A colleague was deleting million plus rows from a table , when others tried connecting to the Oracle database their sessions seemed to hang. Just trying to find a cause for this as I believe this shouldn't have happened. The deletion didnt use the nolog option and the archived redo logs were full , but go no errors in the alert file. The Undo tablespace reached its maximum and was unable to grow any further. Would any of these stop people connecting ? The cpu utilisation on the server was very low. The solution ended up killing oracle and restarting the server, but just trying to find a root cause. in the Listener.log, everything looked normal and was still accepting connections,and another user was doing a full table scan select on the table that was having rows deleted. But still no reason for users not being able to connect, even as sysdba locally