APress – Expert Oracle DB Arch by Tom Kyte

I have a confession to make. I haven’t read an Oracle book cover-to-cover in almost three years. Sure I skim through the latest titles for what I need and of course check out documentation of the latest releases. That’s what good docs provide, quick reference when you need to check syntax, or details of a particular parameter, or feature, but have you ever read some documentation, sift through a paragraph, page or two, and say to yourself, that’s great, but what about this situation I have right now? Unfortunately documentation doesn’t always

speak to your real everyday needs. It is excellent for reference, but doesn’t

have a lot of real-world test cases, and practical usage examples. That’s where Tom Kyte’s new book comes in, and boy is it a killer.

I’ve read Tom’s books before, and always enjoyed them. But his new APress title really stands out as an achievement. Page after page and chapter after chapter he uses straightforward examples pasted right from the SQL*Plus prompt to illustrate, demonstrate, and illuminate concepts that he is explaining. It is this practical hands on, relentless approach that makes this book 700 pages of goodness.

Already an expert at Oracle? You’ll become more of one after reading this book. With reviewers like Jonathan Lewis I expected this book to be good from the outset I have to admit. But each chapter delves into a bit more depth around subjects that are central to Oracle programming and administration.

No SCREEN SHOTS!

One of the things I loved about this book most of all is its complete lack of screenshots! But how does one illustrate a concept then, you might ask? These days with graphical interfaces becoming more and more popular even among technical folks, I run into the question of the command line over an over again. How can you be doing sophisticated database administration of the latest servers running Oracle with the command line? Or another question I often get is, can you really do everything with the command line? The answer to both is a resounding yes, in fact you can do much more with the command line. Luckily for us, Tom is of this school too, and page after page of his book are full of real examples and commands that you can try for yourself, with specific instructions on

setting up the environment, using statistics gathering packages, and so on. In an era of computing where GUIs seem to reign like magazines over the best literature of the day, it is refreshing to see some of the best and most technical minds around Oracle still advocate the best tool, command line as the interface

of choice. In fact it is the command line examples, and happily the complete lack of screenshots that indeed makes this book a jewel of a find.

Audience

As a DBA you might wonder why I’m talking so highly of a book more focused towards developers. There are a couple of reasons. First this book is about the Oracle architecture, as it pertains to developers. In order for developers to best take advantage of the enterprise investment in Oracle *** they need to thoroughly understand the architecture, how specific features operate, which features are appropriate, and how to optimize their code for best interaction with them. Of course a DBA who is trying to keep a database operating in tip top shape needs to be aware of when developers are not best using Oracle, to identify,

and bring attention to bottlenecks, and problem areas in the application. Second, it is often a DBAs job to tune an existing database, and the very largest benefits come from tuning application SQL. For instance if a developer has chosen to use a bitmap index on an INSERT/UPDATE intensive table, they’re in for serious problems. Or if a developer forgot to index a foreign key column. This book directly spearheads those types of questions, and when necessary does mention a thing or two of direct importance to DBAs as well.

Highlights

Chapter 2 has an excellent example of creating an Oracle database. You simply write one line to your init.ora “db_name=sean” for example, and then from the SQL> prompt issues “startup nomount” and then “create database”. Looking at the processes Oracle starts, and the files that are created can do wonders for your understanding of database, instance, and Oracle in general.

Chapter 3 covers files, files, and more files. Spfile replaces a text init.ora allowing parameters to be modified while an instance is running *AND* stored persistently. He covers redolog files, flashback logs, and change tracking file

s, as well as import/export dump files, and lastly datapump files.

Chapter 4 covers memory, and specifically some of the new auto-magic options, how they work, and what to watch out for.

Chapter 5 covers processes.

