ORA-00030
Tried to kill a session, but it failed with ORA-00030.
SQL> ALTER SYSTEM KILL SESSION '1821, 8545, @2';
ALTER SYSTEM KILL SESSION '1821, 8545, @2'
*
ERROR at line 1:
ORA-00030: User session ID does not exist.
ORA-00030 means that the session information you provided in ALTER SYSTEM KILL SESSION statement is not found in V$SESSION of the instance. Sometimes, you might specify a wrong INST_ID.
Solutions
Most likely, the session has logged out itself or been killed before you issued ALTER SYSTEM KILL SESSION statement. Therefore, there's no such session ID (SID). So you don't have to take care of it anymore.
Chances are, the session runs in another instance. Therefore, we kill the session by specifying another INST_ID.
SQL> ALTER SYSTEM KILL SESSION '1821, 8545, @1';
System altered.
The case shows that providing a correct instance ID also matters for killing a session efficiently in a RAC database. In fact, there're various ways to kill or disconnect sessions for you to consider.