(1) ORA-12203 "TNS: unable to connect to destination"
- Potential cause is that the destination is not listening
- It may also be due to network problems
- You can issue a "lsnrctl status" at the host to see if the listener is running
- This may be related to the entry in the tnsname.ora file
(2) ORA-12535 "TNS: operation timed out"
- You should try tnsping first to start the diagnosis
- Look at the listener log on the host for more clues
- Check the sqlnet log files on the client side
- Run a statspack report, and check Top 5 timed events
Luckily the problem did not last long in production. The trouble ticket itself got closed out. But our DBA Team has an action item to determine why the problem happened, and prevent this from happening in the future.