How many sessions are allowed on the Oracle database?
The theoretical real number of maximum sessions depends on the horsepower of your server.
You determine the runtime maximum number of sessions with the SESSIONS parameter, which derives the PROCESSES parameter.
SQL> show parameter sessions
To see the existing maximum number of sessions, try this query:
select current_utilization, limit_value from gv$resource_limit where resource_name='sessions';
Try this to show info about both:
select resource_name, current_utilization, max_utilization, limit_value
from v$resource_limit
where resource_name in ('sessions', 'processes');