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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: James Coleman <jtc331@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Rafia Sabih <rafia.pghackers@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: Shaun Thomas <shaun.thomas@2ndquadrant.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Cc: Andreas Karlsson <andreas@proxel.se>
Subject: Re: [PATCH] Incremental sort (was: PoC: Partial sort)
Date: Tue, 31 Mar 2020 18:35:32 -0400
Message-ID: <2608.1585694132@sss.pgh.pa.us> (raw)
In-Reply-To: <20200331215340.bbbrccbehmjb7dbx@development>
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	<20200329031437.yvhogo25wdijwpqd@development>
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	<20200330014442.chqnwfmelm3ejsgr@development>
	<CAAaqYe__vp0QQHgUfiVe+NrcMpECfQgZO8iu2CEwVOcBgA+S0Q@mail.gmail.com>
	<20200330122426.wjdfpqiatv4ybui7@development>
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	<20200331011407.vwz3ektatgqyi6vy@development>
	<CAAaqYe8M-r4esHOg_46w3ojeUEB7KGZ4j2GAi6rLv0B9bHoiPg@mail.gmail.com>
	<20200331215340.bbbrccbehmjb7dbx@development>

Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> In general, I think it'd be naive that we can make planner smarter with
> no extra overhead spent on planning, and we can never accept patches
> adding even tiny overhead. With that approach we'd probably end up with
> a trivial planner that generates just a single query plan, because
> that's going to be the fastest planner. A realistic approach needs to
> consider both the planning and execution phase, and benefits of this
> patch seem to be clear - if you have queries that do benefit from it.

I think that's kind of attacking a straw man, though.  The thing that
people push back on, or should push back on IMO, is when a proposed
patch adds significant slowdown to queries that it has no or very little
hope of improving.  The trick is to do expensive stuff only when
there's a good chance of getting a better plan out of it.

			regards, tom lane





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