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From: David Rowley <[email protected]>
To: Tom Lane <[email protected]>
Cc: Nathan Bossart <[email protected]>
Cc: [email protected]
Subject: Re: pgsql: Add vacuum_truncate configuration parameter.
Date: Fri, 21 Mar 2025 12:07:00 +1300
Message-ID: <CAApHDvo9E+imdCrOjhx00unxxDYox=7fr2+ATfyEw86iRwy3AA@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

On Fri, 21 Mar 2025 at 04:30, Tom Lane <[email protected]> wrote:
>
> Nathan Bossart <[email protected]> writes:
> > Since there's presently no way to determine whether a Boolean
> > storage parameter is explicitly set or has just picked up the
> > default value, this commit also introduces an isset_offset member
> > to relopt_parse_elt.
>
> Uh, what?  Why is it a good idea to distinguish those states?
> Seems like that risks some very surprising behavior, ie if the
> default is "true", why shouldn't that act exactly like an
> explicit setting of "true"?

I was thinking about this yesterday as the topic of a
user-configurable options for truncation threshold came up in [1]. I
find it a bit annoying the boolean vacuum_truncate reloption was added
(a few years ago) as we could have instead added a more flexible
truncate_scale_factor that could be set to -1 to disable truncation.
Maybe it's too late now as reloptions are not easy to remove. Adding
this GUC now does put us a bit further down the path of the boolean
option.

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