| From: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
|---|---|
| To: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Nikita Glukhov <n(dot)gluhov(at)postgrespro(dot)ru>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Fetter <david(at)fetter(dot)org>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Oleksandr Shulgin <oleksandr(dot)shulgin(at)zalando(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Oleg Bartunov <obartunov(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] [PATCH] Generic type subscripting |
| Date: | 2020-12-02 19:20:10 |
| Message-ID: | 20201202192010.GI24052@telsasoft.com |
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| Thread: | |
| Lists: | pgsql-hackers |
On Wed, Dec 02, 2020 at 08:18:08PM +0100, Dmitry Dolgov wrote:
> > On Wed, Dec 02, 2020 at 12:58:51PM -0500, Tom Lane wrote:
> > So ... one of the things that's been worrying me about this patch
> > from day one is whether it would create a noticeable performance
> > penalty for existing use-cases. I did a small amount of experimentation
> > about that with the v35 patchset, and it didn't take long at all to
> > find that this:
> > --- cut ---
> >
> > is about 15% slower with the patch than with HEAD. I'm not sure
> > what an acceptable penalty might be, but 15% is certainly not it.
> >
> > I'm also not quite sure where the cost is going. It looks like
> > 0001+0002 aren't doing much to the executor except introducing
> > one level of subroutine call, which doesn't seem like it'd account
> > for that.
>
> I've tried to reproduce that, but get ~2-4% slowdown (with a pinned
> backend, no turbo etc). Are there any special steps I've probably
> missed? At the same time, I remember had conducted this sort of tests
> before when you and others raised the performance degradation question
> and the main part of the patch was already more or less stable. From
> what I remember the numbers back then were also rather small.
Are you comparing with casserts (and therefor MEMORY_CONTEXT_CHECKING) disabled?
--
Justin
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