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Compile-time conditions in stored proc?
Posted on 2013-06-05
I have some stored procs that reference a few linked servers in a distributed transaction. This works OK in live, but in my DR location I have fewer actual machines, and they contain databases that reside on separate machines in live.
Under the circumstances, i would have to use loop-back linked server names in DR, which would kill the distributed trans, or I would have to have two versions of the code - for DR and Live, that reference actual machine names - which pretty much defeats the purpose of disaster recovery.
I have tried solving the issue by adding conditions like
Is there a way of adding conditional statements that would be evaluated at "prepare" stage?
Or perhaps someone could suggest a different way of achieving what I am after?
Under the circumstances, i would have to use loop-back linked server names in DR, which would kill the distributed trans, or I would have to have two versions of the code - for DR and Live, that reference actual machine names - which pretty much defeats the purpose of disaster recovery.
I have tried solving the issue by adding conditions like
IF @@SERVERNAME = 'SQLPROD1' EXEC SQLPROD2.MyDB.dbo.mySP
ELSE EXEC SQLDR2.MyDB.dbo.mySP
Is there a way of adding conditional statements that would be evaluated at "prepare" stage?
Or perhaps someone could suggest a different way of achieving what I am after?
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5 Comments
The fundamental problem you are facing here is that you are trying to solve applicatively an architecture problem. As a dirty hack you can eventually want to try something like this to fool the compiler (in pseudo code).
For creating linked servers applicatively, you can look at the following link:
http://msdn.microsoft.com/en-us/library/ms190479.aspx
Hope this helps.
if exists( linked server (SQLPROD2) or linked server (SQLDR2))
drop linked server SQLPROD2
drop linked server SQLDR2
IF @@SERVERNAME = 'SQLPROD1'
begin
create linked server SQLPROD2...
EXEC SQLPROD2.MyDB.dbo.mySP
drop linked server SQLPROD2...
end
ELSE
begin
create linked server SQLDR2...
EXEC SQLDR2.MyDB.dbo.mySP
drop linked server SQLDR2...
end
For creating linked servers applicatively, you can look at the following link:
http://msdn.microsoft.com/en-us/library/ms190479.aspx
Hope this helps.
I'm guessing you can get around this by using dynamic SQL:
DECLARE @SQL VARCHAR(max) = NULL;
IF (@@SERVERNAME = 'SQLPROD1')
BEGIN
SET @SQL='EXEC SQLPROD2.MyDB.dbo.mySP';
EXEC @SQL;
END
ELSE
BEGIN
SET @SQL='EXEC SQLDR2.MyDB.dbo.mySP'
EXEC @SQL;
END
<<I'm guessing you can get around this by using dynamic SQL:>>
Definitely a more elegant solution. You just me realize I have a bias onto not mixing up dynamic SQL and multi server distributed transactions for security purposes and error feed backing reasons. Thanks (I do mean it) :)
Definitely a more elegant solution. You just me realize I have a bias onto not mixing up dynamic SQL and multi server distributed transactions for security purposes and error feed backing reasons. Thanks (I do mean it) :)
Both viable ideas, guys. thanks... I have to say that dropping and recreating linked servers sounds a bit clumsy to me, though, and dynamic SQL introduces its own complications because my stored procs have output parameters. Besides, isn't there a performance hit with dynamic SQL because it has to re-generate the execution plan? Or is that a moot point, because SPs (and their execution plans) are atomic, anyway, even when sub-called?
Actually, there is yet another complication to this - I also have a QA environment where server names are yet again different, but there I also have the added complication of database names being different (MyDB_QA1, MyDB_QA2, MyDB_Dev, etc) I do not think that problem can be resolved by architectural changes, as originally pointed out - I have to have these multiple copies of the databases. I guess I will have to go the dynamic SQL route... Thanks again.
Actually, there is yet another complication to this - I also have a QA environment where server names are yet again different, but there I also have the added complication of database names being different (MyDB_QA1, MyDB_QA2, MyDB_Dev, etc) I do not think that problem can be resolved by architectural changes, as originally pointed out - I have to have these multiple copies of the databases. I guess I will have to go the dynamic SQL route... Thanks again.
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