Overview of Oracle Global Data Services Configuration

Learn how Global Data Services manages global and local database services, centralizes service configuration, and coordinates service availability across Oracle databases to database clients.

A Global Data Services configuration consists of a set of global services for database clients. A global service is a database service managed and made available across multiple physical databases (which may be in different locations, data centers, or clusters) that are part of a GDS configuration. These global services enable users and applications to connect using a single logical service name. The GDS framework manages routing, load balancing, and failover across all databases that offer the global service. A global service manager serving a Global Data Services configuration is aware of all global services the configuration provides and acts as a mediator for database clients and databases in the configuration. A client program connects to a regional global service manager and requests a connection to a global service. The client does not need to specify a particular database or instance. The global service manager forwards the client's request to the optimal instance in the configuration that offers the global service. Ensure all your database clients that use the same global service share service-level requirements.

The functionality of local services, defined as traditional database services provided by a single database, does not change when you use global services. Oracle Database can provide local and global services simultaneously. A client application can also use both global and local services simultaneously.

The configuration and runtime status of global services are stored in the Global Data Services catalog. Each database offering global services also maintains information about those services in a local repository, such as a system dictionary or Oracle Cluster Registry, and data on local services. Global services stored in a local repository include a flag to distinguish them from traditional local services.

If you are locally connected to a particular database, you can query data on global services provided by that database. You can configure, modify, start, or stop a global service using the Global Data Services Control utility (GDSCTL) when you are connected to the Global Data Services catalog, so you can ensure centralized, coordinated management of global services. You cannot configure, modify, start, or stop a global service using the Server Control utility (SRVCTL) or the Oracle Clusterware Control utility (CRSCTL).

Note:

Under certain circumstances (such as patching a database or clusterware software), you can stop or start global services using SRVCTL with the -force option with the appropriate command. You must have the appropriate system privileges.

After you configure global services for a Global Data Services configuration, the global service manager manages global services on GDS configuration databases according to the properties you specify when you create the services.

When a database joins the configuration, or if a database restarts after a shutdown, the database registers with all global service managers in the configuration. After receiving the registration request, one of the global service managers queries the GDS catalog and checks whether all global services that the database is supposed to provide are created there and have the correct attributes. If a discrepancy exists between the information in the catalog and the database, then the global service manager may create, delete, or modify global services in the database or change their attributes to synchronize them with the catalog. The global service manager then determines which global services need to run on the database and starts them as needed.

The global service manager can start or stop a global service in a database. However, if the database is an Oracle RAC database, then the global service manager does not control which particular instances within the database offer the service. Service management is controlled by the clusterware and the administrator of the Oracle RAC database.

When a database instance in a Global Data Services configuration fails, all global service managers in the configuration are notified about the failure and stop forwarding requests to the instance. If the instance belongs to a noncluster database or is the last instance available in an Oracle RAC database, then, depending on the configuration, a global service manager can automatically start the service on another database in the Global Data Services pool where the service is enabled. If you decide to manually move a global service from one database to another using the appropriate GDSCTL command, then the global service manager stops and starts the service on the corresponding databases.

Parent topic: Oracle GDS Architecture and Concepts