Oracle ora-12519:tns:no appropriate service handler found resolution __oracle

Sometimes you have to go to the database and sometimes you can't even.

It is possible that the current number of connections on the database has exceeded the maximum value that it can handle.

Select COUNT (*) from v$process--current number of connections

select value from v$parameter where name = ' processes '--maximum number of connections allowed by database

modification Max Number of calls:

alter system set processes = Scope = SPFile;


Restart database:
shutdown immediate;
startup;

--See which users are currently using

the data SELECT osuser, a.username,cpu_time/executions/1000000| | ' S ', sql_fulltext,machine from 

v$session A, V$sqlarea b

where a.sql_address =b.address order by cpu_time/ executions desc;

View the number of current sessions

  Select COUNT (*) from v$session;

To view the maximum number of processes in a database

Show parameter processes

To view the maximum number of sessions in a database

Show parameter Sessions

modifying processes and Sessions values

Alter system set PROCESSES=300 Scope=spfile;
Alter system set SESSIONS=300 Scope=spfile;

Reference
Reference