Oracle Clusterware Diagnosis - Expert Oracle RAC Performance Diagnostics and Tuning - page 534

Chapter 16
Oracle Clusterware Diagnosis
Webster's Dictionary 's definition for a cluster is “a number of similar things that occur together.” A clustered system
occurs when things of the same sort are organized together or growing together to form or represent a group of their
respective kind. For example, a number of people, flowers, or things grouped together forms a cluster. Similarly,
a group of independent hardware systems or nodes that is interconnected to provide a single computer source is
referred to as a hardware cluster. Unlike with flowers and other objects, if one node in a cluster fails, its workload is
automatically distributed among the surviving nodes. This process of automatically distributing the workload to other
available nodes reduces the downtime of the entire system. Clustering is an architecture that keeps systems running
in the event of a single-system failure. Clustering provides maximum scalability by grouping separate servers into a
single computing facility. Clusters have the potential to provide excellent price and performance advantages over
traditional mainframe systems in many areas, such as availability, scalability, manageability, and recoverability.
Clustering has proven to be a successful architecture of choice for providing high availability (HA) and scalability
in business-critical computing applications. Clients interact with a cluster as though it were a single entity or a
single high-performance, highly reliable server. If a cluster fails, its workload is automatically distributed among the
surviving nodes.
Oracle Clusterware
Oracle Clusterware is an application stack that resides on top of the basic operating system (O/S). Apart from
the primary function of managing the nodes participating in the cluster, Oracle's clusterware offers additional
services that provide a more comprehensive solution compared to third-party cluster managers. It's the clusterware
component that's responsible for restarting RAC instances and listeners upon process failures and relocating the VIPs
upon node failure. Oracle provides various utilities and commands to manage the various tiers of the clusterware.
Figure 16-1 illustrates the Oracle Grid Infrastructure (GI) stack in Oracle Clusterware 11g Release 2. There are
several high availability daemons introduced in this release.