While developing software odd things happen sometimes like your server loosing the database connection without reason. Either there is no connection or the database is at its limits. To check the quantity of open connections on an Oracle database, we can run the following script.
select * from v$resource_limit where limit_value not like '%UNLIMITED%' and rtrim(ltrim(limit_value)) not like '0' order by limit_value;
The result will look something like this: