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Re: Extremely irregular query performance

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Jean-Philippe Côté <jean-philippe(dot)cote(at)crt(dot)umontreal(dot)ca>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Extremely irregular query performance
Date: 2006-01-20 16:42:11
Message-ID: 200601201642.k0KGgBS23410@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Done, and paragraph added to 8.1.X.  (7.3 mention retained for 8.1.X.)

---------------------------------------------------------------------------

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> >     <para>
> > !    Genetic query optimization (<acronym>GEQO</acronym>) randomly 
> > !    tests execution plans.  Therefore, when the number of tables 
> > !    exceeds <varname>geqo</> and genetic query optimization is in use,
> > !    the execution plan will change each time the statement is executed.
> >     </para>
> 
> geqo_threshold, please --- geqo is a boolean.
> 
> Possibly better wording:  Therefore, when the number of tables exceeds
> geqo_threshold causing genetic query optimization to be used, the
> execution plan is likely to change each time the statement is executed.
> 
> 			regards, tom lane
> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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