Applying constraints to a large table

Alyanto
Alyanto used Ask the Experts™
on
I Have had to rebuild a database for a customer and whilst most of this process has worked well I have come up against a problem.  On three tables when I run code similar to that below:

IF NOT EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N'[FK_GroupUserMap_User]') AND parent_object_id = OBJECT_ID(N'[GroupUserMap]'))
ALTER TABLE [GroupUserMap]  WITH NOCHECK ADD  CONSTRAINT [FK_GroupUserMap_User] FOREIGN KEY([UserInfoKey])
REFERENCES [UserInfo] ([UserInfoKey])

Open in new window


It is taking an inordinate amount of time to do 6 million rows.  Is there a way top improve this performance?

The SQL SERVER 2012 installation is on a virtual server which I have no administrative rights to and the customer has fairly limited IT resources too.
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Olaf DoschkeSoftware Developer

Commented:
Why? The existence of the foreign key is not checked for 6 million rows but only a few rows of metadata in sys.foreign_keys and since your alter table adds a constraint with NOCHECK, this shouldn't take long, as it doesn't check the 6 million rows.

If anything does take long, then it's not this code but something else you don't show here.

Bye, Olaf.

Author

Commented:
Hey Olaf
That was my thoughts, but there is nothing else in the script that affects this code just more of the same.  and yet it runs for a weekend and no completion :(   I have pretty much read around the subject as completely is I think possible  I am hoping someone else has had a similar problem and found a solution.
Olaf DoschkeSoftware Developer

Commented:
Sure, you don't end with something like ALTER TABLE table WITH CHECK CHECK CONSTRAINT ALL?
I still stand to this, a constraint added with NOCHECK does not check rows, so the size of the table will not matter. You need to look for something else.

Bye, Olaf.
Ensure you’re charging the right price for your IT

Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden using our free interactive tool and use it to determine the right price for your IT services. Start calculating Now!

Author

Commented:
No Olaf I highlighted the code as written and execute it and I agree with you, I was hoping for someone to have had this experience and found a way around it.  That may never happen, I just need to give this a fair amount of time before I decide what to do next.
There must be a lock involved. I recommend you to install Adam Machanic's sp_whoisactive stored procedure and while you run that ALTER statement in a separate query window you will execute :

EXEC sp_whoisactive

and check for the blocking_session_id column. If there is a session_id in that column in the row that shows your ALTER statement then you will have to kill/terminate that process.

Here is the procedcure:

http://sqlblog.com/blogs/adam_machanic/archive/2012/03/22/released-who-is-active-v11-11.aspx

Download here: http://sqlblog.com/files/folders/beta/entry42453.aspx

It is free.
Vitor MontalvãoIT Engineer
Distinguished Expert 2017

Commented:
A lock should be a good explanation but what make a table to be locked for a full weekend?
Do you have any job running? Something like an Import/Export or even a maintenance job scheduled for weekends?

Also if you don't want to use sp_WhoIsActive you can use the built in sp_who2 and check for the rows with blocked column <> 0.

Author

Commented:
Well hats off to you,  Adam Mechanic tool soon found out that a user was simply ignoring the administrators instruction to cease and desist use.  Many thanks for the Cluedo tool.

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial