Re: GEQO and join_collapse_limit correlation

From: Juan José Santamaría Flecha <juanjo(dot)santamaria(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: GEQO and join_collapse_limit correlation
Date: 2018-01-06 11:31:51
Message-ID: CAC+AXB0rKyPPCbnT_oq2LkKTdN+5bPRZ2gEjArqwVutaNY2=bw@mail.gmail.com
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Hi,

GEQO's only function, basically, is to search for the join order to use.
> If you're constraining the join order completely with
> join_collapse_limit=1 then forcing the GEQO path to be taken would just
> add pointless overhead. (If it does anything at all ... I don't remember
> the logic exactly but we might be bright enough not to bother with GEQO in
> such a situation, regardless of geqo_threshold.)
>

Got it. Thanks a lot.

Regards,

Juan José Santamaría

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