The insights that Jonathan provides into the workings of the cost-based optimizer will make a DBA a better designer, and a Developer a better SQL coder. Both groups will become better troubleshooters.- Thomas Kyte, VP (Public Sector), Oracle Corporation
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?nd 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?l come to know how the optimizer ?hinks,·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?ne of the foremost authorities in this field?escribes the most commonly used parts of the model, what the optimizer does with your statistics, and why things go wrong. With this information, you?l be in a position to fix entire problem areas, not just single SQL statements, by adjusting the model or creating more truthful statistics.
Author Information
Jonathan Lewis
Jonathan Lewis has been involved in database work for more than 19 years, specializing in Oracle for the last 16 years and working as a consultant for the last 12 years. Jonathan is currently a director of the UK Oracle User Group (UKOUG) and is well known for his many presentations at the UKOUG conferences and SIGs. He is also renowned for his tutorials and seminars about the Oracle database engine, which he has held in various countries around the world.
Jonathan authored the acclaimed book Practical Oracle 8i (Addison-Wesley, 2001), and he writes regularly for the UKOUG magazine and occasionally for other publications, including OTN and DBAZine. He also finds time occasionally to publish Oracle-related material on his website, JL Computer Consultancy.
