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Re: anti-join chosen even when slower than old plan

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: anti-join chosen even when slower than old plan
Date: 2010-11-11 19:17:00
Message-ID: 19475.1289503020@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Nov 11, 2010 at 1:23 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I do think that something based around a settable-per-table caching
>> percentage might be a reasonable way to proceed. But the devil is in
>> the details, and we don't have those yet.

> I think one of the larger devils in the details is deciding how to
> estimate the assumed caching percentage when the user hasn't specified
> one.

I was imagining something very similar to the handling of seq_page_cost,
ie, there's a GUC controlling the system-wide default and then you can
override that per-table.  But the real question is whether per-table
is a useful granularity to control it at.  See my later message.

			regards, tom lane

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