SERVICE_NAMES specifies one or more names by which clients can connect to the instance. The instance registers its service names with the listener. When a client requests a service, the listener determines which instances offer the requested service and routes the client to the appropriate instance.
What is the reason for I modify the parameter service_names like this
Service_names = 'service_one','service_two'
Service_names = 'service_one'
Because in the same database you have multiple applications, multiple workloads,... and services help to: - identify sessions when troubleshooting performance issue - manage resources for those with higher or lower priority - balance between several nodes - offload some read-only workloads to a standby database ...