Re: [PATCH] Incremental sort (was: PoC: Partial sort)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: James Coleman <jtc331(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Shaun Thomas <shaun(dot)thomas(at)2ndquadrant(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andreas Karlsson <andreas(at)proxel(dot)se>
Subject: Re: [PATCH] Incremental sort (was: PoC: Partial sort)
Date: 2020-03-31 22:35:32
Message-ID: 2608.1585694132@sss.pgh.pa.us
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Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)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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