Oracle Net Services software provides the ability to define all the components of a distributed network, including all
- database servers,
- listeners, and
- database links.
This global definition is called a topology.
To support the topology, Oracle Net Services enables Oracle databases to connect to each other in a seamless fashion. Connectivity is first established in Oracle by defining service names
in a special file. In Oracle Net Services, a service name is a name that is used to uniquely identify each Oracle database.
Usually a service name is the same as the database name (ORACLE_SID), but it can be different. The service name is translated by Oracle to obtain all the information it needs to connect to the remote database.
Connect identifiers are stored in a directory server for all clients to access. Depending on the number of clients, there can be a significant load on a directory server. During a connect identifier lookup, a name is searched under a specific Oracle Context. Users expect relatively quick performance so the database connect time is not affected. Because of the scope of the lookup, users may begin to notice slow connect times if lookups takes more than one second. You can resolve performance problems by changing the network topology or implementing replication.
In the next lesson, we will continue our examination of Oracle's topology solution with a look at the role of database links in establishing database connectivity.