ORA-12154 ALWAYS only occurs on SQL Client & no SQL*Net packets ever leave client system
involves the listener, the database itself or anything on the DB Server.
ORA-12154 occurs when client requests a connection to some DB server system using some connection string.
The lookup operation fails because the name provided can NOT
be resolved to any remote DB.
The analogous operation would be when you wanted to call somebody, but could not find their name in any phonebook.
The most frequent cause for the ORA-12154 error is when the connection alias can not be found in tnsnames.ora.
The lookup operation of the alias can be impacted by the contents of the sqlnet.ora file; specifically DOMAIN entry.
TROUBLESHOOTING GUIDE: ORA-12154 & TNS-12154 TNS:could not resolve service name [ID 114085.1]