Chapter 6: Parallel Processing

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6.1 Introduction

In the previous chapter transaction management principles of a single stand alone Oracle configuration were examined. Subsequently, additional steps of a transaction in an RAC environment were also discussed. During these discussions, we examined the normal day-to-day operations, such as when users query the database and when users perform a DML operation.

Almost everyone will have experienced a major traffic jam while driving in one of the major cities on a superhighway. What if these superhighways only had one lane (other lanes are closed due to construc tion) with every commuter lined up behind another? Clearing traffic jams could potentially take hours. Consequently, superhighways consist of several lanes so that traffic can be distributed over them all. Creating more and more lanes provides for more opportunity for simultaneous or parallel movement of vehicles, thus resulting in a quicker commute time.

The same theory could be applied to the information technology arena. If there were a large number of users making requests to the database simultaneously (or one user making a large request to retrieve a complex set of data) and there was only one CPU to process the request(s), the user(s) would have to wait several hours, or possibly days, for the results. (The length of the wait would be based on the complexity of the query, underlying database design, processing power of the computer, the volume of data being retrieved, etc.). If there were an opportunity for the user(s) to make distributed calls (multiple processors) to the database, the request would complete much more quickly and efficiently. Multiple CPUs on the computer system allow for distribution of requests among the available processors.

The six lanes of traffic movement and processing of data across multiple processors are possible because of the division of work amongst the available resources. This division of work into multiple, or asynchronous processing of a request is called a parallel activity or parallel processing.

In this chapter the concept of parallel processing will be discussed. The advantages and disadvantages of parallel processing, the architecture, implementation and functionality of parallel processing using various options of Oracle will be covered.

Information regarding the basic rules of implementing a parallel processing environment under RAC, how it is configured, what the performance benefits are, and tuning issues around it will also be included.

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