SQL Server Error Collection

error # 22:26 2014-7-30 Reset the number of connections
The maximum number of concurrent connections, such as connections to an instance, is not particularly understandable, yesterday afternoon, a whim, the number of connections to 1, constantly open a new query window, and did not follow the expected error (did not restart the database service). Open the computer this morning, open Object Explorer, connect to the server times wrong.

viewing errorlog, the error message is obvious, exceeding the maximum number of concurrent connections.

 the- -- -  the: *:37.12Login Error:17809Severity: -State:3.  the- -- -  the: *:37.12Login Could notConnect because the maximum Number  of '1' UserConnections has already been reached. The system administrator can Usesp_configure toIncrease the maximum value. The connection has been closed.[Client: 127.0.0.1]

The first reaction, using a DAC connection, changes the user connections to a larger point. Start the database in single-user mode before referencing the default instance, but it starts with an error.
It is generally known that a named instance causes single-user-mode startup to fail, but does not know how to modify the code. Find the information on the web, and then view the database instance corresponding to the service's properties, in the general options, the path to the executable file: "D:\SQL2012\MSSQL11." Sql12\mssql\binn\sqlservr.exe "-ssql12
-S is followed by the instance name, so refer to this line of code to modify the single user mode start cmd command to:

- -sSQL12

Of course, you can also add-m directly to the startup parameters of the service properties
Find the corresponding private port from the log information, DAC connection, view current maximum concurrency, indeed 1, reset max concurrency via user connections
Question 1, the log information does not say to the DAC connection to set up, just said system administrator can operate, but in the case of 1, it is obviously not possible to operate through the GUI, but should be able to directly through SQLCMD or new query modified.
The maximum number of concurrent numbers set under the problem 2,gui is actually reflected in the sysconfigures.config=103 corresponding value, which requires restarting the database service to take effect, which limits the maximum number of records sysprocesses.spid>50