Checking the maximum number of simultaneous connections is possible in the dictionary:
SELECT NAME, VALUE FROM V $ PARAMETER WHERE NAME = ‘sessions’;
Checking how many connections are currently connected is possible in this way:
SELECT COUNT (*) FROM V $ SESSION;
Obviously, both things are checked at the system level.
Of course, you can change the maximum number of connections:
ALTER SYSTEM SET SESSIONS = 400 SCOPE = SPFILE;
Configuration changes will take effect after the reboot.