Disconnect session Vs kill -9

Question

Hello
Is there any difference between "alter system disconnect session" and kill -9.
As far as I know, both kill the dedicated server process.

Answer 1

oradba wrote:
For 'alter system disconnect session' refer to the documentation for your unknown database versionIn documentation we can find this
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_2013.htm#BABEBJFA
"The IMMEDIATE setting disconnects the session and recovers the entire session state immediately, without waiting for ongoing transactions to complete."
I've tried to reproduce this
session 1
SQL> create table t_big as select lpad('*',4000,'*') id from dual connect by level <= 100000;
Table created.
Elapsed: 00:00:24.52
SQL> update t_big set id = lpad('+',4000,'+');
100000 rows updated.
Elapsed: 00:12:58.66
SQL> select sid, serial# from v$session where sid = userenv('sid');
       SID    SERIAL#
       147       3489
Elapsed: 00:00:00.12
SQL> rollback;
session 2
SQL> select t.USED_UBLK, z.SID, z.SERIAL#, z.status, p.SPID
  2    from v$transaction t, v$session z, v$process p
  3   where t.ADDR = z.tADDR(+)
  4     and z.pADDR = p.addr(+);
USED_UBLK        SID    SERIAL# STATUS   SPID
     55431        147       3489 ACTIVE   3024
Elapsed: 00:00:00.01
SQL>
SQL> alter system disconnect session '147,3489' immediate;
alter system disconnect session '147,3489' immediate
ERROR at line 1:
ORA-00031: session marked for kill
Elapsed: 00:00:00.02
SQL>
SQL> begin dbms_lock.sleep(5); end;
  2  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.03
SQL>
SQL> select t.USED_UBLK, z.SID, z.SERIAL#, z.status, p.SPID
  2    from v$transaction t, v$session z, v$process p
  3   where t.ADDR = z.tADDR(+)
  4     and z.pADDR = p.addr(+);
USED_UBLK        SID    SERIAL# STATUS   SPID
     52754        147       3489 KILLED   3024
Elapsed: 00:00:00.02
SQL>As you can see, "alter system disconnect session ... immediate" have the same effect as "alter system kill session ... immediate".
But
C:\Windows\system32>orakill ora10db 3024
Kill of thread id 3024 in instance ora10db successfully signalled.disconnects session immediately.
Can anyone explain what is the difference between "alter system disconnect session ... immediate" and "alter system kill session ... immediate"?
p.s. oracle 10.2.0.4, 11.2.0.1; oracle dedicated server mode; windows;