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help / color / mirror / Atom feedFrom: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Surafel Temesgen <surafel3000@gmail.com>
Cc: David Steele <david@pgmasters.net>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: andrew@tao11.riddles.org.uk, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: FETCH FIRST clause WITH TIES option
Date: Wed, 03 Apr 2019 15:08:05 -0400
Message-ID: <32413.1554318485@sss.pgh.pa.us> (raw)
In-Reply-To: <20190403190257.44fxttkpo4yopp3l@development>
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<20190403190257.44fxttkpo4yopp3l@development>
Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> I've tried to fix the merge conflict (essentially by moving some of the
> code to adjust_limit_rows_costs(), but I'm wondering if the code added to
> create_limit_path is actually correct
> ...
> Firstly, this seriously needs some comment explaining why we do this.
I've not looked at this patch, but TBH I wonder why it is touching
planner rowcount estimation at all. I find it doubtful either that
a correction for WITH TIES would be significant in most use-cases,
or that we could estimate it accurately if it was significant.
It certainly doesn't seem like something that needs to be messed
with in v1 of the feature.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, tomas.vondra@2ndquadrant.com, surafel3000@gmail.com, david@pgmasters.net, michael@paquier.xyz, robertmhaas@gmail.com
Subject: Re: FETCH FIRST clause WITH TIES option
In-Reply-To: <32413.1554318485@sss.pgh.pa.us>
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