Execution Characteristics of Extended Stored Procedures

The execution of an extended stored procedure has these characteristics:

• The extended stored procedure function is executed under the security context of Microsoft® SQL Server™.
• The extended stored procedure function runs in the process space of SQL Server.
• The Microsoft Win32® thread associated with the execution of the extended stored procedure is the same one used for the client connection.

After the extended stored procedure DLL is loaded, the DLL remains loaded in the address space of the server until the SQL Server is stopped or the administrator explicitly unloads the DLL by using  DBCC DLL_name (FREE). This is the default behavior.

The extended stored procedure can be executed from Transact-SQL as a stored procedure by using the EXECUTE statement:

EXECUTE @retval = xp_extendedProcName @param1, @param2 OUTPUT

where

@retval

Is a return value.

@param1

Is an input parameter.

@param2

Is an input/output parameter.

Caution Extended stored procedures offer performance enhancements and extend SQL Server functionality. However, because the extended stored procedure DLL and SQL Server share the same address space, a problem procedure can adversely affect SQL Server functioning. Although exceptions thrown by the extended stored procedure DLL are handled by SQL Server, it is possible to damage SQL Server data areas. As a security precaution, only SQL Server system administrators can add extended stored procedures to SQL Server. These procedures should be thoroughly tested before they are installed.