July 15, 2015 at 11:36 am
I am fairly new to SQL. I had a query that executed in about 20 seconds pulling from database 1. The only changes I made were to make it pull from database 2. It is currently running and has been for over an hour and a half. I am at a loss for why this happened. Any ideas are very much appreciated.
Thank you
July 15, 2015 at 12:51 pm
There are many possible reasons for this including:
1. Much more data in the table(s) being accessed in database2
2. Database2 being on a different server and not having as many resources
3. Statistics not being accurate in database2 so the optimizer isn't choosing an optimal plan
4. Index differences between databases
5. A cached plan for the query in database2 that is not optimal for the parameters provided.
There are probably others I've missed. The first thing I'd check the following:
1. The row counts in each database
2. The estimated execution plans for the query in each database to see what the optimizer is doing differently
Jack Corbett
Consultant - Straight Path Solutions
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July 16, 2015 at 1:22 pm
It would help to know what query you are running. Is database2 on the same SQL Server or a linked server to another server.
Have stats been updated on both tables/databases recently? How large of tables are both of these?
Can you do a query plan for this query to see where it is performing most of its time? Are there any scans going on?
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