DB_BLOCK_SIZE and DB_FILE_MULTIBLOCK_READ_COUNT 3 – What is Wrong with this Quote?

4 12 2010

December 4, 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.  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

With that said, what is wrong with the following quote from page 719 of the book (please ignore the error in the SQL statement found on that page for the moment)?

“Four factors synchronize to help the CBO choose whether or use an index or a full-table scan:

7.  The selectivity of a column value
8.  The db_block_size
9.  The avg_row_len
10. The cardinality

An index scan is usually faster if a data column has high selectivity and a low clustering_factor as shown in Figure 15.8.”

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.

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:


For some reason, the following quote seems to come to mind:

“Fool me once, shame on me.  Fool me twice, shame on you.” (reference)