How to solve repetitive ORA-2391 error in DBeaver 4.3.3.1
I found the solution thanks to Balazs. There are a couple of options in the Preferences window that could generate multiple sessions.


The first one is at Preferences > General > Editors > SQL Editor, Connections group and "Open separate connection for each editor" option.
The other one is at Preferences > Database > Metadata, Metadata group and "Open separate connection for metadata read" option.


Both options must be unchecked in order to avoid creation of multiple sessions for same connection, therefore to avoid ORA-02391 error.