From: Tom Lane <tgl@sss.pgh.pa.us>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Alexander Korotkov <aekorotkov@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Planner issue on sorting joining of two tables with limit
Date: Fri, 07 May 2010 11:35:43 -0400
Message-ID: <13688.1273246543@sss.pgh.pa.us> (raw)
In-Reply-To: <4BE3EAF60200002500031399@gw.wicourts.gov>
References: <k2j2e2e4b141004251122u7adab639ve203afe7a486673f@mail.gmail.com>
<5252.1272300692@sss.pgh.pa.us>
<g2r2e2e4b141005030657vd6a0945fj9b9650bf515a189f@mail.gmail.com>
<l2z2e2e4b141005052354p9bd81643j866bc5ce5af3ada5@mail.gmail.com>
<4BE3EAF60200002500031399@gw.wicourts.gov>
"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
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, Kevin.Grittner@wicourts.gov, aekorotkov@gmail.com
Subject: Re: Planner issue on sorting joining of two tables with limit
In-Reply-To: <13688.1273246543@sss.pgh.pa.us>
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