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Can a clustered index solve a SQL Server deadlock?
At some time or another every DBA has been faced with the challenge of solving a deadlock issue in their SQL Server database. In the following tip we will look at how indexes and more specifically clustered indexes on the right columns can help reduce the chance of your applications receiving this dreaded error:
Why are there so many deadlocks in Eclipse?
We’re seeing many deadlocks, where different sessions are running the exact same delete query (generated by Eclipse LINQ) from the same host:
Why do I get a deadlock on the DELETE statement?
I get a deadlock when a SQL Server Job runs. The deadlock occurs on a simple DELETE statement. I would have thought there would have to be a SELECT/UPDATE query running to cause the deadlock? But looks like it is DELETE/DELETE deadlock… What I am looking for is why I am getting a DELETE/DELETE deadlock.
When to use clustered index in SQL Server?
Testing with your application/database should be done to ensure that you are getting the best performance possible. Ensure all your tables have a clustered index. Check out the SQL Server Tables without a Clustered Index tip for useful queries to diagnose the issue in your SQL Server databases.
How is indexing used to prevent deadlocks?
So by adding a covering index we can avoid our session getting blocked and prevent the deadlock from occurring. Just to prove that the scan is the cause of the block, we can add FORCESCAN to our query and see what happens. So now we can see that we’re once again scanning the index and now we’re back to the blocking situation.
What does clustered index scan in SQL mean?
A clustered index scan. So what that means is that SQL is scanning the clustered index from top to bottom until it hits the locked row. It can’t go any further at that point so ends up getting blocked.
What does it mean when index gets blocked in SQL?
So what that means is that SQL is scanning the clustered index from top to bottom until it hits the locked row. It can’t go any further at that point so ends up getting blocked.
When do you create a unique nonclustered index?
When you create a UNIQUE constraint, a unique nonclustered index is created to enforce a UNIQUE constraint by default. You can specify a unique clustered index if a clustered index on the table does not already exist.
Why is my new index not getting blocked?
WOW, no deadlock! So what’s happening now. Let’s think about the update first, now be aware that because we’ve added an index, our update as also got to update that index too. Because of that, we’ll now see a lock on the new index as well. But why is our SELECT not getting blocked? Let’s have a look at that execution plan now…