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Chapter 3: Oracle Database Concepts

3.1 Introduction

In the previous chapter various hardware architectures, such as SMP, MPP, NUMA, etc., were discussed at length. Also explored was the usage of clustered SMP architecture as a prudent solution for businesses with data processing needs. This architecture allows businesses to provide data storage and retrieval to users and to support increased growth of users through linear scalability. When many systems are joined together to work as a cohesive unit, they support not only the scalability factor but also the availability factor. This is on the assumption that an appropriate clustered operating system is used. When one system or node in the cluster fails, the users have other nodes that could be used to route their request to get to the required information. Consequently, clustering provides linear scalability, which means more nodes or systems could be added into the mix without much difficulty. More availability is provided due to the fact that when one node in the cluster fails, the failure of one node in the cluster does not down the system, as the other nodes are available to process the required information.

These functionalities, or features, provided by the clustered SMP architecture make it a suitable solution for Oracle RAC. In the clustered architecture, the operating system helps provide sharing of resources (e.g., the disk subsystem) between all the participating nodes in the cluster. With RAC, Oracle, which sits on top of the clustered operating system, provides a shared database among two or more Oracle instances, and users access the database via these instances. Such a configuration provides a clustered database solution.

In this chapter, the concepts of a single instance configuration of Oracle, new features in Oracle 9i compared against similar features in Oracle 8i, and the basic implementation of RAC as an extension to the single, or stand-alone, configuration of Oracle will be discussed. Background processes used in a RAC implementation and their basic functionality along with the changes from the previous versions of RAC will be covered. Additionally, some of the basic extensions in Oracle that would change when implemented with the RAC feature, such as free lists, free list groups, etc., will be highlighted.

The primary focus of this chapter, and future chapters, will be with respect to RAC; however, where it becomes important, the old feature will be discussed from a comparison perspective. The occasional highlights comparing RAC with OPS will provide help to the database administrator migrating from OPS to RAC.