About _disable_txn_alert undocumented parameter - at least as for Oracle 11g win32.
This parameter is connected with ktsmgd_ global variable.
This variable is actually bitmap. Default value is 0. Bits which are checked within Oracle 11g processes: 1, 2, 4, 8, 0x10, 0x20, 0x40, 0x80, 0x100, 0x200.
Thus, turn on trace flags will be: 0x4 + 0x8 + 0x20 + 0x40 = 0x6C or 108 decimal. Or turn on all flags: 0x1 + 0x2 + 0x4 + 0x8 + 0x10 + 0x20 + 0x40 + 0x80 + 0x100 + 0x200 = 0x3FF or 1023 decimal.
Note: ksdwrf() function write trace information to files usually named <SID>_<process_name>_<thread_id>.trc, at the folder which is usually defined by background_dump_dest parameter.
Update: this command is also can be used for viewing state of ktsmgd_ variable: oradebug dumpvar SGA ktsmgd_
Update: Article where Yong Huang make use of this parameter.
→ [list of blog posts]