To check the status of a trace flag in SQL Server, you primarily use the DBCC TRACESTATUS command. This command allows you to see which trace flags are currently enabled, either globally or for the current connection.
Understanding SQL Server Trace Flags
Trace flags are used to temporarily set specific server characteristics or to switch off a particular behavior. They are often used to diagnose performance issues or debug stored procedures. Different trace flags affect the server in various ways, influencing query optimization, logging behavior, and other internal processes.
Using the DBCC TRACESTATUS Command
The most common and direct way to check the status of one or more trace flags is by using the DBCC TRACESTATUS command.
Syntax
The basic syntax for DBCC TRACESTATUS is:
DBCC TRACESTATUS ( [ [ trace# [ ,...n ] ] [ , -1 ] ] );trace#: The number of the trace flag whose status you want to check. You can specify multiple trace flags, separated by commas.-1: An optional parameter that checks the status of trace flags that are enabled globally. If-1is not specified,DBCC TRACESTATUSreturns the status of trace flags enabled for the current connection.- If no parameters are provided (
DBCC TRACESTATUS();), it returns the status of trace flags enabled for the current connection only.
Checking a Specific Trace Flag
As shown in the reference, to check the status of a specific trace flag, you provide its number:
dbcc tracestatus (4199);This command checks if trace flag 4199 is enabled for the current connection.
To check if trace flag 4199 is enabled globally:
dbcc tracestatus (4199, -1);Checking All Trace Flags
To check the status of all trace flags currently enabled for the current connection, run:
DBCC TRACESTATUS();To check the status of all trace flags currently enabled globally, run:
DBCC TRACESTATUS(-1);Interpreting the Output
The output of DBCC TRACESTATUS is a result set with three columns:
| Column Name | Description |
|---|---|
| TraceFlag | The number of the trace flag. |
| Status | Indicates if the trace flag is ON (1) or OFF (0). |
| Global | Indicates if the trace flag is enabled globally (1) or for the session (0). |
| Session | The session ID (SPID) for which the trace flag is enabled. |
Example Output (for dbcc tracestatus (4199) if the flag is on for the current session):
| TraceFlag | Status | Global | Session |
|---|---|---|---|
| 4199 | 1 | 0 | 55 |
This output indicates that trace flag 4199 is currently ON (Status = 1) for session ID 55 (Session = 55) and is not enabled globally (Global = 0).
Example Output (for dbcc tracestatus (4199, -1) if the flag is on globally):
| TraceFlag | Status | Global | Session |
|---|---|---|---|
| 4199 | 1 | 1 | -1 |
This output indicates that trace flag 4199 is currently ON (Status = 1) and is enabled Globally (Global = 1). The Session ID -1 indicates it's global.
Related Commands
While checking trace flags, you might also need to turn them on or off.
- Turn a trace flag ON: Use
DBCC TRACEON (trace#, [-1]). For example,DBCC TRACEON (4199, -1)turns trace flag 4199 on globally. - Turn a trace flag OFF: Use
DBCC TRACEOFF (trace#, [-1]). As shown in the reference,dbcc traceoff (4199, -1);turns trace flag 4199 off globally.
After turning a flag on or off, you can re-run DBCC TRACESTATUS to verify the change, as demonstrated in the reference: dbcc tracestatus (4199);.
Using DBCC TRACESTATUS is a quick and effective way to monitor which trace flags are active on your SQL Server instance or for your specific connection.
