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Other titles in the Expert's Voice in Oracle series:
Cost-Based Oracle Fundamentalsby Jonathan Lewis
Synopses & Reviews
Every SQL query that is submitted to the Oracle database is analyzed by a SQL query optimizer called the Cost Based Optimizer (CBO). The CBO uses information about the structure, quantity, and nature of the data to work out the most efficient way to find your result. To be more precise, it tries to find the query execution plan that has the lowest execution cost.
As such, the CBO is one of the most important components of the Oracle database, knowledge and understanding of which are vital to the overall performance of the database and your Oracle applications. There are thousands of people whose job is to make Oracle databases run faster and yet, to many of them, the CBO is still the ultimate black box. The SQL queries go in, but if the execution times are "too slow" they have no real idea how to logically and effectively trace and fix the cause of the problem. This means that they can waste a lot of time of time (and money) on trial-and-error methods for getting SQL statements to perform efficiently.
One of the major difficulties, up till now, is that they there has been no single source of information explaining how Oracle's cost-based optimizer is supposed to work. In Cost Based Oracle, Jonathan Lewis completely demystifies the CBO, providing a lucid, thorough, and structured description of how the optimizer works, how it does its arithmetic, and the things you can do to make it behave.
In this book, volume 1 in a series of three, Jonathan covers the fundamentals: the things that everyone who uses the Oracle database needs to know about the CBO. It sheds light on the decisions the CBO makes when parsing a SQL statement and choosing an access plan. It demonstrates how the CBO calculates the cost of a plan and the rules and factors that go into these calculations. It reveals the basic assumptions the optimizer makes about the SQL and the data, explains why things go wrong and how you can fix them when those assumptions are incomplete, inaccurate, or simply false. He also includes a fabulous Upgrade Headaches section that is essential reading for anyone who has ever has, or ever will, upgrade between Oracle versions. Volumes 2 and 3 will track changes to the CBO in subsequent Oracle 10g releases, and will cover the more advanced and complex features of optimization.
Jonathan Lewis is one of the most highly respected Oracle consultants in the international community and in this book he shows you how to understand and use the CBO effectively, so that your SQL queries run as efficiently as possible and, ultimately, your applications fulfill their performance potential.
Book News Annotation:
Lewis, director of the UK Oracle User Group, describes the cost-based optimizer and other commonly used parts of the Oracle database model. An understanding of the model will allow readers to fix entire problem areas, not just single SQL statements, by adjusting the model or creating more truthful statistics. Focus is on selectivity and cardinality, access paths, and join order.
Annotation ©2006 Book News, Inc., Portland, OR (booknews.com)
Book News Annotation:
Lewis, director of the UK Oracle User Group, describes the cost-based optimizer and other commonly used parts of the Oracle database model. An understanding of the model will allow readers to fix entire problem areas, not just single SQL statements, by adjusting the model or creating more truthful statistics. Focus is on selectivity and cardinality, access paths, and join order. Annotation Â©2006 Book News, Inc., Portland, OR (booknews.com)
The question, Why isn?t Oracle using my index? must be one of the most popular (or perhaps unpopular) questions ever asked on the Oracle help forums. You?ve picked exactly the right columns, you?ve got them in the ideal order, you?ve computed statistics, you?ve checked for null columns?and the optimizer flatly refuses to use your index unless you hint it. What could possibly be going wrong?
If you?ve suffered the frustration of watching the optimizer do something completely bizarre when the best execution plan is totally obvious, or spent hours or days trying to make the optimizer do what you want it to do, then this is the book you need. You?ll come to know how the optimizer thinks, understand why it makes mistakes, and recognize the data patterns that make it go awry. With this information at your fingertips, you will save an enormous amount of time on designing and trouble-shooting your SQL.
The cost-based optimizer is simply a piece of code that contains a model of how Oracle databases work. By applying this model to the statistics about your data, the optimizer tries to efficiently convert your query into an executable plan. Unfortunately, the model can't be perfect, your statistics can't be perfect, and the resulting execution plan may be far from perfect.
In Cost-Based Oracle Fundamentals, the first book in a series of three, Jonathan Lewis? one of the foremost authorities in this field?describes the most commonly used parts of the model, what the optimizer does with your statistics, and why things go wrong. With this information, you?ll be in a position to fix entire problem areas, not just single SQL statements, by adjusting the model or creating more truthful statistics.
Table of Contents
What Do You Mean By Cost?- Tablescans.- Single-Table Selectivity.- Simple B-Tree Access.- The Clustering Factor.- Selectivity Issues.- Histograms.- Bitmap Indexes.- Query Transformation.- Join Cardinality.- Nested Loop Joins.- Hash Joins.- Sorting and Merge Joins.- The 10053 Trace.- Upgrade Headaches.- Optimizer-Related Parameters.
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