PHYSICAL DATABASE DESIGN - Fundamentals of Database Management Systems - page 199

CHAPTER 8

PHYSICAL DATABASE

DESIGN

I f computers ran at infinitely fast speeds and data stored on disks could be found
and brought into primary memory for processing literally instantly, then logical
database design would be the only kind of database design to talk about. Well structured,
redundancy-free third normal form tables are the ideal relational database structures and,
in a world of infinite speeds, would be practical, too. But, as fast as computers have
become, their speeds are certainly not infinite and the time necessary to find data stored
on disks and bring it into primary memory for processing are crucial issues in whether
an application runs as fast as it must. For example, if you telephone your insurance
company to ask about a claim you filed and the customer service agent takes two minutes
to find the relevant records in the company's information system, you might well become
frustrated with the company and question its ability to handle your business competently.
Data storage, retrieval, and processing speeds do matter. Regardless of how elegant
an application and its database structures are, if the application runs so slowly that it
is unacceptable in the business environment, it will be a failure. This chapter addresses
how to take a well structured relational database design and modify it for improved
performance.

OBJECTIVES

Describe the principles of file organizations and access methods. ■

Describe how disk storage devices work.

■

Describe the concept of physical database design.

■

List and describe the inputs to the physical database design process. ■

Describe a variety of physical database design techniques ranging from adding
indexes to denormalization.

■

CHAPTER OUTLINE
Introduction
Disk Storage
The Need for Disk Storage
How Disk Storage Works

File Organizations and Access Methods
The Goal: Locating a Record
The Index
Hashed Files