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Re: PlaceHolderVars versus join ordering

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: PlaceHolderVars versus join ordering
Date: 2010-09-28 01:27:27
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Sep 27, 2010 at 1:15 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> This is a larger change than I would prefer to back-patch, but the only
>> less-invasive alternative I can see is to lobotomize the PlaceHolderVar
>> mechanism entirely by reverting to 8.3-style logic wherein we prevented
>> pullup of sub-selects that would require introduction of placeholders.
>> That would undo a significant optimization feature of 8.4, one that
>> I believe we're now relying on for reasonable performance of some system
>> views.
>> Thoughts, better ideas?

> Personally, I would rather back-patch a more invasive bug fix than a
> performance regression.

Yeah, me too.  Attached is a draft patch against HEAD --- comments?

			regards, tom lane

Attachment: placeholder-delay-1.patch
Description: text/x-patch (27.4 KB)

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