Data services enable applications to become highly available and scalable services help prevent significant application interruption after any single failure within the cluster.
When you configure a data service, you must configure the data service as one of the following data service types:
Failover data service
Scalable data service
Parallel data service
Failover is the process by which the cluster automatically relocates an application from a failed primary node to a designated redundant secondary node. Failover applications have the following characteristics:
Capable of running on only one node of the cluster
Dependent on the cluster framework for high availability
If the fault monitor detects an error, it either attempts to restart the instance on the same node, or to start the instance on another node (failover), depending on how the data service has been configured. Failover services use a failover resource group, which is a container for application instance resources and network resources (logical hostnames). Logical hostnames are IP addresses that can be configured up on one node, and later, automatically configured down on the original node and configured up on another node.
Clients might have a brief interruption in service and might need to reconnect after the failover has finished. However, clients are not aware of the change in the physical server that is providing the service.
The scalable data service enables application instances to run on multiple nodes simultaneously. Scalable services use two resource groups. The scalable resource group contains the application resources and the failover resource group contains the network resources (shared addresses) on which the scalable service depends. The scalable resource group can be online on multiple nodes, so multiple instances of the service can be running simultaneously. The failover resource group that hosts the shared address is online on only one node at a time. All nodes that host a scalable service use the same shared address to host the service.
The cluster receives service requests through a single network interface (the global interface). These requests are distributed to the nodes, based on one of several predefined algorithms that are set by the load-balancing policy. The cluster can use the load-balancing policy to balance the service load between several nodes.
Sun Cluster systems provide an environment that shares parallel execution of applications across all the nodes of the cluster by using parallel databases. Sun Cluster Support for Oracle Real Application Clusters is a set of packages that, when installed, enables Oracle Real Application Clusters to run on Sun Cluster nodes. This data service also enables Sun Cluster Support for Oracle Real Application Clusters to be managed by using Sun Cluster commands.
A parallel application has been instrumented to run in a cluster environment so that the application can be mastered by two or more nodes simultaneously. In an Oracle Real Application Clusters environment, multiple Oracle instances cooperate to provide access to the same shared database. The Oracle clients can use any of the instances to access the database. Thus, if one or more instances have failed, clients can connect to a surviving instance and continue to access the database.