Re: Planner issue on sorting joining of two tables with limit - Mailing list pgsql-performance

From Tom Lane
Subject Re: Planner issue on sorting joining of two tables with limit
Date
Msg-id 13688.1273246543@sss.pgh.pa.us
Whole thread Raw
In response to Re: Planner issue on sorting joining of two tables with limit  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
Responses Re: Planner issue on sorting joining of two tables with limit  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-performance
"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> Alexander Korotkov <aekorotkov@gmail.com> wrote:
>>> I just don't find why it is coincidence. I think that such plan
>>> will always produce result ordered by two columns, because such
>>> nested index scan always produce this result.

> Assuming a nested index scan, or any particular plan, is unwise.

I think he's proposing that the planner should recognize that a plan
of this type produces a result sorted by the additional index columns.
I'm not convinced either that the sortedness property really holds,
or that it would be worth the extra planning effort to check for;
but it's not a fundamentally misguided proposal.

            regards, tom lane

pgsql-performance by date:

Previous
From: "Kevin Grittner"
Date:
Subject: Re: Planner issue on sorting joining of two tables with limit
Next
From: Josh Berkus
Date:
Subject: Re: partioning tips?