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Oracle ODBC error message: Unable to connect (ORA-12516)

Component

Oracle ODBC Driver

Version

21.12.0

Created on

Last modified on

No Workflow Applied

Review status

No Workflow Applied

KB article number

490341071

Summary

If you are using an Oracle database, establish an Oracle ODBC connection. After a database update or a database migration, an error with the following message may occur when testing the Oracle ODBC connection:

 Unable to connect

In addition, the following error code is displayed: "ORA-12516: TNS: Listener could not find an available handler with matching protocol stack."

The ORA error indicates that the specified maximum number of processes or session restrictions has been reached. In this case, a server cannot establish a connection to the database because the service handlers of the TNS listener are "blocked".

Important requirements

  • You have expert knowledge of Oracle and are an Oracle database administrator.

  • If your Oracle database is managed by an external service provider, please get in touch with the relevant contact person. If necessary, your edoc contact can also support you for a fee.

Solution

You must adapt your Oracle database so that more simultaneous requests are possible. In this way, you ensure that no service handlers of the TNS listener are blocked.