Chapter 6, 7, and 8 cover lock/latching, multiversioning, and transactions respectively. I mention them all here together because to me these chapters are the real meat of the book. And that’s coming from a vegetarian! Seriously these

topics are what I consider to be the most crucial to understanding Oracle, and modern databases in general, and the least understood. They are the darkest corners, but Tom illuminates them for us. You’ll learn about optimistic versus pessismistic locking, page level, row level, and block level locking in various modern databases such as SQLServer, Informix, Sybase, DB2 and Oracle. Note Oracle is by far in the lead in this department, never locking more than it needs to, which yields the best concurrency with few situations where users block each other. Readers never block, for instance, because of the way Oracle implements all of this. He mentions latch spinning, which Oracle does to avoid a context switch, that is more expensive, how to detect, and reduce this type of contention. You’ll learn about dirty reads, phantom reads, and non-repeatable reads, and about Oracle’s Read-committed versus Serializable modes. What’s more you’ll learn about the implications of these various models on your applications, and what type of assumptions you may have to unlearn if you’re coming from developing on another database to Oracle. If I were to make any criticism at all, I might mention that in this area Tom becomes ever so slightly preachy about Oracle’s superb implementation of minimal locking, and non-blocking reads. This is in large part due I’m sure to running into so many folks who are used to developing on databases which do indeed dumb you down *BECAUSE* of their implementation, encouraging bad habits with respect to transactions, and auto-commit for instance. One thing is for sure you will learn a heck of a lot from these three chapters, I know I did.

Chapter 9 Redo & Undo describes what each is, how to avoid checkpoint not complete and why you want to, how to *MEASURE* undo so as to reduce it, how to avoid log file waits (are you on RAID5, are your redologs on a buffered filesystem?), and what block cleanouts are.

Chapter 10 covers tables. After reading it I’d say the most important types are normal (HEAP), Index Organized, Temporary, and External Tables. Use ASSM where possible as it will save you in many ways, use DBMS_METADATA to reverse engineer objects you’ve created to get all the options, don’t use TEMP tables to avoid inline views, or complex joins, your performance will probably suffer, and how to handle LONG/LOB data in tables.

Chapter 11 covers indexes, topics ranging from height, compression count, DESC sorted, colocated data, bitmap indexes and why you don’t want them in OLTP data

bases, function based indexes and how they’re most useful for user defined functions, why indexing foreign keys is important, and choosing the leading edge of an index. Plus when to rebuild or coalesce and why.

Chapter 12 covers datatypes, why never to use CHAR, using the NLS features, the CAST function, the number datatypes and precision versus performance, raw_to_hex, date arithmatic, handling LOB data and why not to use LONG, BFILEs and the new UROWID.

Chapter 13 discusses partitioning. What I like is he starts the chapter with the caveat that partitioning is not the FAST=TRUE option. That says it all. For OLTP databases you will achieve higher availability, and ease of administration of large options, as well as possibly reduced contention on larger objects,

but it is NOT LIKELY that you will receive query performance improvements because of the nature of OLTP. With a datawarehouse, you can use partition elimination on queries that do range or full table scans which can speed up queries dramatically. He discusses range, list, hash, and composite partitioning, local indexing (prefixed & non-prefixed) and global indexing. Why datawarehouses tend to use local, and OLTP databases tend to use global indexes, and even how you

can rebuild your global indexes as you’re doing partition maintenance avoiding a costly rebuild of THE ENTIRE INDEX, and associated downtime. He also includes a great auditing example.

Chapter 14 covers parallel execution such as parallel dml, ddl, and so on. Here is where a book like Tom’s is invaluable, as he comes straight out with his opinions on a weighty topic. He says these features are most relevant to DBAs doing one-off maintenance and data loading operations. That is because even in

datawarehouses, todays environments often have many many users. The parallel features are designed to allow single session jobs to utilize the entire system resources. He explains that Oracle’s real sweet spot in this real is parallel

DDL, such as CREATE INDEX, CREATE TABLE AS SELECT, ALTER INDEX REBUILD, ALTER TABLE MOVE, and so on.

Chapter 15, the final chapter covers loading and unloading data. A significant portion of the chapter covers SQL*Loader for completeness, but he goes on to celebrate the wonders of external tables for loading data into Oracle. In particular there is an option in SQL*Loader to generate the CREATE statement for an

external table that does the SAME load! This is great stuff. External tables provide advantages over SQL*Loader in almost every way, except perhaps loading over a network, concurrent user access, and handling LOB data. External tables can use complex where clauses, merge data, do fast code lookups, insert into multiple tables, and finally provide a simpler learning curve.

Conclusions

Yum. If you love Oracle, you’ll want to read this book. If you need to know more about Oracle say, for your job, that’s another reason you might read this book. Oracle is fascinating technology, and Tom’s passion for understanding every last bit of it makes this book both a necessary read, and a very gratifying

one.

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