What is an Oracle Service
Oracle services were a feature introduced in Oracle 10g. Their function is to simplify workload management by allowing you to group applications that share traits such as thresholds, priorities and attributes.
The Oracle database is presented as a service and so you always have at least one service running. It is good practice to create at least one more service for application workloads and not to use the default Oracle service as it cannot by changed and will always allow connections.
One instance of a RAC database can support multiplke services and one service can spoan multiple instances. One service can support many applications, one or even a subset of one appliation.
You can create a service to accommodate batch users and another to deal with online users. Alternatively, you could assign a service to handle a particular application, application type or parts of an application etc.
It is recommended that you use a service to connect applications to the database and you do this by specifying the service name in the application’s connection string.
The resource manager is tightly integrated with services and you can control how and when services can run in an instance with it. It also allows scheduler jobs to tun as a service which allows you greater flexibility about how and when they run.