You check for active trace flags by running the following query. They may be global or they may be session based.
Checking for active trace flags
DBCC TRACESTATUS
The output could be something like the following.
TraceFlag Status Global Session --------- ------ ------ ------- 4199 1 1 0 4616 1 1 0 (2 row(s) affected) DBCC execution completed. If DBCC printed error messages, contact your system administrator.
If there are no active trace flags you will only see
DBCC execution completed. If DBCC printed error messages, contact your system administrator.
Enable session based trace flags
To enable trace flags only in your session use the following two commands.
DBCC TRACEON (trace#) DBCC TRACEOFF (trace#)
trace#
Is the number of the trace flag to turn on.
Enable trace flags globally
DBCC TRACEON (trace#,-1) DBCC TRACEOFF (trace#,-1)
-1
Switches on the specified trace flags globally.
To enable a trace flag to persist through a restart. Alter the “Startup Parameters” in the Advanced tab for the SQL Server service in SQL Server Configuration Manager.
One example would be.
Before modification
-dC:Program FilesMicrosoft SQL ServerMSSQL10.MSSQLSERVERMSSQLDATAmaster.mdf;-eC:Program FilesMicrosoft SQL ServerMSSQL10.MSSQLSERVERMSSQLLogERRORLOG;-lC:Program FilesMicrosoft SQL ServerMSSQL10.MSSQLSERVERMSSQLDATAmastlog.ldf
After modification
-dC:Program FilesMicrosoft SQL ServerMSSQL10.MSSQLSERVERMSSQLDATAmaster.mdf;-eC:Program FilesMicrosoft SQL ServerMSSQL10.MSSQLSERVERMSSQLLogERRORLOG;-lC:Program FilesMicrosoft SQL ServerMSSQL10.MSSQLSERVERMSSQLDATAmastlog.ldf;-T4199
sqlservr [-sinstance_name] [-c] [-dmaster_path] [-f]
[-eerror_log_path] [-lmaster_log_path] [-m]
[-n] [-Ttrace#] [-v] [-x] [-gnumber] [-h]
References
DBCC TRACEON (Transact-SQL)
DBCC TRACEOFF (Transact-SQL)
DBCC TRACESTATUS (Transact-SQL)
Trace Flags (Transact-SQL)