How to use orakill.exe?
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SQL> select sid, spid as thread, osuser, s.program 
2 from sys.v_$process p, sys.v_$session s
3 where p.addr = s.paddr;

       SID THREAD       OSUSER                         PROGRAM
---------- ------------ ------------------------------ -------------------------------
         1 2084         SYSTEM                         ORACLE.EXE
         2 1992         SYSTEM                         ORACLE.EXE
         3 1812         SYSTEM                         ORACLE.EXE
         4 660          SYSTEM                         ORACLE.EXE
         5 1924         SYSTEM                         ORACLE.EXE
         6 2068         SYSTEM                         ORACLE.EXE
         7 428          SYSTEM                         ORACLE.EXE
         8 1880         SYSTEM                         ORACLE.EXE
         9 1884         sgenis-us\sgenis               sqlplusw.exe

9 rows selected.

Say the query from user scott is consuming lot resources and it can be killed by running orakill utility as follows.

C:\>orakill 9 1884