Oracle SQL Internals Handbook. Donald K. Burleson Joe Celko Dave Ensor Jonathan Lewis Dave Moore Vadim Tropashko John Weeg

Transcription

1 Oracle SQL Internals Handbook Donald K. Burleson Joe Celko Dave Ensor Jonathan Lewis Dave Moore Vadim Tropashko John Weeg

2 Oracle SQL Internals Handbook By Donald K. Burleson, Joe Celko, Dave Ensor, Jonathan Lewis, Dave Moore, Vadim Tropashko, John Weeg Copyright 2003 by BMC Software and DBAzine. Used with permission. Printed in the United States of America. Series Editor: Donald K. Burleson Production Manager: John Lavender Production Editor: Teri Wade Cover Design: Bryan Hoff Printing History: August, 2003 for First Edition Oracle, Oracle7, Oracle8, Oracle8i and Oracle9i are trademarks of Oracle Corporation. Many of the designations used by computer vendors to distinguish their products are claimed as Trademarks. All names known to Rampant TechPress to be trademark names appear in this text as initial caps. The information provided by the authors of this work is believed to be accurate and reliable, but because of the possibility of human error by our authors and staff, BMC Software, DBAZine and Rampant TechPress cannot guarantee the accuracy or completeness of any information included in this work and is not responsible for any errors, omissions or inaccurate results obtained from the use of information or scripts in this work. Links to external sites are subject to change; dbazine.com, BMC Software and Rampant TechPress do not control or endorse the content of these external web sites, and are not responsible for their content. ISBN:

3 Table of Contents Conventions Used in this Book...ix About the Authors...xi Foreword...xiii Section One - SQL System Tuning Chapter 1 - Parsing in Oracle SQL... 1 Parsing in SQL by Vadim Tropashko...1 Chapter 2 - Are We Parsing Too Much? Are We Parsing Too Much? by John Weeg What is Identical? How Much CPU are We Spending Parsing? Library Cache Hits Shared Pool Free Space Cursors Code Do What You Can Chapter 3 - Oracle SQL Optimizer Plan Stability Plan Stability in Oracle 8i/9i by Jonathan Lewis The Back Door to the Black Box Background / Overview Preliminary Setup What Does the Application Want to Do? What Do You Want the Application to Do? From Development to Production Oracle 9 Enhancements Caveats Conclusion Chapter 4 - SQL Tuning Using dbms_stats Query Tuning Using DBMS_STATS by Dave Ensor Introduction Table of Contents iii

4 Test Environment Background Original Statement With Hash Join Hints Oracle's Cost-based Optimizer CPU Cost Key Statistics Other Factors Cursor Sharing Package DBMS_STATS Plan Stability Getting CBO to the Required Plan Localizing the Impact Ensuring Outline Use Postscript Conclusions Section Two - SQL Statement Tuning Chapter 5 - Trees in SQL Trees in SQL: Nested Sets and Materialized Path by Vadim Tropashko Adjacency List Materialized Path Nested Sets Nested Intervals Partial Order The Mapping Normalization Finding Parent Encoding and Sibling Number Calculating Materialized Path and Distance between nodes The Final Test Chapter 6 - SQL Tuning Improvements iv Oracle SQL Internals Handbook

5 SQL Tuning Improvements in Oracle 9.2 by Vadim Tropashko Access and Filter Predicates V$SQL_PLAN_STATISTICS Chapter 7 - Oracle SQL Tuning Tips SQL tuning by Don Burleson Chapter 8 - Altering SQL Stored Outlines Faking Stored Outlines in Oracle 9 by Jonathan Lewis Review The Changes New Features Old Methods (1) Old Methods (2) The Safe Bet Conclusion References Section Three - SQL Index Tuning Chapter 9 - Using Bitmap Indexes with Oracle Understanding Bitmap Indexes by Jonathan Lewis Everybody Knows What Is a Bitmap Index? Do Bitmaps Lock Tables? Consequences of Bitmap Locks Problems with Bitmaps Low Cardinality Columns Sizing Conclusion References Chapter 10 - SQL Star Transformations Bitmap Indexes 2: Star Transformations by Jonathan Lewis 105 The Bitmap Star Transformation Table of Contents v

6 Warnings Conclusion References Chapter 11 - Bitmap Join Indexes Bitmap Indexes 3 Bitmap Join Indexes by Jonathan Lewis It's fantastic - What's the Problem What Is a Bitmap Join Index? Issues Conclusion References Section Four - SQL Diagnostics Chapter 12 - Tracing SQL Execution Oracle_trace - the Best Built-in Diagnostic Tool? by Jonathan Lewis How Do I? What is oracle_trace Uses for oracle_trace Putting it All Together Some Results Now What? The Future Conclusion Caveat References Chapter 13 - Embedding SQL in Java & PL/SQL Java vs. PL/SQL: Where Do I Put the SQL? by Dave Moore The Power of a Package The Flexibility of Java Performance Benchmarks vi Oracle SQL Internals Handbook

7 Environment The Tests Java: PL/SQL: Multiple Statements Java: PL/SQL: Truncate Java: PL/SQL: Benchmark Results Single Statement Results Multiple Statements Results Truncate Results Remote Results Conclusion Chapter 14 - Matrix Transposition in Oracle SQL Matrix Transposition in SQL by Vadim Tropashko Nesting and Unnesting Integer Enumeration for Aggregate Dismembering User Defined Aggregate Functions Section Five - Advanced SQL Chapter 15 - SQL with Keyword Searches Keyword Searches by Joe Celko Chapter 16 - Using SQL with Web Databases Web Databases by Joe Celko Chapter 17 - SQL and Calculated Columns Calculated Columns by Joe Celko Introduction Triggers INSERT INTO Statement Table of Contents vii

8 UPDATE the Table Use a VIEW Index viii Oracle SQL Internals Handbook

9 Parsing in Oracle SQL CHAPTER 1 Parsing in SQL SQL is a high abstraction level language used exclusively as an interface to Relational Databases. Initially it lacked recursion, and, therefore, had a limited expression power, but eventually this construct has been added to the language. Here we'll explore how convenient SQL is for general-purpose programming. SQL programming is very unusual from procedural perspective: there is no explicit flow control, in general, and no loops, in particular, no variables either to apply operations to, or to store intermediate results into. SQL heavily leverages predicates instead. Our goal is writing a simple predicate expression parser in SQL. Given an expression like this, (((a=1 or b=1) and (y=3 or z=1)) and c=1 and x=5 or z=3 and y>7) the parser should output a tree like this OR AND AND OR a = 1 b = 1 OR y = 3 Parsing in SQL 1

10 c = 1 x = 5 AND z = 3 y > 7 z = 1 Recursive descent parser is the easy way to approach the task. Unfortunately, Oracle didn t implement recursion yet, and as I work for Oracle, it clearly is the database of my choice. In cases where a programmer can t use recursion, (s)he resorts to iteration. We approach the task by building the set of all subclauses, and then selecting only well formed expressions. It s clearly more work than in procedural programming, but that s typical SQL attitude: write a query first and let optimizer worry about efficiency. In order to generate all the subclauses we need a table of integers. Before Oracle 9i we had to take a real table, and add a pseudo column like this: select rownum from all_objects where all_objects is a big enough table. In Oracle 9i we use table function instead: 2 Oracle SQL Internals Handbook