Dedicated Administrator Connection It is rare, but SQL Server can stop responding to normal queries and appear to be frozen. How could this happen? Consider that when you bought the system that houses SQL Server, you likely planned for future growth and usage. No matter how much time and effort you put into this plan, though, some companies just outgrow their servers too quickly, and the servers can’t handle the workload. In a scenario like this, it is possible that SQL Server might stop responding to normal queries. To troubleshoot this issue, or any kind of problem where SQL Server just isn’t responding to normal calls, you need the Dedicated Administrator Connection (DAC). The DAC is a special diagnostics connection that is always available for connection, even under normal operating circumstances. As the name implies, only administrators (members of the sysadmin server role) can connect to the DAC to run diagnostic queries and trou...
~ a resource for the Microsoft SQL Server.