Oracle Listener refused connection ORA-12519 troubleshooting
Oracle database 11gR2 (18.104.22.168.2)
New database connection attempts to Oracle database 11gR2 fail with following Oracle error:
Listener refused the connection with the following error: ORA-12519, TNS:no appropriate service handler found [SQLCode: 12519], [SQLState: 66000] None None
One of the most common reasons for the TNS-12516 and/or TNS-12519 Oracle error being reported on Oracle 11gR2 is the configured maximum number of PROCESSES and/or SESSIONS limitation being reached. When this occurs, the service handlers for the TNS Listener become “Blocked” and no new connections can be made. Once the TNS Listener receives an update from the PMON process associated with the database instance telling the TNS Listener the thresholds are below the configured limit, and the database is now accepting connections connectivity resumes.
There are different ways to check if a database instance reaches the maximum number of processes on Oracle 11gR2. One of the quickest SQL see below:
select * from v$resource_limit where resource_name = 'processes';
If this is the case, to fix this Oracle error, increase the PROCESSES parameter value to allow the Oracle database Listener to spawn more server process as required in your environment.
It might be further investigation required though.
Sometimes when listener throws a TNS error the number of actual processes can be below the limit. See below why this can happen.
When the listener believes the current number of connections has reached maximum load, it may set the state of the service handler for an instance to “blocked” and begin refusing incoming client connections with either of the following errors: ora-12519 or ora-12516. Once the TNS Listener receives an update from the PMON process associated with the Database instance telling the TNS Listener the thresholds are below the configured limit, and the database is then accepting connections connectivity resumes. The listener counts the number of connections it has established to the instance but does not immediately get information about connections that have terminated. Only when PMON updates the listener via SERVICE_UPDATE is the listener informed of current load. Since this can take as long as 10 minutes, there can be a difference between the current instance load according to the listener and the actual instance load.
If you really reached the processes limit and it stays this way for some time you will probably get the following error trying to connect:
ORA-00020: maximum number of processes (%s) exceeded
There are a couple of ‘workarounds’ for this issue … but no real solution at this time (even for Oracle 11.2) since you are not capable to connect to the DB even as SYSDBA:
- Use an existing connection with sufficient privileges (if one is logged on) to view V$SESSION / V$PROCESS and kill some sessions:
alter system kill session ‘SID, SERAL#’;
- Stop a less critical application, DB monitoring, etc.
- Kill one or more of the client connections on OS level:
* UNIX: kill -9
* WINDOWS: using ORAKILL …
If none above helps and the error occurs often, shut down Oracle, increase the PROCESSES parameter in the initialization parameter file, and restart Oracle.