From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Bruce Momjian <pgman(at)candle(dot)pha(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 16:34:49 |
Message-ID: | 18684.1137774889@sss.pgh.pa.us |
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Lists: | pgsql-performance |
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
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