Database Administrators Stack Exchange is a question and answer site for database professionals who wish to improve their database skills and learn from others in the community. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. If I understand correctly, it should be possible by using "admin:" prefix before the server name, but I receive the following message:. Dedicated administrator connections are not supported via SSMS as it establishes multiple connections by design. You cannot connect the object explorer with the DAC. The nature of object explorer is that it uses multiple connections, which is not allowed with the DAC.
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SQL Server provides a special diagnostic connection for administrators when standard connections to the server are not possible. This diagnostic connection allows an administrator to access SQL Server to execute diagnostic queries and troubleshoot problems even when SQL Server is not responding to standard connection requests. The DAC only allows changing the user context to another admin user.
The dedicated admin connection DAC can help you out of a sticky situation. This was built to help you connect to SQL Server and run basic queries in cases with critical performance problems. This works by telling SQL Server to reserve a thread specifically for processing your queries in an emergency. While it does reserve a connection for you, it is only one thread, there is no parallelism happening here, in fact, you will receive an error. Typically, what ends up happening and where it can help is when your SQL Server is screaming for resources, but there are none are available. In my experience, this has been related to long-running queries that are not optimized for data the end user wants to return or your SQL Server not allowing new connections. With the DAC you are now able to find the long-running query and kill that session or troubleshoot the issue. When first learning about DAC, you will quickly see that it is enabled by default, however, it is only for connections that are originating from the local system. Technically speaking this is because out of the box it is only listening to the local loopback IP
The Dedicated Administrator Connection DAC is a handy tool for a variety of tasks, ranging from snooping around in the definition of system objects, all the way to recovering an unresponsive SQL Server. There are a number of reasons why the connection may fail, and this tip walks through the problems and helps you get it working again. Microsoft has a good troubleshooting starting point here and I have listed many of the causes for errors here. Right-click the instance, select Properties, and move to the Startup Parameters tab. There you want to add -T, click Apply, and then restart the service. Ashish Kumar Mehta talked about this in a previous tip. Note that DAC is disabled by default in Express since the connection pre-allocates resources, and Express Edition is already artificially resource constrained. Note that a service restart will be required:. Next, you can check if the remote admin connections instance-level configuration setting is enabled:.