0045-0048

Previous Table of Contents Next

Page 45

CHAPTER 4

Overview of the
Oracle Architecture

IN THIS CHAPTER

  • Computer Architecture Fundamentals 46
  • Global View of the Oracle Architecture 47
  • Oracle Files 51
  • System and User Processes 53
  • Oracle Memory 58
  • Storage 61
  • System Database Objects 64
  • Protecting Your Data 66
  • Backup and Recovery 72
  • Distributed Databases 77
  • National Language Support 77
  • Data Warehousing 78
  • Following a SQL Statement Through the Architecture 79

Page 46

This chapter describes the components of the Oracle database software that are present (in one form or another) on all machines on which the Oracle database can run. We describe the various components (including memory, process, hardware, and network components ) and discuss the interaction between them. In addition, we discuss some of the internal objects (such as rollback segments) so that you can have a greater understanding of the inner functioning and setup of the database.

Computer Architecture Fundamentals

This section gives a very brief overview of the architecture present in all computers; keep in mind, however, that a standalone machine might not have any network connections.

Memory

Memory is a storage device in a computer chip into which instructions and data are entered and retrieved when needed for processing. It is thousands, if not hundreds of thousands, times faster to read information from memory rather than directly from disk; however, there must be an initial load of information into memory from disk. The larger the memory available for a machine, the quicker it will run.

As far as Oracle is concerned , the instructions are the Oracle programs, and the data is the data read from the Oracle database files.

Processes/Programs

A process or program is a set of instructions to a computer that are run on the machine's processor. These instructions, or programs, are stored on the file system of the machine. Before you can run a program, the instructions for it are read into the machine's memory from the file system.

For Oracle, the processes are the Oracle system (background) processes that look after the database or the user processes that perform work for the user accessing the database.

File Systems

Data and programs for the computer are stored on the machine's file system, which typically consists of one or more hard disks. Programs and data, when required, are loaded from the hard disk into the machine's memory before the program or data is used.

Oracle uses the file system for the sets of the files that make up the database and the software programs that enable you to access the database.

Network

A network is a system of connections between machines that enable one machine to communicate with another and share resources. As well as the physical wires and components, you need to establish a set of rules for communication; this is known as a protocol.

Page 47

Oracle can support many different types of networks and protocols. If you require communication between machines running Oracle software, you must install the Oracle SQL*Net software on all machines requiring network access.

Global View of the Oracle Architecture

The Oracle architecture described in this section is the generic architecture that applies to all platforms on which Oracle runs. There might be differences in the architecture between different platforms, but the fundamentals are the same.

What Is a Database?

A database is a collection of related data that is used and retrieved together for one or more application systems. The physical location and implementation of the database is transparent to the application programsand in fact, you could move and restructure the physical database without affecting the programs.

Figure 4.1 illustrates the concept of a database holding data for many different (possibly unrelated) applications.

Figure 4.1.
Database with data for
many applications.

Physically, in its simplest form, an Oracle database is nothing more than a set of files somewhere on disk. The physical location of these files is irrelevant to the function (although important for the performance) of the database. The files are binary files that you can only access using the Oracle kernel software. Querying data in the database files is typically done with one of the Oracle tools (such as SQL*Plus) using the Structured Query Language (SQL).

Logically, the database is divided into a set of Oracle user accounts (schemas), each of which is identified by a username and password unique to that database. Tables and other objects are owned by one of these Oracle users, and access to the data is only available by logging in to the database using an Oracle username and password. Without a valid username and password for the database, you are denied access to anything on the database. The Oracle username and

Page 48

password is different from the operating system username and password. For example, a database residing on a UNIX machine requires that I log in to the UNIX machine using my UNIX operating system username and password and then log in again to Oracle before I can use the database objects. (The UNIX login would not be required for a client/server setup.) This process of logging in, or connecting to, the database is required whether you're using an Oracle or non-Oracle tool.

The same table name can coexist in two separate Oracle user accounts; although the tables might have the same name, they are different tables. Sometimes, the same database (same set of physical database files) is used for holding different versions of tables (in separate Oracle accounts) for the developers, system testing, or user testing, or the same table name is used in different application systems.

Often, people refer to an Oracle user account as a database, but this is not strictly correct. You could use two Oracle user accounts to hold data for two entirely different application systems; you would have two logical databases implemented in the same physical database using two Oracle user accounts.

In addition to physical files, Oracle processes and memory structures must also be present before you can use the database.

Figure 4.2 shows the basic Oracle architecture that I discuss throughout this chapter.

Figure 4.2.
The basic Oracle
architecture.

Previous Table of Contents Next


Oracle Unleashed
Oracle Development Unleashed (3rd Edition)
ISBN: 0672315750
EAN: 2147483647
Year: 1997
Pages: 391

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net