11.1 Introduction

In the previous chapter, we looked at the high-availability and scalability features of a clustered database solution such as RAC. RAC provides other normal features such as recoverability, manageability, and maintainability found in a stand-alone configuration of Oracle. However, availability and scalability are naturally derived from the architecture of the database configuration.

Hardware and operating system clustering provides failover opportu nities when a member in the cluster fails, thus providing continuous availability of the application to the users. Apart from the clustered failover options available at the operating system level, Oracle provides additional failover options through the TAF implementation. TAF pro vides transparent failover of the users' sessions from the failed instance to one of the other available instances. Much of the working of TAF, its configuration, implementation, and some performance aspects, was also discussed in the previous chapter.

With the introduction of Oracle 9 i and the enhancement to the clustered database solution from the earlier version of OPS, considerable improvements have been made regarding the cache fusion technology, allowing users to access data from any instance participating in the clustered configuration and Oracle to transfer the information across the cluster interconnect. This feature of cache fusion replaces the expensive pinging activity that occurred in the earlier versions of Oracle.

OPS implementations required that the applications were specifically designed to use the clustering technology. This is because when an instance requested records that were already being worked against on another specific instance, the blocks that contained...