ORA-02391:exceeded simultaneous SESSIONS_PER_USER limit

ORA-02391 is user session error. It means you need to kill some user session if its not required or you need to increase sessions per use limit. Killing sessions can be very destructive if you kill the wrong session so be careful when killing session. for that first we need to identify that sessions for that query is given below. . SQL>SELECT s.inst_id, s.sid,s.serial#,p.spid,s.username,s.program FROM   gv$session s JOIN gv$process p ON p.addr = s.paddr AND p.inst_id = s.inst_id WHERE  s.type != 'BACKGROUND'; The basic syntax for killing sessions is given below. SQL>ALTER SYSTEM KILL SESSION 'sid,serial#,@inst_id' immediate; if you want to increase user session process are given below: 1) SELECT name, value FROM gv$parameter WHERE name = 'resource_limit'; 2) ALTER SYSTEM SET resource_limit=TRUE SCOPE=BOTH; 3) SELECT name, value FROM gv$parameter WHERE name = 'resource_limit'; 4) ALTER PROFILE <profile name>  LIMIT sessions_per_user 80;