Error: ORA-00020: maximum number of processes (string) exceeded
Cause: All process state objects are in use.
Action: Increase the value of the PROCESSES initialization parameter.
Solution: You have to increase processes parameter value.
ORA-00020 is caused by two things:
1- A lot of idle that is not working (zombie) connection. You can kill this connections from database. Maybe also you have to kill proceses at the operating system level witk kill -9 command.
2- Too few process parameter value. Oracle provides limit for the number of connected processes with the processes parameter. Also you may get the ORA-00020 error due to system resourse limit.
Calculating amount of sessions and transactions parameter values with below formula.
processes=x
sessions=x*1.1+5
transactions=sessions*1.1
You can show and increase processes parameter like below.
SQL> show parameter processes;
processes integer 150
SQL> alter system set processes=300 scope=spfile;
SQL> shutdown immediate;
SQL> startup;
You should set the processes parameter to a very high value because it consumers very little resources and you do not want your instance to “lock up” with the ORA-0018 error.
Also, you can look this topic: https://www.fatihacar.com/blog/ora-00018-maximum-number-of-sessions-exceeded/