How to log when a function is called?

Denis Gobo — Thu, 08 May 2008 17:25:00 GMT

This question came up today and here is one way of doing it. It requires running xp_cmdshell so this is probably not such a good idea.
The problem with functions is that you cannot just insert into any table. INSERT, UPDATE, and DELETE statements modifying table variables local to the function.
EXECUTE statements calling an extended stored procedures are allowed.
So with this in mind we know that we can call xp_cmdshell, from xp_cmdshell we can use osql
Let's take a look
We will be using tempdb

--Create the table
USE tempdb
go
CREATE TABLE LogMeNow (SomeValue varchar(50), SomeDate datetime default getdate())
go

--Here is the proc
CREATE PROC prLog
@SomeValue varchar(50)
AS
INSERT LogMeNow (SomeValue) VALUES(@SomeValue)
go

--And here is the function
CREATE FUNCTION fnBla(@id int)
RETURNS int
AS
BEGIN
DECLARE @SQL varchar(500)
SELECT @SQL = 'osql -S' +@@servername +' -E -q "exec tempdb..prLog ''fnBla''"'
EXEC master..xp_cmdshell @SQL
RETURN @id
END

Now call the function a couple of times

SELECT dbo.fnBla(1)
SELECT dbo.fnBla(2)
SELECT dbo.fnBla(4)

And look inside the table

SELECT * FROM LogMeNow

What if you were to run this?

SELECT dbo.fnBla(4),* FROM sys.sysobjects

See the problem? The function will be called for every row, if you have a big table this can be problematic!!!!!!!!

I tested this on SQL 2000 and on SQL 2005(including a named instance). So there you have it, this is one way. does it smell kludgy and do I feel somewhat dirty now? yes it does indeed :-(

Denis Gobo : logging

How to log when a function is called?