A poorly performing database application not only costs users time, but has an impact on other applications running on the same computer or the same network. SQL Tuning provides the essential next step for SQL developers and database administrators who want to extend their SQL tuning expertise and get the most out of their database applications. Content includes how to understand and control SQL execution plans, and how to diagram SQL queries to deduce the best execution plan for the query. Each chapter includes exercises to reinforce concepts, and SQL Tuning concludes by addressing special cases and "outside the box solutions to unsolvable problems."

Dan Tow is an independent consultant, operating under the banner SingingSQL (www.singingsql.com). His experience solving Oracle-related performance problems goes all the way back to his 1989 hire by Oracle Corporation. During most of his tenure at Oracle, Dan focused on the performance of Oracle Applications, managing the performance group for that division. In this role, he found a fertile testing ground for his SQL tuning method applied to the huge set of complex SQL included in those applications, including both online SQL and diverse batch processes. In 1998, Dan left Oracle to lead performance for TenFold Corporation, where he applied the same methods to tuning questions on DB2, and SQL Server, and Sybase, as well as on Oracle. In 2002, Dan started his own business, SingingSQL, through which he offers diverse database-related tuning services, including SQL tuning and systematically analyzing load to learn which SQL should be tuned. He has introduced his SQL tuning method to over 1,000 people in short lectures, and now offers in-depth courses in the material, using this book as textbook. Dan has a Ph.D. in chemical engineering from the University of Wisconsin at Madison. He lives in Palo Alto, California, and can be reached at dantow@singingsql.com.

Foreword

xi

Preface

xiii

1. Introduction

1

(7)

Why Tune SQL?

1

(2)

Who Should Tune SQL?

3

(1)

How This Book Can Help

4

(2)

A Bonus

6

(1)

Outside-the-Box Solutions

7

(1)

2. Data-Access Basics

8

(35)

Caching in the Database

9

(3)

Tables

12

(3)

Indexes

15

(3)

Uncommon Database Objects

18

(4)

Single-Table Access Paths

22

(5)

Calculating Selectivity

27

(9)

Joins

36

(7)

3. Viewing and Interpreting Execution Plans

43

(30)

Reading Oracle Execution Plans

44

(10)

Reading DB2 Execution Plans

54

(11)

Reading SQL Server Execution Plans

65

(8)

4. Controlling Execution Plans

73

(35)

Universal Techniques for Controlling Plans

73

(11)

Controlling Plans on Oracle

84

(14)

Controlling Plans on DB2

98

(4)

Controlling Plans on SQL Server

102

(6)

5. Diagramming Simple SQL Queries

108

(26)

Why a New Method?

108

(2)

Full Query Diagrams

110

(16)

Interpreting Query Diagrams

126

(2)

Simplified Query Diagrams

128

(2)

Exercises

130

(4)

6. Deducing the Best Execution Plan

134

(42)

Robust Execution Plans

134

(2)

Standard Heuristic Join Order

136

(1)

Simple Examples

137

(8)

A Special Case

145

(2)

A Complex Example

147

(4)

Special Rules for Special Cases

151

(23)

Exercise

174

(2)

7. Diagramming and Tuning Complex SQL Queries

176

(52)

Abnormal Join Diagrams

177

(26)

Queries with Subqueries

203

(13)

Queries with Views

216

(9)

Queries with Set Operations

225

(2)

Exercise

227

(1)

8. Why the Diagramming Method Works

228

(10)

The Case for Nested Loops

228

(2)

Choosing the Driving Table

230

(3)

Choosing the Next Table to Join

233

(3)

Summary

236

(2)

9. Special Cases

238

(12)

Outer Joins

238

(5)

Merged Join and Filter Indexes

243

(3)

Missing Indexes

246

(1)

Unfiltered Joins

247

(1)

Unsolvable Problems

248

(2)

10. Outside-the-Box Solutions to Seemingly Unsolvable Problems

250

(19)

When Very Fast Is Not Fast Enough

250

(4)

Queries that Return Data from Too Many Rows

254

(11)

Tuned Queries that Return Few Rows, Slowly

265

(4)

A. Exercise Solutions

269

(13)

B. The Full Process, End to End

282

(13)

Glossary

295

(8)

Index

303

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