73 of 73 people found the following review helpful:
5.0 out of 5 stars
Quick solutions for difficult optimization problems, January 24, 2004
This review is from: SQL Tuning (Paperback)
"Tell me something I don't already know", that's what crosses my mind every time I pick up a new performance, tuning book. If you're like me, 90% of the content in any DBA book in the store is 'old hat'.
This book is refreshing. It doesn't waste time going over all of the stuff you learned years ago.
Knowing how to read an execution plan or when to pick a hash join over a nested loop join is not what this book is about. There are plenty of books on the market that cover basic, vendor specific, query tuning. I personally have about 20 of these books on my bookshelf here at home. (Over the years I've worked on Sybase, SQL Server, Informix XPS, & Oracle.)
Here's the deal...
Anyone who has worked with really big systems will eventually run into an optimization problem that seems to be unsolvable. You can try histograms, compressed key indexes, partitioning, pre-joined indexes, and materialized views, but you still can't get the performance that's being requested. For a DBA, it can be a very frustrating dilemma. This is especially true when you know from the data volume that you should be able to get there.
The truth is, optimizers can't always get the right solution, even with correct statistics. There are some good technical reasons why this is true, but that's out of scope for my review. In any case, that's where this book comes to the rescue. I feel that it gives you some insight into the optimization problem and tells you how to correct the problems that your optimizer can't figure out.
This book is NOT for use on 95% of your queries. Most optimizers will pick the correct access plan if the DBA does his/her job correctly and collects the appropriate statistics.
In my experience, I get two types of problems that I have trouble getting the optimizer to solve:
#1. Joining together a large number (8-14) of tables. At least 1 or 2 of the tables have over 30G of real data. By `real data', I mean that 30G of data is actually populated.
#2. Making high transaction queries read the fewest amount of buffers in order to get rid of latching problems.
After I read the first few diagramming chapters of this book, I thought I'd give it a try on a problem that was recently solved at work. I was surprised. It worked, and even with my clumsiness with the method, it only took me about 2 hours to get a solution. It took us about 3 days at work. Our trial and error solution was slightly better, than what I came up with using the author's method. However, it was so close that had I used his method, I most certainly would have gone on to another problem. (The author's solution was strange because I would never have solved the join order the way that he did. His solution actually had me pick the largest table, out of 10, to drive the query. I thought this was odd because my test query had some very good filters on smaller tables.)
These were the results per execution:
Optimizer - 100K buffers.
Trial & Error - 1700 buffers.
Book method (basic graphing) - 2000 buffers.
If I had known about this book, I could have solved this problem in a few hours. Instead it took several DBA's, a few day's time to come up with a solution that was only marginally better.
Since this method appeared to work so well for OLTP, I went back and looked at a very large OLAP query that I had worked on last year. I and several developers had spent days trying to get it to run faster. Even with the author's method, I still couldn't make it better, but I was happy to see that the join order picked by the optimizer was almost identical to what I had calculated using the book.
I plan on studying this guide over and over until I've memorized this method. I don't think it will solve every problem, but I think it gives you an edge over using experience alone.
Before you purchase this book...
Keep in mind, that SQL tuning is fundamentally *not a simple problem*, so readers should not buy the book expecting an easy list of simple tips and tricks. (If the problem was easy, the optimizer likely would have got it right in the first place, and you wouldn't be tuning!) The correct solution to the problem is fairly complex, as complex as it *needs* to be.
Also, it's not noted anywhere, but I gathered that the author assumes that the reader will have basic high school Algebra skills, and will have taken a basic statistics course in order to fully understand the reasoning behind the explanations. Although, Algebra and statistical knowledge are probably not necessary to learn the tuning method presented. I state this because I told a good friend about this book, and his first question was, "Does it have a lot of math to go through?" So, if statistics is not your thing, don't worry. The author only presents enough information to give you a level of comfort that his method is based on mathematics. He doesn't require that you know "graph theory" or anything like that.
By the way, our change from 100K buffers per transaction to 1700 buffers, dropped the CPU utilization for the website that was running the OLTP query by about 70%. That was on a 16 CPU, Sun/Solaris box. So proper SQL tuning can save you a lot of $$$.
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14 of 14 people found the following review helpful:
5.0 out of 5 stars
A Work of Genius, July 21, 2006
This review is from: SQL Tuning (Paperback)
I have withdrawn my earlier review because I did not properly understand the importance of this book until the second reading. That is a difficult admission to make since my business is database performance tuning.
This book is about tuning SQL queries in a systematic and scientific manner. It is above all about determining the optimum order in which the query engine should access the tables involved. My quibble was that join order is only a part of the whole tuning problem and most of the time the query optimizer got it right anyway. While this is true, I see now that it misses the point.
The fact that the optimizer gets it right so often allows us to take join order for granted. But how do we know the optimizer got it right unless we know what the optimum join order is? That is what this book teaches, a methodology and an elegant system of notation that allows us to determine the optimum join order of the most complex query. As the author points out, the number of possible join orders increases factorially with the number of tables involved. An 8 table join has 40,320 possible join orders. That rules out trial and error for all but the simplest queries.
It turns out that analyzing and diagramming according to Tow's method gives you a deep architectural understanding of the query and the problems that face you. It gives you a plan to which you can apply the tools of the trade, indexes, code optimization, etc.
This is a book that will be on the shelf of serious performance tuning professionals for as long as SQL is the language of data manipulation.
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11 of 11 people found the following review helpful:
5.0 out of 5 stars
A "Must Have" book for DBA's and SQL Developers, February 27, 2004
This review is from: SQL Tuning (Paperback)
For many years the process of SQL Tuning has been considered an "art". SQL tuning books written to date have presented guidelines and "things to try" but "SQL Tuning" by Dan Tow is different. This is the first book I have seen that presents a clear methodology to attack the problem in a scientific/mathematical way and includes a diagramming technique to visualize the components of a query that affect performance. Dan's book has gone a long way in helping to transform SQL tuning from an art to a science.
The first four chapters of the book cover some of the subjects that are found in other SQL tuning books, and focus on the important points without delving too deeply into database internals. The really "good stuff" is covered in chapters 5 through 10, which includes how to "draw" a query diagram, and the procedures to follow to derive an optimal join order. The problems/examples presented and resolved in these chapters help the reader get a start on understanding the methodology, which can then be applied to actual tuning problems as they are encountered.
So far I have applied this technique to about 20 tuning problems I have encountered on the job using the Oracle RDBMS. I still consider myself a relative novice in using the methodology, but for each of the 20 problems I have been able to significantly reduce elapsed time and resource consumption (gets/reads). Also, these results were achieved in a matter or hours, rather than days. The query diagram has even facilitated finding "missing joins" in some of the queries without having a knowledge of the particular application.
This book is a "must have" for DBA's and developers and I highly recommend it.
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