Horton

Re: FETCH FIRST clause WITH TIES option

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Surafel Temesgen <surafel3000@gmail.com>, David Steele <david@pgmasters.net>, Michael Paquier <michael@paquier.xyz>, Robert Haas <robertmhaas@gmail.com>, andrew@tao11.riddles.org.uk, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2019-04-03T19:08:05Z
Lists: pgsql-hackers 
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

Commits

  1. Support FETCH FIRST WITH TIES