初始化参数
SERVICE_NAMES
列出实例所属的服务。在启动时，每个实例及其属于相同服务的其他实例，被注册到所有监听器。在数据库操作期间，每个服务的实例将 CPU
使用和当前的连接计数等有关信息， 传递给监听相同服务的所有监听器。这种通信实现了动态负载平衡和连接的故障转移
Service Registration：
Service registration is a feature by which the PMON process dynamically registers instance information with a listener, which enables the listener to forward client connection requests to the appropriate service handler. PMON provides the listener with information about thefollowing:
1.Names of the database services provided by the database 2.Name of the database instance associated with the services and its current and maximum load 3.Service handlers (dispatchers and dedicated servers) available for the instance, including their type, protocol addresses, and current and maximum load
Service registration is dynamic and does not require configuration in the listener.ora file. Dynamic registration reduces administrative overhead for multiple databases or instances.
The initialization parameter SERVICE_NAMES lists the services an instance belongs to. On startup, each instance registers with the listeners of other instances belonging to the same services. During database operations, the instances of each service pass information about CPU use and current connection counts to all listeners in the same services. This communication enables dynamic load balancing and connection failover.