Your database is open and the LISTENER listener is running. The new DBA of the system stops the listener by using the command: LSNRCTL> STOP What happens to the sessions that are presently connected…

There is no mechanism by which stopping the listener restricts active sessions to read-only operations - the listener is completely uninvolved in session activity after connection handoff.

The Oracle listener is solely responsible for brokering new incoming connection requests to the database. Once a client session is established and handed off to a dedicated server process or dispatcher, the listener plays no further role in that session's communication, so stopping the listener has no effect on currently connected sessions.

Sessions are not terminated and transactions are not rolled back; stopping the listener only closes the port for new connection requests and does not send any signal to existing server processes.

Existing sessions communicate directly with their server processes independent of the listener, so they are never blocked from performing operations when the listener is down.