A colleague of mine discovered that many of our linked-server SQL queries were running very slowly on SQL Servers running Windows Server 2008 and Windows Server 2008 R2. Since the linked-server SQL queries ran perfectly on Windows Server 2003 servers, the issue had to be Windows Server 2008+ specific. The culprit ended up being the Windows Scaling Heuristics and TCP Auto-Tuning that are enabled by default on Windows Vista, Windows 7, Windows Server 2008, and Windows Server 2008 R2.

To remedy the situation, Windows Scaling Heuristics and TCP Auto-Tuning simply need to be disabled.

  1. On the SQL server open an elevated Command Prompt window (run Command Prompt as Administrator)

  2. To disable Windows Scaling Heuristics, run the following command:

  3. To disable TCP Auto-Tuning, run the following command:

  4. Restart the SQL Server server (a reboot is not necessary, just restart the SQL service)

After disabling Windows Scaling Heuristics and TCP Auto-Tuning you should see a noticable increase in performance on your linked-server SQL queries.


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