Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions

From: David Fetter <david(at)fetter(dot)org>
To: Ian Barwick <ian(dot)barwick(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Stephen Frost <sfrost(at)snowman(dot)net>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions
Date: 2019-08-05 16:22:03
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On Mon, Aug 05, 2019 at 03:52:07PM +0900, Ian Barwick wrote:
> On 8/4/19 1:59 AM, Tom Lane wrote:> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> >> On Fri, Aug 02, 2019 at 06:08:02PM -0700, Andres Freund wrote:
> >>> We're WAY WAY past feature freeze. This isn't the time to rewrite guc.c,
> >>> guc-file.l to be suitable for running outside of a backend environment.
> >
> >> Right. And even if we had the code, it's not quite backpatchable (which
> >> we probably should do, considering this is a general ALTER SYSTEM issue,
> >> so not pg12-only).
> >
> >> Not to mention there's no clear consensus this is actually desirable.
> >> I'd argue forcing external tools (written in arbitrary language) to use
> >> this library (written in C), just to modify a "stupid" text file is a
> >> bit overkill. IMO duplicates don't make the file invalid, we should
> >> handle that correctly/gracefully, so I don't see why external tools
> >> could not simply append to the file. We can deduplicate the file when
> >> starting the server, on ALTER SYSTEM, or some other time.
> >
> > Yup. I'd also point out that even if we had a command-line tool of this
> > sort, there would be scenarios where it's not practical or not convenient
> > to use. We need not go further than "my tool needs to work with existing
> > PG releases" to think of good examples.
> I suspect this hasn't been an issue before, simply because until the removal
> of recovery.conf AFAIK there hasn't been a general use-case where you'd need
> to modify while the server is not running. The use-case which now
> exists (i.e. for writing replication configuration) is one where the tool will
> need to be version-aware anyway (like pg_basebackup is), so I don't see that as
> a particular deal-breaker.
> But...
> > I think we should just accept the facts on the ground, which are that
> > some tools modify by appending to it
> +1. It's just a text file...

So are crontab and /etc/passwd, but there are gizmos that help make it
difficult for people to write complete gobbledygook to those. Does it
make sense to discuss tooling of that type?

David Fetter <david(at)fetter(dot)org>
Phone: +1 415 235 3778

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