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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Mladen Gogala <mladen.gogala@vmsinfo.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: anti-join chosen even when slower than old plan
Date: Thu, 11 Nov 2010 14:17:00 -0500
Message-ID: <19475.1289503020@sss.pgh.pa.us> (raw)
In-Reply-To: <AANLkTi=t7Oe9bSjK_apn_V2jMGu5Hp3b4iix4te2WER9@mail.gmail.com>
References: <4CD9663502000025000374B1@gw.wicourts.gov>
	<20961.1289347680@sss.pgh.pa.us>
	<4CDA62C60200002500037512@gw.wicourts.gov>
	<AANLkTi=eNXKEBo5dXJDd4+aHhfmkibH++fqjj12+DA3o@mail.gmail.com>
	<4CDACBBF020000250003755B@gw.wicourts.gov>
	<4CDB7BAA.7020506@vmsinfo.com>
	<4CDBB0A40200002500037571@gw.wicourts.gov>
	<AANLkTi=dzhRTTNm1LkyNCAC5+PWbp1jWtKFh4T1Bu4nj@mail.gmail.com>
	<18450.1289499783@sss.pgh.pa.us>
	<AANLkTi=t7Oe9bSjK_apn_V2jMGu5Hp3b4iix4te2WER9@mail.gmail.com>

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Nov 11, 2010 at 1:23 PM, Tom Lane <tgl@sss.pgh.pa.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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