When connecting to an Oracle database, typically your database server will have tnsnames.ora, which is a configuration file that informs the server about NET_SERVICE_NAMES which are valid database connections. When a request is received, the listener processes and forwards that request onto the appropriate Oracle database server using a service handler, which just acts as the connection between the listener and the database server. This broker application is known as the listener and it performs the task of listening for incoming client requests. When a client is attempting to connect to an Oracle database, rather than connecting to the database directly, there is a broker service that intervenes and handles the connection request for the client. A SERVICE_NAME will typically follow the format of the SID followed by the database domain, like so: DB_UNIQUE_NAME.DB_DOMAIN The TNS Listener SERVICE_NAMES, on the other hand, represent the names by which database instances can be connected to. For example, the SID of our bookstore database, as seen in in the full global database name of. Often the SID is the prefix word or DB_UNIQUE_NAME that precedes the DB_DOMAIN. In Oracle, the system identifier (or SID) is a local identifier of up to eight characters in length that is used to identify a particular database and differentiate it from other databases on the system. It is important to understand the (slight) difference between what Oracle defines as a SID compared to a SERVICE_NAME, as we’ll use this information to create a proper connection string later on. To properly resolve this error and connect to the appropriate Oracle database, we’ll need to expound a bit on how Oracle behaves and, therefore, what is causing this issue in the first place.
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