSessionStateSection As System.Web.Configuration.SessionStateSection =CType(configuration.GetSection("system.web/sessionState"),System.Web.Configuration.SessionStateSection)
''获得状态模式Response.Write(mSessionStateSection.Mode) ''获得状态超时时间Response.Write(mSessionStateSection.Timeout)
