16.3.10 ORA-12516

Indicates that the listener is unable to find an available handler with the matching protocol stack.

Message

ORA-12516: Cannot connect to database.
Listener at string does not have a protocol handler 
  for string ready or registered for service string.
(CONNECTION_ID=string)

For example:

ORA-12516: Cannot connect to database. 
Listener at host 10.9.7.5 port 1522 does not have protocol handler
  for tcp ready or registered for service sales_service.example.com. 
(CONNECTION_ID=1ABcDEabCd1aB+AbCdE1aB==)

Cause

The connection is refused by the Oracle Database listener process. None of the known and available service handlers for the specified service name support the client's requested protocol stack.

Action

1. Check for mistakes in the specified connection string.

2. If you are using a cloud service, then review the connection string shown in the cloud service console.

3. Wait a moment, and then try to connect again. The service handler may be in a blocked state and not accepting new connections.

4. Use the CONNECTION_ID value to track this connection attempt in trace files for further diagnosis.

5. Check which handlers are currently known by the listener and are accepting connections by performing one of these tasks:

   • Ask your database administrator.

   • Review the connection string in the cloud service console.

   • If you have access to the machine where the listener is running, then run one of the following:

     • lsnrctl services

     • If a listener is named in the listener.ora file, then run:

       lsnrctl services listener_name

     • If an Oracle Connection Manager (Oracle CMAN) proxy listener is named in the cman.ora file, then run:

       cmctl show services -c cman_name

     • If an Oracle Global Service Manager (Oracle GSM) listener is named in the gsm.ora file, then run:

       gdsctl services -raw -gsm gsm_name

   • Ensure that the registered handlers are configured to support the required protocol stack. For example, to match the protocol, session, and presentation used in the connection string.