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Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

Clustering Software

Clustering software is usually equipped with the functionality of monitoring, detection of failures, and managing the cluster components, which include the servers and server connections. Cluster software specializes in failure detection by use of software probes, fault isolation, and fault containment wherever applicable.

Cluster software is usually referred to as Cluster Manager or Operating system dependent layer (OSD) as in the case of Oracle Real Application clusters. Cluster Software is generally provided by the Cluster hardware manufacturer. However, in the case of OSD layer for Oracle RAC system for Windows 2000 cluster and Linux, Oracle provides the cluster software. For building the 10g RAC database system, Oracle provides an integrated and portable ClusterWare called Cluster Ready Services (CRS).

The failure detection process involves the determination of a fault condition and the application of a proper response. A failure could result in a switch-over to a secondary component or may result in the total shutdown of the failing component, in which case some kind of reconfiguration takes place. As an example, if two interconnects are configured, fault or loss of one would not cripple the cluster but merely result in shutting it off. Whereas when one of the nodes hangs, cluster manager evicts the failed node and informs other members so that the application (database instance) can take necessary reconfiguration action.

The Cluster Manager is also responsible for node monitoring, which includes the polling of status of various resources like inter-connect hardware/software, shared disks, Oracle instances and public networks. In Oracle RAC, Cluster Manager interacts with the Global Cache Service of RAC to reconfigure the failed instance resources. The Cluster manager interacts with RAC modules and helps to reconfigure the system resources as required.

Cluster software protects against the conditions of Split-Brain and Amnesia. The Split-Brain Condition occurs when all communication between nodes is lost and the cluster becomes partitioned into sub-clusters, each believing that it is the only partition. Amnesia occurs when the cluster restarts after a shutdown with cluster configuration data older than at the time of the shutdown. Changes in cluster membership drive the cluster reconfiguration sequence that may, in turn, result in services being migrated from failed or faulty nodes to healthy ones. More details about the Split-Brain condition are covered in later sections.

In Failover Clusters, along with cluster software, cluster vendors usually supply agents or bundled scripts to control and manage the failover process. Agents are available for most of the widely used databases such as Oracle, Sybase and DB2. Agents follow preconfigured and deterministic tested procedure to initiate resources and start the database on the surviving node.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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