Example 8: Enlarging the User-Mode Stack Trace Database

The following GFlags command increases the maximum size of the user-mode stack trace database for myapp.exe, a fictitious program, from 8 MB to 24 MB.

The command uses the /i parameter to specify the image file. It uses the /tracedb parameter to set the maximum stack trace database size and the value 24 to indicate the size in megabytes. The command uses decimal units. (Hexadecimal units are not valid.)

gflags /i MyApp.exe /tracedb 24

As the following error message indicates, this command fails because the Create user mode stack trace database (+ust) flag is not set for the MyApp image file. You cannot set the size of a trace database until you create one.

Failed to set the trace database size for `MyApp.exe'

The following commands fix the error. The first command creates a trace database for myapp.exe and the second command sets the maximum size of the trace database to 24 MB. These commands cannot be combined into a single command. The following display shows the commands and the success message from GFlags.

gflags /i MyApp.exe +ust

Current Registry Settings for MyApp.exe executable are: 00001000
    ust - Create user mode stack trace database

gflags /i MyApp.exe /tracedb 24

Trace database size for `MyApp.exe' set to 24 Mb.

GFlags can change the size of the user-mode stack trace database, but it does not display it. To display the trace database size, use registry APIs, Regedit, or Reg (reg.exe), a tool included in Windows XP and Windows Server 2003, to check the value of the StackTraceDatabaseSizeInMB registry entry (HKLM\Software\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\ImageFileName\StackTraceDatabaseSizeInMB).

(A version of Reg is included in Windows XP, but that version does not permit the /v and /s switches in the same command.)

The following command uses Reg to query the value of StackTraceDatabaseSizeInMB:

reg query "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\MyApp.exe" /v StackTraceDatabaseSizeInMB 

In response, Reg displays the value of StackTraceDatabaseSizeInMB, which confirms that the new value, 24 (0x18), was set. This value becomes effective when you restart myapp.exe.


HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\MyApp.exe
    StackTraceDatabaseSizeInMB  REG_DWORD       0x18

Tip   Type the reg query command into Notepad, then save the file as tracedb.bat. Thereafter, to display the value of StackTraceDatabaseSizeInMB, just type TraceDb.