Oracle Scratchpad

July 27, 2014

Parallel Plans

Filed under: Execution plans,Oracle,Parallel Execution — Jonathan Lewis @ 8:39 pm BST Jul 27,2014

I’ve popped this note to the top of the stack (and had to delete and refresh all the related pingbacks on my blog) because I’ve added an index to Randolf Geist’s series on parallel execution skew, and included a reference his recent update to the XPLAN_ASH utility.

This is the directory for a short series I wrote discussing how to interpret parallel execution plans in newer versions of Oracle.

For other aspects of parallel execution, here are links to several articles by Randolf Geist, published on his own blog or on Oracle’s Technet:

One of the awkward problems you can encounter with parallel execution is data skew – which has the potential to make just one slave in a set do (almost) all the work hence reducing the performance to something close to serial execution times.  Randolf has written a series of articles on Parallel Skew that has been published by AllthingsOracle over the last few months.

And his summary posting listing the 5 articles above, but also including a set of videos on the topic.



  1. Just added a link to Randolf’s own summary posting for parallel skew – which includes links to a set of videos on the topic.

    Comment by Jonathan Lewis — August 4, 2014 @ 1:06 am BST Aug 4,2014 | Reply

  2. […] operation, which means they can report the wrong order. [Update 3/Jan/2015: Here’s a link to a catalogue of articles that Randolf Geist and I have written about parallel execution plans showing (a.o.) the failure of […]

    Pingback by Interesting Plan | Oracle Scratchpad — January 3, 2015 @ 10:25 am BST Jan 3,2015 | Reply

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