session:
Because every login requires a session, this parameter effectively determines the maximum number of concurrent users in the system. You should always set this parameter explicitly to a value equivalent to your estimate of the maximum number of concurrent users, plus the number of background processes, plus approximately 10% for recursive sessions.
12c (1.5 * PROCESSES) + 22
ALTER SYSTEM can be used in a PDB only to change the value of the SESSIONS parameter for that PDB. (仅限在PDB中修改)
For a CDB, the root container's SESSIONS parameter specifies the total number of sessions for the database.
the SESSIONS parameter does not count recursive sessions and hence does not require the 10% adjustment.
process --- For the operating system process (not detailed here, exclusive and shared mode), and session is the db layer, the two concepts are different.
The attempts involved here are: (the concept can be viewed in the official file)
gv$session
gv$process
v$resource_limit
v$license