Sql-server – SQL Server Linked Server RPC Options

In the SQLOS a scheduler is created for each logical processor that SQL Server sees. With hyperthreading enabled this equates to double the schedulers. One of the purposes for the SQLOS is to minimize and prevent context switching from occuring which is why only one scheduler is created for each logical processor. Once the SQLOS creates the schedulers, the total number of workers is divided amongst the schedulers. The SQLOS implements a form of cooperative scheduling in that the workers yield the scheduler as it requires unavailable resources, or reaches its execution quantum allowing other workers to execute on the scheduler. This keeps context switching to a minimum since the scheduler is doing the work and they are bound one for one.

Understanding that background, hyperthreading somewhat works opposite of how SQLOS is specifically designed to function. Specifically, parallelism can be problematic with hyperthreading and can result in high CXPACKET waits since SQLOS may try to run a query at DOP 8 on what is reality a DOP 4 system. If your CPU utilization is low, you might not notice, but the higher your CPU utilization goes the more problematic it could become. I recently had a discussion on twitter regarding this, and the consensus was "It Depends" as to whether or not it would help or hurt.

If you have a lot of signal waits on your server, but you have low CPU utilization, you may see benefit enabling hyperthreading which will double your internal schedulers and spread the workers out more which means they won't wait to execute in the runnable queue as long. However if your workload utilized parallelism heavily you get heavy CXPACKET waits in sys.dm_os_wait_stats, you might look at disabling hyperthreading to see if it reduces your waits.

From My understanding of this issue it's a "HOP" issue.

i.e. you are trying to use server A to relay your login details (with SSPI) to Server B.

In SQL Server 2005 they have added a whole load of security issues that make this harder than it should be. The words "Kerberos Authentication" will become the bain of most sys-admins/DBA's lives. It effectively is used for pass-through authentication.

Here are the basics of what you need. 1) The servers (A and B) need to be set-up in Active Directory(AD) with delegation for Kerberos enabled. (this is set through your active directory admin panel)

2) The service account that your SQL Servers run under need to have delegation enabled also (this is also set through your active directory admin panel). - if they are not running under a service account, you need to create one.

3) The Servers need to have SPN's defined for the instance and the HOST and the machine name. (Using a tool called SetSPN in the windows support tools)

Support Tools (SetSPN is in this set) http://www.microsoft.com/downloads/details.aspx?FamilyID=96a35011-fd83-419d-939b-9a772ea2df90&DisplayLang=en

(Overview of how to add an SPN) http://technet.microsoft.com/en-us/library/bb735885.aspx

4) You may need to set your DB to "trustworthy"

ALTER DATABASE SET trustworthy on

5) After you have all of this done restart your instances.

6) Then try create your linked server again.

Finally you can test your connection to SQL Server. This should work fine if you have it all configured correctly.

SELECT *
FROM OPENDATASOURCE('SQLNCLI',
    'Data Source=ServerB;Integrated Security=SSPI;'
    ).MASTER.dbo.syscolumns

This will tell you your connection authentication type.

select auth_scheme from sys.dm_exec_connections where session_id=@@SPID

You want to get 'KERBEROS' here and not 'NTLM'.

It's a slippy slope, KERBEROS and Pass-through delegation, stick with it and you will eventually figure it out.

References Kerberos http://blogs.msdn.com/sql_protocols/archive/2005/10/12/479871.aspx

http://blogs.msdn.com/sql_protocols/archive/2006/12/02/understanding-kerberos-and-ntlm-authentication-in-sql-server-connections.aspx

http://blogs.iis.net/brian-murphy-booth/archive/2007/03/09/the-biggest-mistake-serviceprincipalname-s.aspx

Other manifestations of the problem http://www.sqlservercentral.com/Forums/Topic460425-359-1.aspx

http://msdn2.microsoft.com/en-us/library/aa905162(sql.80).aspx

http://msdn2.microsoft.com/en-us/library/ms189580.aspx

I hope this all helps.