Re: Why could GEQO produce plans with lower costs than the standard_join_search?

From: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
To: "Finnerty\, Jim" <jfinnert(at)amazon(dot)com>
Cc: Donald Dong <xdong(at)csumb(dot)edu>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Why could GEQO produce plans with lower costs than the standard_join_search?
Date: 2019-05-23 08:57:18
Message-ID: 871s0pd03k.fsf@news-spur.riddles.org.uk
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>>>>> "Finnerty" == Finnerty, Jim <jfinnert(at)amazon(dot)com> writes:

Finnerty> planstate-> total_cost cheapest_total_path
Finnerty> GEQO 54190.13 54239.03
Finnerty> STD 54179.02 54273.73

These differences aren't significant - the standard join search has a
"fuzz factor" built into it, such that paths have to be more than 1%
better in cost in order to actually be considered as being better than
an existing path.

--
Andrew (irc:RhodiumToad)

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