ORA-00018 maximum number of sessions exceeded
Cause: All session state objects are in use.
Action: Increase the value of the SESSIONS initialization parameter.
ORA-00018 comes under "Oracle Database Server Messages". These messages are generated by the Oracle database server when running any Oracle program.
How to increase SESSION initialization parameter:
1. Login as sysdba
sqlplus / as sysdba
2. Check Current Setting of Parameters
3. If you are planning to increase "sessions" parameter you should also plan to increase "processes and "transactions" parameters.
A basic formula for determining these parameter values is as follows:
4. These paramters can't be modified in memory. You have to modify the spfile only (scope=spfile) and bounce the instance.