As Published In
Oracle Magazine
May/June 2009

From Our Readers


Your corrections, your opinions, and your requests: Here’s your forum for telling us what’s right and wrong in each issue of Oracle Magazine, and for letting us know what you want to read.

Level with Me

On Dynamic Sampling”(Oracle Magazine, January/February 2009) contains a portion of the Performance Tuning Guide that explains the differences between dynamic sampling levels. Here’s part of it (emphasis mine):

Level 2: Apply dynamic sampling to all unanalyzed tables . The number of blocks sampled is two times the default number of dynamic sampling blocks.
Level 3: Apply dynamic sampling to all tables that meet Level 2 criteria, plus all tables for which . . . My question: If level 2 performs dynamic sampling on all unanalyzed tables, what other tables can levels 3 and up analyze? Do they gather statistics on tables that already have statistics? I doubt that’s the case, but what other tables are there?
Paul Muller
paul.muller@thestructuregroup.com

Tom Kyte replies: Level 3 samples data in a way to validate “guesses” the optimizer might otherwise have to make. It gathers statistics that are specific to the query in question. In the online version of that column, see the section “When the Optimizer Guesses” for an example of what I mean. That example is run in Oracle Database 11g, which has dynamic sampling set to 2. When I tell it to use level 3, it samples the table even though it has statistics on it—but it’s sampling to figure out what the WHERE clause will really do. It is the flag1/flag2 example and was designed to demonstrate the difference between levels 2 and 3.

Getting Started

As a regular reader of Oracle Magazine , I request that you include introductory articles for Oracle beginners on topics such as installation, programming, networking, and creating a database.
Chinedu Ikwumezie
chembers007@yahoo.com

More Business Intelligence

I am a regular reader of Oracle Magazine and have read almost all the issues to date for the past three years.

In spite of popular business intelligence and data warehousing technologies offered by Oracle, there isn’t a section in Oracle Magazine for these types of technologies, as there is for PL/SQL, Oracle SQL Developer, and so on.

I would be interested in a section for business intelligence and data warehousing.
Vikram Rathour
rathour.vikram@gmail.com

Reality Check

The article “Integrating Applications” (by David A. Kelly, March/April 2009) is very interesting and resonates in today’s business environments. Most enterprises are using several standalone applications, and the article highlights that reality.
P. Ramnath
ramnath.p@gts-india.com  

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Kindle-ing Interest

Do you currently have plans to publish Oracle Magazine (and any other Oracle news content) to Amazon’s Kindle?
Jason Bell
jbell@dealflownetworks.com

The editors reply: We are evaluating the distribution of Oracle Magazine for the Kindle 2. We currently publish Oracle Magazine in print and multiple electronic formats, including one for the iPhone. The digital edition of Oracle Magazine offers a custom online format with hyperlinks and a PDF format for download and offline viewing. Subscribers can choose to receive the print or digital edition of the magazine by indicating their preference for print or digital in the online subscription form . Subscribers and nonsubscribers can view Oracle Magazine in HTML format at oracle.com/oraclemagazine .



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