How Serviceguard Works with Oracle Real Application Clusters

Serviceguard provides the cluster framework for Oracle, a relational database product in which multiple database instances run on different cluster nodes. A central component of Real Application Clusters is the distributed lock manager (DLM), which provides parallel cache management for database instances. Each node in a RAC cluster starts an instance of the DLM process when the node joins the cluster, and the instances then communicate with each other over the network.

The Distributed Lock Manager is an internal component of the Real Application Clusters software. The group membership service (GMS) is the means by which Oracle instances communicate with the ServiceGuard cluster software. GMS runs as a separate daemon process that communicates with the cluster manager. This daemon is an HP component known as cmgmsd.

The cluster manager starts up, monitors, and shuts down the GMS daemon. When an Oracle instance starts, the instance registers itself with GMS; thereafter, if an Oracle instance fails, GMS notifies other cluster nodes to perform recovery. If GMS dies unexpectedly, ServiceGuard will fail the node with a TOC (Transfer of Control).