16.3.11 ORA-12520

Indicates that the listener cannot find an available handler for the requested server type.

Message

ORA-12520: Cannot connect to database.
Listener at string does not have handler 
  for string server type
  ready or registered for service string.
(CONNECTION_ID=string)

For example:

ORA-12520: Cannot connect to database. 
Listener at host 10.9.7.5 port 1522 does not have handler
  for pooled server type 
  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 handlers for the requested server type (dedicated, shared, or pooled) is appropriate for the client connection.

Action

1. Check for mistakes in the specified connection string.

2. Ensure that the SERVER parameter in the connection string or that the tnsnames.ora file connect descriptor specifies a server type (dedicated, shared, or pooled) that is supported by handlers known by the listener.

3. If using an Easy Connect connection string, then check that the specified server type is supported by handlers known by the listener.

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

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

6. 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 shown 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