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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Subject: Re: WIP: Faster Expression Processing v4
Date: Wed, 15 Mar 2017 15:41:22 -0400
Message-ID: <3401.1489606882@sss.pgh.pa.us> (raw)
In-Reply-To: <855716B2-7522-4C79-A50E-2EB8E609764F@anarazel.de>
References: <20161206034955.bh33paeralxbtluv@alap3.anarazel.de>
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	<2090fd00-4dec-7b42-f700-64308958504c@2ndquadrant.com>
	<20170313080351.4g5oubxcj4xj5y7t@alap3.anarazel.de>
	<fcdaa51b-e905-72e0-39dd-5e22f535a253@2ndquadrant.com>
	<20170314065259.ffef4tfhgbsaieoe@alap3.anarazel.de>
	<69b7bb0e-8dab-3d39-1a89-3c6ab6409f64@iki.fi>
	<20170314224706.nxvtapenky6eom3z@alap3.anarazel.de>
	<3086.1489606408@sss.pgh.pa.us>
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Andres Freund <andres@anarazel.de> writes:
> On March 15, 2017 12:33:28 PM PDT, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> So for my money, you should drop 0002 altogether and just have 0004
>> remove get_last_attnums() from execUtils.c and stick it into
>> execExpr.c.  I suppose you still need the LastAttnumInfo API change
>> so as to decouple it from ProjectionInfo, but that's minor.

> I think it's quite useful in other places too, we do repeated slot-getattrs in a bunch of places in the executor, and it's noticeable performance wise. 

Color me dubious.  Which specific other places have you got in mind, and
do they have expression trees at hand that would tell them which columns
they really need to pull out?

			regards, tom lane


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