The concept of a service was first introduced in Oracle8i as a means for the listener to perform connection load balancing between nodes and instances of a cluster. However, the concept,definition, and mplementation of services have been dramatically expanded. Services are a feature for workload management that organize the universe of work execution within the database to make that work more manageable, measurable, tunable, and recoverable. A service is a grouping of related tasks within the database with common functionality, quality expectations, and priority relative to other services. The notion of service provides a single-system image for managing competing applications running within a single instance and across multiple instances and databases.

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Using standard interfaces, such as DBCA, Enterprise Manager, and SRVCTL, services can be configured, administered, enabled, disabled, and measured as a single entity.Services provide vailability. Following outages, a service is recovered fast and automatically at surviving instances.

Services provide a new dimension to performance tuning. With services, workloads are visible and measurable. Tuning by “service and SQL” replaces tuning by “session and SQL” in the majority of systems where sessions are anonymous and shared.

Services are dynamic: The number of instances a service runs on can be augmented when load increases, and reduced when load declines. This dynamic resource allocation enables a costeffective solution for meeting demands as they occur.