ORA-12500: TNS:listener failed to start a dedicated server process
ORA-12500: TNS:LISTENER FAILED TO START A DEDICATED SERVER PROCESS
The most common cause of a ORA-12500 is a busy system whereby PGA RAM is exhausted.
The solutions are:
- Reduce sort_area_size (pga_aggregate_target) and hash_area_size to make each default PGA size smaller.
- Add additional server RAM
- As a last resort, deploy shared servers (the Multithreaded Server (MTS).
Common syntax issues in the listener.ora file can cause numerous listener connection problems, most notably the “ORA-12500: TNS: listener failed to start a dedicated server process” error.
Sometimes this ORA-12500 is because of a PGA RAM shortage on the target database, based on the settings for pga_aggregate_target, sort_area_size and hash_area_size.
You can have a single listener, pointing to multiple Oracle instances, each on a different version.