Le mar. 12 nov. 2024 à 16:21, Robert Haas <robertmh...@gmail.com> a écrit :
> On Mon, Nov 11, 2024 at 3:59 PM Guillaume Lelarge
> <guilla...@lelarge.info> wrote:
> > Agreed. Having an "EXPLAIN (ALL)" would be a great addition. I could
> tell a customer to do an "EXPLAIN (ALL)", rather than first asking the
> PostgreSQL release installed on the server and after that, giving the
> correct options for EXPLAIN.
>
> I realize that you're probably going to hate my guts -- or hate them
> even more than you do already -- but I doubt that a proposal to add
> EXPLAIN (ALL) will go anywhere.
I don't hate your guts :) and...
> The definitional problem is that it is
> not clear what to do with non-Boolean valued options, such as
> SERIALIZE. People who think that we were wrong not to make SERIALIZE
> TEXT the default in v17 will argue that EXPLAIN (ALL) should turn it
> on; after all, the backward-compatibility argument carries no water in
> that case. But people who do not like the behavior of SERIALIZE TEXT
> will not be happy about that. They might directly make that argument,
> or they might instead make the argument that ALL should do nothing
> about a non-Boolean valued option. But that position is really quite
> difficult to justify. Let's suppose that the current BUFFERS option,
> which is Boolean, got replaced with BUFFERS { detailed | on | off }.
> Well, then, by the principle that ALL only affects Boolean-valued
> options, it's no longer included in EXPLAIN (ALL). Nobody will be
> happy with that. Practically speaking, I think it will be very
> difficult to get agreement on what EXPLAIN (ALL) should do, and I
> think it is unlikely that anything will get committed no matter how
> much time we spend arguing about it.
>
>
... I kinda agree with you. It would have been nice to have an "EXPLAIN
(ALL)" but I completely understand the issue.
> But I think we would get most of the same benefit from just doing what
> David Rowley proposed and turning on EXPLAIN (BUFFERS) by default. I'd
> suggest that we decide that, without ANALYZE, the option would not do
> anything; that is already how TIMING works. So this would be a very
> small patch and would probably get a lot of support from a lot of
> people. It also wouldn't require users to change their habits or learn
> any new syntax -- they could just keep typing EXPLAIN ANALYZE or
> EXPLAIN ANALYZE VERBOSE and all would be well.
>
>
That would be a nice enhancement.
> And the same principle could be applied to other EXPLAIN options if
> there is sufficient consensus. We could default to WAL ON, SERIALIZE
> TEXT, and MEMORY ON, if we wanted to do that. However, the more we try
> to change at once, the less likely it is that anything will happen at
> all. For example, I personally believe that EXPLAIN (MEMORY) should be
> ripped out of the server as both badly-named and mostly useless, so
> I'm not going to vote in favor of turning it on by default; and I
> wouldn't vote for enabling WAL by default because I have no experience
> with it to suggest that it's routinely valuable and thus worth the
> overhead. I would vote for SERIALIZE TEXT because I've seen that cause
> gross distortion of EXPLAIN ANALYZE results on many occasions. But the
> point is that other people will vote differently, so tying all the
> proposals together just increases the chances of agreeing on nothing
> at all.
>
>
Agreed.
> So to recap: everyone is free to propose whatever they like, and I am
> not in charge here, but if you want to get something committed, the
> proposal which I think has the highest chance of success is: propose
> to make BUFFERS ON the default (but a noop without ANALYZE, similar to
> how TIMING already works).
>
>
Sounds like a plan.
Thanks.
--
Guillaume.
