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Histograms – What is Wrong with this Quote?

July 4, 2012 It has been several months since I posted my review of the first half of the “Oracle Database 11gR2 Performance Tuning Cookbook” book.  I had planned to post the review for the second half of the book a couple of weeks later, however four months have passed by since that time, and the second [...]

Different Execution Plans when Converting SQL from SELECT to UPDATE … IN SELECT, ROWNUM Related Bug in 11.2.0.2

June 28, 2012 (Modified June 28, 2012) Sometimes it is possible to build a very effective test case to reproduce a particular problem.  Sometimes the test case drifts a bit offtrack, in the process revealing other information that is not directly related to the original problem that the test case attempted to simulate.  You will [...]

Why is a Full Table Scan Selected – Will the Execution Plan Provide a Clue?

June 20, 2012 I have not had much time to respond in OTN threads recently, although I do still occasionally read threads on the forum.  I was a little surprised by one of the late responses in one of the recent threads, where one of the responders suggested actually testing the problem with the assistance of [...]

SQL Challenges

June 14, 2012 Dominic Delmolino put together a very interesting challenge.  The challenge is to produce something called a Pascal matrix using Oracle Database… more specifically, just SQL.  I had a vague recollection of Pascal matrixes when I read Dominic’s challenge.  Basically, the goal is to create a matrix similar to the following: The rule [...]

Execution Plan Changes when the OPTIMIZER_FEATURES_ENABLED Parameter is Changed, But Why?

May 30, 2012 A question appeared on the OTN Database forums yesterday that has yet to receive an answer.  The question was essentially, why did the execution plan change when the OPTIMIZER_FEATURES_ENABLED parameter was adjusted from 11.2.0.2 to 11.1.0.7, and why did the execution performance improve as a result of making the change?  A DBMS_XPLAN [...]

TKPROF Elapsed Time Challenge – the Elapsed Time is Half of the Wait Event Time

May 20, 2012 An interesting quirk was recently brought to my attention by Mich Talebzadeh.  He generated a 10046 trace at level 8 for a session, executed some SQL statements, disabled the trace, and then processed the resulting trace file with TKPROF.  His TKPROF output included the following: UPDATE TESTWRITES SET PADDING1 = RPAD('y',4000,'y') WHERE [...]

On the Topic of Technology… 4

May 7, 2012 (Back to the Previous Post in the Series) Today’s blog article has an unusual tie in with Oracle. The last couple of weeks I have been experimenting with video technology.  Computer related video capabilities have certainly changed over the years.  In 1996 I purchased a Sony Handicam and a Video Snappy.  The [...]

Brain Teaser: 10046 Extended SQL Trace Shows a FETCH Call with c=306350000, e=299174653, p=0, cr=22298 – How is that Possible?

April 26, 2012 Last week I posted a popular article that questioned the effectiveness of showing a job candidate a raw 10046 trace file that was captured at level 12, asking the job candidate to evaluate whether or not the SQL statement in the 10046 trace is efficient.  Many of the commenters suggested that the [...]

Temporary Tablespace Storage Parameters – What is Wrong with this Quote

April 22, 2012 (Modified April 24, 2012) I had intended to finish assembling the second half of the “Oracle Database 11gR2 Performance Tuning Cookbook” book review, however my free time that may be dedicated to book reviews has been a bit limited lately (I have a review of another book started, but left untouched for [...]

Extents of an Oracle Database DBA’s Knowledge Base

April 18, 2012 I saw an interesting thread on the OTN forums this morning that forced me to stop and think about several items.  The thread contains a question posed during a recent job interview – one of the best questions that I have seen (dare I say, better than one I might have crafted myself).  [...]

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