Wednesday, October 22, 2008

TNS-12516, ORA-12516,ORA-12519, TNS-12519 , ORA-12520

TNS-12516 TNS:listener could not find instance with matching protocol stack
ORA-12516, TNS:listener could not find available handler with matching protocol stack
TNS-12519 TNS: no appropriate service handler found

ORA-12519 TNS: no appropriate service handler found
ORA-12520 TNS:listener could not find available handler for requested type of server

If you see any of these errors you must increase the processes parameter.

Explanation

PMON is responsible for updating the listener with information about a particular instance such as load and dispatcher information. Maximum load for dedicated connections is determined by the PROCESSES parameter. The frequency at which PMON provides SERVICE_UPDATE is maximum at 10 minutes.

Since SERVICE_UPDATE 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.

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:

TNS-12516 TNS:listener could not find instance with matching protocol stack
TNS-12519 TNS:no appropriate service handler found

Additionally, an ORA-12520 error may appear in the listener log.

The output of the LSNRCTL services command will likely show that the service handler is "blocked".

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