SESSIONS

SESSIONS specifies the maximum number of sessions that can be created in the system. 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.

Oracle uses the default value of this parameter as its minimum. Values between 1 and the default do not trigger errors, but Oracle ignores them and uses the default instead.

The default values of the ENQUEUE_RESOURCES and TRANSACTIONS parameters are derived from SESSIONS. Therefore, if you increase the value of SESSIONS, you should consider whether to adjust the values of ENQUEUE_RESOURCES and TRANSACTIONS as well. (Note that ENQUEUE_RESOURCES is obsolete as of Oracle Database 10g release 2 (10.2).)

In a shared server environment, the value of PROCESSES can be quite small. Therefore, Oracle recommends that you adjust the value of SESSIONS to approximately 1.1 * total number of connections.