Pack stuff into a SQL Server binary data type

Question

What can I do wtih a binary data type in SQL Server to make my life easier?

I recently found out about this nifty feature

DECLARE @p0 varbinary(128)
SET @p0 = --?
SET CONTEXT_INFO @p0

How can I in a reasonable efficient manner store data that makes some sense in this binary slot? Oh, and then access that data in some reasonable way?

SELECT ? = context_info
FROM sys.dm_exec_sessions
WHERE session_id = @@SPID

Update: as pointed out by gbn

SELECT ? = CONTEXT_INFO()

A more useful approach would be to rely on CONTEXT_INFO() to return a Row ID of some context table. Say:

SELECT * 
FROM ContextTable 
WHERE RowID = CONTEXT_INFO()

That would allow me to query context information.

Answer 1

It's useful for passing data into a trigger, say, the username from your web site into a audit trigger.

I'd also use CONTEXT_INFO() to read the data back out (for SQL Server 2005 and higher)

One gotcha: it starts NULL but you can not assign NULL back to it after use. You have to use 0x00.