Oracle Internals: An Introduction

Chapter 1. Introduction

Why are people so intensely interested in Oracle internals? Partly because internals information can be useful for tuning and troubleshooting. But also because Oracle Corporation has kept most of the internals secret, while revealing just enough to tantalize.

In fact, Oracle internals information is needed only for advanced performance tuning. It’s true that basic application tuning is the kind of tuning that’s most often needed, and the kind that has the biggest impact. Nevertheless, there are times when advanced performance tuning is necessary, and that is when you need a deep understanding of how Oracle works. This book provides some of the foundations for that understanding.

To appreciate the contribution that this book makes, and to put it in context, you need to have a basic understanding of the layers of the Oracle kernel.

The Oracle Kernel Layers

The Oracle kernel is comprised of layers; the main layers are shown in Figure 1.1. Each layer depends upon the services of the layers below it, and may call any of them directly, in any order. However, control is never passed up the stack, except when returning from a call.

The one apparent exception to this rule is that the data layer and the transaction layer sometimes need to perform recursive transactions for tasks such as index block splits or extent space management, and recursive calls are needed for tasks such as trigger execution or SQL statement execution from within stored program units. However, ...