Optimizer Costing 3 – What is Wrong with this Quote?

6 12 2010

December 6, 2010

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I recently reviewed the book “Oracle Tuning the Definitive Reference Second Edition”, and did not provide an in-depth technical review of the entire book.  This blog article series will dig into some of the pages that were not specifically included in the review.  What is wrong with the following quote from page 922 of the book?

Try a rule hint!

For testing unnecessary large table full table scans, try a rule hint (select /*+ RULE */ col1).  If the query uses the index with a rule hint, you have an issue with the CBO.”

What, if anything, is wrong with the above quote from the book?

The point of blog articles like this one is not to insult authors who have spent thousands of hours carefully constructing an accurate and helpful book, but instead to suggest that readers investigate when something stated does not exactly match what one believes to be true.  It could be that the author “took a long walk down a short pier”, or that the author is revealing accurate information which simply cannot be found through other resources (and may in the process be directly contradicting information sources you have used in the past).  If you do not investigate in such cases, you may lose an important opportunity to learn something that could prove to be extremely valuable.

As I stated in a comment in the earlier blog article, I would like to clarify that my review on the Amazon site is not intended to suggest that people should not buy the book. As the publisher’s website states that the book is written for senior Oracle DBAs, I suggest that senior DBAs, Oracle Certified Masters, and other people who are able to research the book’s contents *should* buy the book and post reviews of the book that highlight specific content of the book indicating whether or not that content is correctly stated. Such feedback will be a benefit to the Oracle community, and could help to improve Oracle Database books that are published in the future. I think that we need to keep a positive outlook in order to see things improve.

Other pages found during a Google search of the phrase:

Related Oracle Database documentation:





Optimizer Costing 2 – What is Wrong with this Quote?

6 12 2010

December 6, 2010

(Back to the Previous Post in the Series) (Forward to the Next Post in the Series)

I recently reviewed the book “Oracle Tuning the Definitive Reference Second Edition”, and did not provide an in-depth technical review of the entire book.  This blog article series will dig into some of the pages that were not specifically included in the review.  What is wrong with the following quote from page 527 of the book (this is an atypically long quote – the context would be lost if either of the two paragraphs were removed):

“In general, the Oracle CBO is unaware of buffer details, except when the optimizer_index_caching parameter is set where using multiple data buffers will not impact SQL execution plans.  When data using the new cpu_cost reported metric, the Oracle SQL optimizer builds the SQL plan decision tree based on the execution plan that will have the lowest estimated CPU cost.  For example, if a 32k data buffer is implemented for the index tablespace, the DBA can ensure that the indexes are cached for optimal performance and minimal logical I/O in range scans.

For example, if a database has 50 gigabytes of index space, a 60-gigabyte db_32k_cache_size can be defined and then the optimizer_index_caching parameter can be set to 100, telling the SQL optimizer that all of the Oracle indexes reside in RAM.  When Oracle makes the index versus table scan decision, knowing that the index nodes are in RAM will greatly influence the optimizer because the CBO knows that a logical I/O is often 100 times faster than a physical read.”

What, if anything, is wrong with the above quote from the book?

The point of blog articles like this one is not to insult authors who have spent thousands of hours carefully constructing an accurate and helpful book, but instead to suggest that readers investigate when something stated does not exactly match what one believes to be true.  It could be that the author “took a long walk down a short pier”, or that the author is revealing accurate information which simply cannot be found through other resources (and may in the process be directly contradicting information sources you have used in the past).  If you do not investigate in such cases, you may lose an important opportunity to learn something that could prove to be extremely valuable.

As I stated in a comment in the earlier blog article, I would like to clarify that my review on the Amazon site is not intended to suggest that people should not buy the book. As the publisher’s website states that the book is written for senior Oracle DBAs, I suggest that senior DBAs, Oracle Certified Masters, and other people who are able to research the book’s contents *should* buy the book and post reviews of the book that highlight specific content of the book indicating whether or not that content is correctly stated. Such feedback will be a benefit to the Oracle community, and could help to improve Oracle Database books that are published in the future. I think that we need to keep a positive outlook in order to see things improve.

A Google book search indicates that a slightly modified version of the statement appeared in a couple of  other books:

Other pages found during a Google search of the phrase:

  • dba-oracle.com/oracle_tips_multiple_blocksizes.htm
  • rampant-books.com/t_oracle_improve_sql_execution_speed.htm

Related Oracle Database documentation:








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