public inbox for [email protected]  

help / color / mirror / Atom feed

From: John Naylor <[email protected]>
To: Robert Haas <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: pg_plan_advice
Date: Tue, 4 Nov 2025 18:47:48 +0700
Message-ID: <CANWCAZaV57gYF09XFDODPPg=sRO-_HBcCZw4Kd=Ru21vXTq4rw@mail.gmail.com> (raw)
In-Reply-To: <CA+TgmoZ-Jh1T6QyWoCODMVQdhTUPYkaZjWztzP1En4=ZHoKPzw@mail.gmail.com>
References: <CA+TgmoZ-Jh1T6QyWoCODMVQdhTUPYkaZjWztzP1En4=ZHoKPzw@mail.gmail.com>

On Thu, Oct 30, 2025 at 9:00 PM Robert Haas <[email protected]> wrote:
> First, any form of user control over the
> planner tends to be a lightning rod for criticism around here. I've
> come to believe that's the wrong way of thinking about it: we can want
> to improve the planner over the long term and *also* want to have
> tools available to work around problems with it in the short term.

The most frustrating real-world incidents I've had were in the course
of customers planning a major version upgrade, or worse, after
upgrading and finding that a 5 minute query now takes 5 hours. I
mention this to emphasize that workarounds will be needed also to deal
with rare unintended effects that arise from our very attempts to
improve the planner.

> Further, we should not imagine that we're going to solve problems that
> have stumped other successful database projects any time in the
> foreseeable future; no product will ever get 100% of cases right, and
> you don't need to get to very obscure cases before other products
> throw up their hands just as we do.

Right.

> it seems to be super-useful for testing. We have
> a lot of regression test cases that try to coerce the planner to do a
> particular thing by manipulating enable_* GUCs, and I've spent a lot
> of time trying to do similar things by hand, either for regression
> test coverage or just private testing. This facility, even with all of
> the bugs and limitations that it currently has, is exponentially more
> powerful than frobbing enable_* GUCs. Once you get the hang of the
> advice mini-language, you can very quickly experiment with all sorts
> of plan shapes in ways that are currently very hard to do, and thereby
> find out how expensive the planner thinks those things are and which
> ones it thinks are even legal. So I see this as not only something
> that people might find useful for in production deployments, but also
> something that can potentially be really useful to advance PostgreSQL
> development.

That sounds very useful as well.

--
John Naylor
Amazon Web Services

view thread (133+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: pg_plan_advice
  In-Reply-To: <CANWCAZaV57gYF09XFDODPPg=sRO-_HBcCZw4Kd=Ru21vXTq4rw@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox