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On the Topic of Programming 1

August 26, 2012 (Forward to the Next Post in the Series) As those of you who have read this blog’s About page probably know, my day to day job responsibilities involve a lot of activities that are not specific to Oracle Database performance tuning, or even remotely Oracle DBA type activities.  Those extra acttivites are part of what [...]

Parallel Parking – What is causing the Query to be Executed in Parallel?

July 31, 2012 I encountered an interesting OTN thread that caused me to stop and think for a couple of minutes.  The OP (original poster) in the OTN thread wondered why parallel execution was used for a query when the parallel degree for the table accessed by the query and its indexes were specified to have [...]

Book Review: Oracle Database 11gR2 Performance Tuning Cookbook (Part 2)

July 23, 2012 Oracle Database Performance Tuning Test Cases without Many “Why”, “When”, and “How Much” Filler Details (Back to the Previous Post in the Series) This blog article contains the review for the second half of the “Oracle Database 11gR2 Performance Tuning Cookbook” book.  It has been nearly five months since I posted [...]

Parallel Execution Challenge – It’s About Time

July 8, 2012 As I was reading a book, I saw a comment essentially stating that with multiple CPUs/cores, parallel execution will be faster than serial execution of the same query.  The book provided a test case - I decided to change around the test case a bit so that the results were a bit more fair, [...]

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

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 to, 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 [...]

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