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Grid Clusters

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%.

When the IT technologists began examining grid computing, many mistakenly viewed the clusters as the grid environments. Adding to this confusion, vendors such as Sun Microsystems began calling their cluster offerings Grid Clusters. However, the clusters have different architecture, objective and purpose. Next, the true nature of the clustering technology will be examined.

What Is Cluster?

According to Greg Pfister, the guru of clustering,

?A cluster is a type of parallel system that consists of interconnected whole computers and is used as a single, unified computing resource?.

The whole computer is a normal combination of parts that comprise a stand-alone, usable computer. The components include one or more processors (including SMP and NUMA), memory, and I/O facilities. The whole computer is also referred to as a Node.

Thus, the cluster is a configuration of a group of independent servers, so that they appear on a network as a single machine. This group can be managed as a single system, shares a common namespace, and is designed specifically to tolerate component failures and to support the addition or subtraction of components in a way that is transparent to users. Figure 2.5 represents a 3-Node Cluster hosting a parallel database with three database instances residing on three hosts and providing jointly the database service.

Figure 2.5: A typical Cluster with 3-Nodes supporting Database Service

Why Clusters?

Symmetric multiprocessors (SMP) and non-uniform memory access (NUMA) systems have grown in size and power. It is very common to see SMP or NUMA systems equipped with 8 to 64 processors. They represent an alternative to cluster systems, but clusters have remained competitive and have made inroads into commercial application environments. There are obvious reasons for the survival of clusters: [Pfister]

* Performance - Throughput, response time, and turn around time is improved by using several machines at the same time. Clusters generate higher levels of performance.

* Availability - Clusters provide uninterrupted service by redistributing work, or through shifting the application services to surviving nodes by way of a failover process.

* Price/Performance - Clusters or other forms of computer aggregations are typically collections of machines that individually have very good performance for their price.

* Incremental Growth - It is easier to justify adding to a cluster than to buy a whole new computing facility.

* Scaling - Clusters have the ability to add capacity as needed.

* Manageability - Clusters have the ability to be managed as a single system.

Cluster Objectives

Traditionally, the term cluster was used to represent Server Clusters. Clustered systems are synonymous with a group of servers. The server, being the main layer or platform where the database or application service resides, is the most important component in providing availability and high performance.

Clusters, with multiple nodes, primarily aim at protecting server availability. Any failure in a server is transparent to end-users and is hidden by the failover of the application or database to a surviving node. End users or clients have access to the surviving node, thus allowing processing to continue. In another situation, a group of nodes are joined together to provide database services, as in a parallel database. Failure of a single node does not interrupt access to the database since the secondary nodes are still active in providing database access.

Thus, the cluster technology focuses on providing an alternative to a failed server. However, we have to realize that there are many other layers or components, each of which is significant in maintaining overall availability of the database or application service. Although the server (node) is a very crucial component and plays the key role in running the database or application, there are other components, such as the disk storage units and networking equipment for which alternatives or backups need to be provided to meet the failure conditions. The traditional concept of clustering revolves around server clustering only.

With this in mind, administrators and managers should provide adequate redundancy for other components in order to have an effective high availability environment.


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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