binary_str

Is a binary constant, or a constant that is implicitly convertible to binary, to associate with the current session or connection.

@ binary_var

Is a varbinary or binary variable holding a context value to associate with the current session or connection.

The preferred way to retrieve the context information for the current session is to use the CONTEXT_INFO function. Session context information is also stored in the context_info columns in the following system views:

• sys.dm_exec_requests
  
• sys.dm_exec_sessions
  
• sys.sysprocesses
  

SET CONTEXT_INFO cannot be specified in a user-defined function. You cannot supply a null value to SET CONTEXT_INFO because the views holding the values do not allow for null values.

SET CONTEXT_INFO does not accept expressions other than constants or variable names. To set the context information to the result of a function call, you must first include the result of the function call in a binary or varbinary variable.

When you issue SET CONTEXT_INFO in a stored procedure or trigger, unlike in other SET statements, the new value set for the context information persists after the stored procedure or trigger is completed.

A. Setting context information by using a constant

SET CONTEXT_INFO 0x01010101
GO
SELECT context_info 
FROM sys.dm_exec_sessions
WHERE session_id = @@SPID;
GO

B. Setting context information by using a function

DECLARE @BinVar varbinary(128)
SET @BinVar = CAST(REPLICATE( 0x20, 128 ) AS varbinary(128) )
SET CONTEXT_INFO @BinVar

SELECT CONTEXT_INFO() AS MyContextInfo;
GO

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