Using Serviceguard Extension for RAC, 4th Edition, February 2007

Introduction to Serviceguard Extension for RAC
Overview of SGeRAC and Oracle 9i RAC
Chapter 124
Overview of SGeRAC and Oracle 9i RAC
This section describes some of the central components for SGeRAC and
Oracle 9i RAC.
How Serviceguard Works with Oracle 9i RAC
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 Oracle instance starts and the
instances then communicate with each other over the network.
Group Membership
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 cmgmsd.
When an Oracle instance starts, the instance registers itself with
cmgmsd; thereafter, if an Oracle instance fails, cmgmsd notifies other
members of the same group to perform recovery. If cmgmsd dies
unexpectedly, Serviceguard will fail the node with a TOC (Transfer of
Control).