I Didn’t Know That 4 – What is Wrong with this Quote?

12 12 2010

December 12, 2010

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

In the interest of interesting quotes, a quote that I found in the “Oracle Tuning the Definitive Reference Second Edition” book on page 987:

Row ordering matters!
In some systems where a table is always accessed by the same key sequence, re-ordering the table into the same order as the queries can dramatically reduce I/O and improve SQL performance.

When reorganizing tables to improve SQL performance, keep this in-mind:

  • Only tables that experience multi-block reads (full-table scans) may see an appreciable SQL performance benefit.
  • Some shops will use sorted hash cluster tables to maintain row sequence order (in the same order as the most common indexed retrieval), and you can reorganize a table with an ‘order by’ clause to make the rows in the same sequence as the index.

But it’s not just tables that require periodic maintenance, it’s also indexes.”

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

—————–

While my review of the book only provides an in-depth technical review of the first 200 pages of the book, this blog article series will dig into some of the pages that were not specifically included in the review.

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.

Other pages found during a Google search of the phrase:

  • remote-dba.net/t_oracle_net_reorganize_tables.htm
  • dba-oracle.com/art_disk_io.htm
  • dba-oracle.com/t_table_row_resequencing.htm
  • dba-oracle.com/t_create_table_select_ctas.htm







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